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systemd/src/shared/mount-util.c
Mike Yuan 7ce2c1bb5f mountpoint-util: rename fd_is_mount_point() to is_mount_point_at() 
fd_* functions in our codebase usually mean fd-specific operations,
while this one actually takes openat()-style params. Rename it
accordingly hence.
2025-01-22 01:37:31 +01:00

1943 lines
79 KiB
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/* SPDX-License-Identifier: LGPL-2.1-or-later */
#include <errno.h>
#include <stdlib.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/statvfs.h>
#include <unistd.h>
#include <linux/loop.h>
#if WANT_LINUX_FS_H
#include <linux/fs.h>
#endif
#include "alloc-util.h"
#include "chase.h"
#include "dissect-image.h"
#include "exec-util.h"
#include "extract-word.h"
#include "fd-util.h"
#include "fileio.h"
#include "fs-util.h"
#include "fstab-util.h"
#include "glyph-util.h"
#include "hashmap.h"
#include "initrd-util.h"
#include "label-util.h"
#include "libmount-util.h"
#include "missing_mount.h"
#include "missing_syscall.h"
#include "mkdir-label.h"
#include "mount-util.h"
#include "mountpoint-util.h"
#include "namespace-util.h"
#include "parse-util.h"
#include "path-util.h"
#include "process-util.h"
#include "set.h"
#include "sort-util.h"
#include "stat-util.h"
#include "stdio-util.h"
#include "string-table.h"
#include "string-util.h"
#include "strv.h"
#include "tmpfile-util.h"
#include "user-util.h"
int umount_recursive_full(const char *prefix, int flags, char **keep) {
_cleanup_fclose_ FILE *f = NULL;
int n = 0, r;
/* Try to umount everything recursively below a directory. Also, take care of stacked mounts, and
* keep unmounting them until they are gone. */
f = fopen("/proc/self/mountinfo", "re"); /* Pin the file, in case we unmount /proc/ as part of the logic here */
if (!f)
return log_debug_errno(errno, "Failed to open /proc/self/mountinfo: %m");
for (;;) {
_cleanup_(mnt_free_tablep) struct libmnt_table *table = NULL;
_cleanup_(mnt_free_iterp) struct libmnt_iter *iter = NULL;
bool again = false;
r = libmount_parse("/proc/self/mountinfo", f, &table, &iter);
if (r < 0)
return log_debug_errno(r, "Failed to parse /proc/self/mountinfo: %m");
for (;;) {
bool shall_keep = false;
struct libmnt_fs *fs;
const char *path;
r = mnt_table_next_fs(table, iter, &fs);
if (r == 1)
break;
if (r < 0)
return log_debug_errno(r, "Failed to get next entry from /proc/self/mountinfo: %m");
path = mnt_fs_get_target(fs);
if (!path)
continue;
if (prefix && !path_startswith(path, prefix)) {
// FIXME: This is extremely noisy, we're probably doing something very wrong
// to trigger this so often, needs more investigation.
// log_trace("Not unmounting %s, outside of prefix: %s", path, prefix);
continue;
}
STRV_FOREACH(k, keep)
/* Match against anything in the path to the dirs to keep, or below the dirs to keep */
if (path_startswith(path, *k) || path_startswith(*k, path)) {
shall_keep = true;
break;
}
if (shall_keep) {
log_debug("Not unmounting %s, referenced by keep list.", path);
continue;
}
if (umount2(path, flags | UMOUNT_NOFOLLOW) < 0) {
log_debug_errno(errno, "Failed to umount %s, ignoring: %m", path);
continue;
}
log_trace("Successfully unmounted %s", path);
again = true;
n++;
break;
}
if (!again)
break;
rewind(f);
}
return n;
}
#define MS_CONVERTIBLE_FLAGS (MS_RDONLY|MS_NOSUID|MS_NODEV|MS_NOEXEC|MS_NOSYMFOLLOW)
static uint64_t ms_flags_to_mount_attr(unsigned long a) {
uint64_t f = 0;
if (FLAGS_SET(a, MS_RDONLY))
f |= MOUNT_ATTR_RDONLY;
if (FLAGS_SET(a, MS_NOSUID))
f |= MOUNT_ATTR_NOSUID;
if (FLAGS_SET(a, MS_NODEV))
f |= MOUNT_ATTR_NODEV;
if (FLAGS_SET(a, MS_NOEXEC))
f |= MOUNT_ATTR_NOEXEC;
if (FLAGS_SET(a, MS_NOSYMFOLLOW))
f |= MOUNT_ATTR_NOSYMFOLLOW;
return f;
}
static bool skip_mount_set_attr = false;
/* Use this function only if you do not have direct access to /proc/self/mountinfo but the caller can open it
* for you. This is the case when /proc is masked or not mounted. Otherwise, use bind_remount_recursive. */
int bind_remount_recursive_with_mountinfo(
const char *prefix,
unsigned long new_flags,
unsigned long flags_mask,
char **deny_list,
FILE *proc_self_mountinfo) {
_cleanup_fclose_ FILE *proc_self_mountinfo_opened = NULL;
_cleanup_set_free_ Set *done = NULL;
unsigned n_tries = 0;
int r;
assert(prefix);
if ((flags_mask & ~MS_CONVERTIBLE_FLAGS) == 0 && strv_isempty(deny_list) && !skip_mount_set_attr) {
/* Let's take a shortcut for all the flags we know how to convert into mount_setattr() flags */
if (mount_setattr(AT_FDCWD, prefix, AT_SYMLINK_NOFOLLOW|AT_RECURSIVE,
&(struct mount_attr) {
.attr_set = ms_flags_to_mount_attr(new_flags & flags_mask),
.attr_clr = ms_flags_to_mount_attr(~new_flags & flags_mask),
}, MOUNT_ATTR_SIZE_VER0) < 0) {
log_debug_errno(errno, "mount_setattr() failed, falling back to classic remounting: %m");
/* We fall through to classic behaviour if not supported (i.e. kernel < 5.12). We
* also do this for all other kinds of errors since they are so many different, and
* mount_setattr() has no graceful mode where it continues despite seeing errors one
* some mounts, but we want that. Moreover mount_setattr() only works on the mount
* point inode itself, not a non-mount point inode, and we want to support arbitrary
* prefixes here. */
if (ERRNO_IS_NOT_SUPPORTED(errno)) /* if not supported, then don't bother at all anymore */
skip_mount_set_attr = true;
} else
return 0; /* Nice, this worked! */
}
if (!proc_self_mountinfo) {
r = fopen_unlocked("/proc/self/mountinfo", "re", &proc_self_mountinfo_opened);
if (r < 0)
return r;
proc_self_mountinfo = proc_self_mountinfo_opened;
}
/* Recursively remount a directory (and all its submounts) with desired flags (MS_READONLY,
* MS_NOSUID, MS_NOEXEC). If the directory is already mounted, we reuse the mount and simply mark it
* MS_BIND|MS_RDONLY (or remove the MS_RDONLY for read-write operation), ditto for other flags. If it
* isn't we first make it one. Afterwards we apply (or remove) the flags to all submounts we can
* access, too. When mounts are stacked on the same mount point we only care for each individual
* "top-level" mount on each point, as we cannot influence/access the underlying mounts anyway. We do
* not have any effect on future submounts that might get propagated, they might be writable
* etc. This includes future submounts that have been triggered via autofs. Also note that we can't
* operate atomically here. Mounts established while we process the tree might or might not get
* noticed and thus might or might not be covered.
*
* If the "deny_list" parameter is specified it may contain a list of subtrees to exclude from the
* remount operation. Note that we'll ignore the deny list for the top-level path. */
for (;;) {
_cleanup_(mnt_free_tablep) struct libmnt_table *table = NULL;
_cleanup_(mnt_free_iterp) struct libmnt_iter *iter = NULL;
_cleanup_hashmap_free_ Hashmap *todo = NULL;
bool top_autofs = false;
if (n_tries++ >= 32) /* Let's not retry this loop forever */
return -EBUSY;
rewind(proc_self_mountinfo);
r = libmount_parse("/proc/self/mountinfo", proc_self_mountinfo, &table, &iter);
if (r < 0)
return log_debug_errno(r, "Failed to parse /proc/self/mountinfo: %m");
for (;;) {
_cleanup_free_ char *d = NULL;
const char *path, *type, *opts;
unsigned long flags = 0;
struct libmnt_fs *fs;
r = mnt_table_next_fs(table, iter, &fs);
if (r == 1) /* EOF */
break;
if (r < 0)
return log_debug_errno(r, "Failed to get next entry from /proc/self/mountinfo: %m");
path = mnt_fs_get_target(fs);
if (!path)
continue;
if (!path_startswith(path, prefix))
continue;
type = mnt_fs_get_fstype(fs);
if (!type)
continue;
/* Let's ignore autofs mounts. If they aren't triggered yet, we want to avoid
* triggering them, as we don't make any guarantees for future submounts anyway. If
* they are already triggered, then we will find another entry for this. */
if (streq(type, "autofs")) {
top_autofs = top_autofs || path_equal(path, prefix);
continue;
}
if (set_contains(done, path))
continue;
/* Ignore this mount if it is deny-listed, but only if it isn't the top-level mount
* we shall operate on. */
if (!path_equal(path, prefix)) {
bool deny_listed = false;
STRV_FOREACH(i, deny_list) {
if (path_equal(*i, prefix))
continue;
if (!path_startswith(*i, prefix))
continue;
if (path_startswith(path, *i)) {
deny_listed = true;
log_trace("Not remounting %s deny-listed by %s, called for %s", path, *i, prefix);
break;
}
}
if (deny_listed)
continue;
}
opts = mnt_fs_get_vfs_options(fs);
if (opts) {
r = mnt_optstr_get_flags(opts, &flags, mnt_get_builtin_optmap(MNT_LINUX_MAP));
if (r < 0)
log_debug_errno(r, "Could not get flags for '%s', ignoring: %m", path);
}
d = strdup(path);
if (!d)
return -ENOMEM;
r = hashmap_ensure_put(&todo, &path_hash_ops_free, d, ULONG_TO_PTR(flags));
if (r == -EEXIST)
/* If the same path was recorded, but with different mount flags, update it:
* it means a mount point is overmounted, and libmount returns the "bottom" (or
* older one) first, but we want to reapply the flags from the "top" (or newer
* one). See: https://github.com/systemd/systemd/issues/20032
* Note that this shouldn't really fail, as we were just told that the key
* exists, and it's an update so we want 'd' to be freed immediately. */
r = hashmap_update(todo, d, ULONG_TO_PTR(flags));
if (r < 0)
return r;
if (r > 0)
TAKE_PTR(d);
}
/* Check if the top-level directory was among what we have seen so far. For that check both
* 'done' and 'todo'. Also check 'top_autofs' because if the top-level dir is an autofs we'll
* not include it in either set but will set this bool. */
if (!set_contains(done, prefix) &&
!(top_autofs || hashmap_contains(todo, prefix))) {
/* The prefix directory itself is not yet a mount, make it one. */
r = mount_nofollow(prefix, prefix, NULL, MS_BIND|MS_REC, NULL);
if (r < 0)
return r;
/* Immediately rescan, so that we pick up the new mount's flags */
continue;
}
/* If we have no submounts to process anymore, we are done */
if (hashmap_isempty(todo))
return 0;
for (;;) {
unsigned long flags;
char *x = NULL;
/* Take the first mount from our list of mounts to still process */
flags = PTR_TO_ULONG(hashmap_steal_first_key_and_value(todo, (void**) &x));
if (!x)
break;
r = set_ensure_consume(&done, &path_hash_ops_free, x);
if (IN_SET(r, 0, -EEXIST))
continue; /* Already done */
if (r < 0)
return r;
/* Now, remount this with the new flags set, but exclude MS_RELATIME from it. (It's
* the default anyway, thus redundant, and in userns we'll get an error if we try to
* explicitly enable it) */
r = mount_nofollow(NULL, x, NULL, ((flags & ~flags_mask)|MS_BIND|MS_REMOUNT|new_flags) & ~MS_RELATIME, NULL);
if (r < 0) {
int q;
/* OK, so the remount of this entry failed. We'll ultimately ignore this in
* almost all cases (there are simply so many reasons why this can fail,
* think autofs, NFS, FUSE, …), but let's generate useful debug messages at
* the very least. */
q = path_is_mount_point(x);
if (IN_SET(q, 0, -ENOENT)) {
/* Hmm, whaaaa? The mount point is not actually a mount point? Then
* it is either obstructed by a later mount or somebody has been
* racing against us and removed it. Either way the mount point
* doesn't matter to us, let's ignore it hence. */
log_debug_errno(r, "Mount point '%s' to remount is not a mount point anymore, ignoring remount failure: %m", x);
continue;
}
if (q < 0) /* Any other error on this? Just log and continue */
log_debug_errno(q, "Failed to determine whether '%s' is a mount point or not, ignoring: %m", x);
if (((flags ^ new_flags) & flags_mask & ~MS_RELATIME) == 0) { /* ignore MS_RELATIME while comparing */
log_debug_errno(r, "Couldn't remount '%s', but the flags already match what we want, hence ignoring: %m", x);
continue;
}
/* Make this fatal if this is the top-level mount */
if (path_equal(x, prefix))
return r;
/* If this is not the top-level mount, then handle this gracefully: log but
* otherwise ignore. With NFS, FUSE, autofs there are just too many reasons
* this might fail without a chance for us to do anything about it, let's
* hence be strict on the top-level mount and lenient on the inner ones. */
log_debug_errno(r, "Couldn't remount submount '%s' for unexpected reason, ignoring: %m", x);
continue;
}
log_trace("Remounted %s.", x);
}
}
}
int bind_remount_one_with_mountinfo(
const char *path,
unsigned long new_flags,
unsigned long flags_mask,
FILE *proc_self_mountinfo) {
_cleanup_(mnt_free_tablep) struct libmnt_table *table = NULL;
unsigned long flags = 0;
struct libmnt_fs *fs;
const char *opts;
int r;
assert(path);
assert(proc_self_mountinfo);
if ((flags_mask & ~MS_CONVERTIBLE_FLAGS) == 0 && !skip_mount_set_attr) {
/* Let's take a shortcut for all the flags we know how to convert into mount_setattr() flags */
if (mount_setattr(AT_FDCWD, path, AT_SYMLINK_NOFOLLOW,
&(struct mount_attr) {
.attr_set = ms_flags_to_mount_attr(new_flags & flags_mask),
.attr_clr = ms_flags_to_mount_attr(~new_flags & flags_mask),
}, MOUNT_ATTR_SIZE_VER0) < 0) {
log_debug_errno(errno, "mount_setattr() didn't work, falling back to classic remounting: %m");
if (ERRNO_IS_NOT_SUPPORTED(errno)) /* if not supported, then don't bother at all anymore */
skip_mount_set_attr = true;
} else
return 0; /* Nice, this worked! */
}
rewind(proc_self_mountinfo);
table = mnt_new_table();
if (!table)
return -ENOMEM;
r = mnt_table_parse_stream(table, proc_self_mountinfo, "/proc/self/mountinfo");
if (r < 0)
return r;
fs = mnt_table_find_target(table, path, MNT_ITER_FORWARD);
if (!fs) {
r = access_nofollow(path, F_OK); /* Hmm, it's not in the mount table, but does it exist at all? */
if (r < 0)
return r;
return -EINVAL; /* Not a mount point we recognize */
}
opts = mnt_fs_get_vfs_options(fs);
if (opts) {
r = mnt_optstr_get_flags(opts, &flags, mnt_get_builtin_optmap(MNT_LINUX_MAP));
if (r < 0)
log_debug_errno(r, "Could not get flags for '%s', ignoring: %m", path);
}
r = mount_nofollow(NULL, path, NULL, ((flags & ~flags_mask)|MS_BIND|MS_REMOUNT|new_flags) & ~MS_RELATIME, NULL);
if (r < 0) {
if (((flags ^ new_flags) & flags_mask & ~MS_RELATIME) != 0) /* Ignore MS_RELATIME again,
* since kernel adds it in
* everywhere, because it's the
* default. */
return r;
/* Let's handle redundant remounts gracefully */
log_debug_errno(r, "Failed to remount '%s' but flags already match what we want, ignoring: %m", path);
}
return 0;
}
int bind_remount_one(const char *path, unsigned long new_flags, unsigned long flags_mask) {
_cleanup_fclose_ FILE *proc_self_mountinfo = NULL;
proc_self_mountinfo = fopen("/proc/self/mountinfo", "re");
if (!proc_self_mountinfo)
return log_debug_errno(errno, "Failed to open /proc/self/mountinfo: %m");
return bind_remount_one_with_mountinfo(path, new_flags, flags_mask, proc_self_mountinfo);
}
static int mount_switch_root_pivot(int fd_newroot, const char *path) {
assert(fd_newroot >= 0);
assert(path);
/* Let the kernel tuck the new root under the old one. */
if (pivot_root(".", ".") < 0)
return log_debug_errno(errno, "Failed to pivot root to new rootfs '%s': %m", path);
/* Get rid of the old root and reveal our brand new root. (This will always operate on the top-most
* mount on our cwd, regardless what our current directory actually points to.) */
if (umount2(".", MNT_DETACH) < 0)
return log_debug_errno(errno, "Failed to unmount old rootfs: %m");
return 0;
}
static int mount_switch_root_move(int fd_newroot, const char *path) {
assert(fd_newroot >= 0);
assert(path);
/* Move the new root fs */
if (mount(".", "/", NULL, MS_MOVE, NULL) < 0)
return log_debug_errno(errno, "Failed to move new rootfs '%s': %m", path);
/* Also change root dir */
if (chroot(".") < 0)
return log_debug_errno(errno, "Failed to chroot to new rootfs '%s': %m", path);
return 0;
}
int mount_switch_root_full(const char *path, unsigned long mount_propagation_flag, bool force_ms_move) {
_cleanup_close_ int fd_newroot = -EBADF;
int r, is_current_root;
assert(path);
assert(mount_propagation_flag_is_valid(mount_propagation_flag));
fd_newroot = open(path, O_PATH|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW);
if (fd_newroot < 0)
return log_debug_errno(errno, "Failed to open new rootfs '%s': %m", path);
is_current_root = path_is_root_at(fd_newroot, NULL);
if (is_current_root < 0)
return log_debug_errno(is_current_root, "Failed to determine if target dir is our root already: %m");
/* Change into the new rootfs. */
if (fchdir(fd_newroot) < 0)
return log_debug_errno(errno, "Failed to chdir into new rootfs '%s': %m", path);
/* Make this a NOP if we are supposed to switch to our current root fs. After all, both pivot_root()
* and MS_MOVE don't like that. */
if (!is_current_root) {
if (!force_ms_move) {
r = mount_switch_root_pivot(fd_newroot, path);
if (r < 0) {
log_debug_errno(r, "Failed to pivot into new rootfs '%s', will try to use MS_MOVE instead: %m", path);
force_ms_move = true;
}
}
if (force_ms_move) {
/* Failed to pivot_root() fallback to MS_MOVE. For example, this may happen if the rootfs is
* an initramfs in which case pivot_root() isn't supported. */
r = mount_switch_root_move(fd_newroot, path);
if (r < 0)
return log_debug_errno(r, "Failed to switch to new rootfs '%s' with MS_MOVE: %m", path);
}
}
log_debug("Successfully switched root to '%s'.", path);
/* Finally, let's establish the requested propagation flags. */
if (mount_propagation_flag == 0)
return 0;
if (mount(NULL, ".", NULL, mount_propagation_flag | MS_REC, NULL) < 0)
return log_debug_errno(errno, "Failed to turn new rootfs '%s' into %s mount: %m",
mount_propagation_flag_to_string(mount_propagation_flag), path);
return 0;
}
int repeat_unmount(const char *path, int flags) {
bool done = false;
assert(path);
/* If there are multiple mounts on a mount point, this
* removes them all */
for (;;) {
if (umount2(path, flags) < 0) {
if (errno == EINVAL)
return done;
return -errno;
}
done = true;
}
}
int mode_to_inaccessible_node(
const char *runtime_dir,
mode_t mode,
char **ret) {
/* This function maps a node type to a corresponding inaccessible file node. These nodes are created
* during early boot by PID 1. In some cases we lacked the privs to create the character and block
* devices (maybe because we run in an userns environment, or miss CAP_SYS_MKNOD, or run with a
* devices policy that excludes device nodes with major and minor of 0), but that's fine, in that
* case we use an AF_UNIX file node instead, which is not the same, but close enough for most
* uses. And most importantly, the kernel allows bind mounts from socket nodes to any non-directory
* file nodes, and that's the most important thing that matters.
*
* Note that the runtime directory argument shall be the top-level runtime directory, i.e. /run/ if
* we operate in system context and $XDG_RUNTIME_DIR if we operate in user context. */
_cleanup_free_ char *d = NULL;
const char *node;
assert(ret);
if (!runtime_dir)
runtime_dir = "/run";
if (S_ISLNK(mode))
return -EINVAL;
node = inode_type_to_string(mode);
if (!node)
return -EINVAL;
d = path_join(runtime_dir, "systemd/inaccessible", node);
if (!d)
return -ENOMEM;
/* On new kernels unprivileged users are permitted to create 0:0 char device nodes (because they also
* act as whiteout inode for overlayfs), but no other char or block device nodes. On old kernels no
* device node whatsoever may be created by unprivileged processes. Hence, if the caller asks for the
* inaccessible block device node let's see if the block device node actually exists, and if not,
* fall back to the character device node. From there fall back to the socket device node. This means
* in the best case we'll get the right device node type — but if not we'll hopefully at least get a
* device node at all. */
if (S_ISBLK(mode) &&
access(d, F_OK) < 0 && errno == ENOENT) {
free(d);
d = path_join(runtime_dir, "/systemd/inaccessible/chr");
if (!d)
return -ENOMEM;
}
if (IN_SET(mode & S_IFMT, S_IFBLK, S_IFCHR) &&
access(d, F_OK) < 0 && errno == ENOENT) {
free(d);
d = path_join(runtime_dir, "/systemd/inaccessible/sock");
if (!d)
return -ENOMEM;
}
*ret = TAKE_PTR(d);
return 0;
}
int mount_flags_to_string(unsigned long flags, char **ret) {
static const struct {
unsigned long flag;
const char *name;
} map[] = {
{ .flag = MS_RDONLY, .name = "MS_RDONLY", },
{ .flag = MS_NOSUID, .name = "MS_NOSUID", },
{ .flag = MS_NODEV, .name = "MS_NODEV", },
{ .flag = MS_NOEXEC, .name = "MS_NOEXEC", },
{ .flag = MS_SYNCHRONOUS, .name = "MS_SYNCHRONOUS", },
{ .flag = MS_REMOUNT, .name = "MS_REMOUNT", },
{ .flag = MS_MANDLOCK, .name = "MS_MANDLOCK", },
{ .flag = MS_DIRSYNC, .name = "MS_DIRSYNC", },
{ .flag = MS_NOSYMFOLLOW, .name = "MS_NOSYMFOLLOW", },
{ .flag = MS_NOATIME, .name = "MS_NOATIME", },
{ .flag = MS_NODIRATIME, .name = "MS_NODIRATIME", },
{ .flag = MS_BIND, .name = "MS_BIND", },
{ .flag = MS_MOVE, .name = "MS_MOVE", },
{ .flag = MS_REC, .name = "MS_REC", },
{ .flag = MS_SILENT, .name = "MS_SILENT", },
{ .flag = MS_POSIXACL, .name = "MS_POSIXACL", },
{ .flag = MS_UNBINDABLE, .name = "MS_UNBINDABLE", },
{ .flag = MS_PRIVATE, .name = "MS_PRIVATE", },
{ .flag = MS_SLAVE, .name = "MS_SLAVE", },
{ .flag = MS_SHARED, .name = "MS_SHARED", },
{ .flag = MS_RELATIME, .name = "MS_RELATIME", },
{ .flag = MS_KERNMOUNT, .name = "MS_KERNMOUNT", },
{ .flag = MS_I_VERSION, .name = "MS_I_VERSION", },
{ .flag = MS_STRICTATIME, .name = "MS_STRICTATIME", },
{ .flag = MS_LAZYTIME, .name = "MS_LAZYTIME", },
};
_cleanup_free_ char *str = NULL;
assert(ret);
FOREACH_ELEMENT(entry, map)
if (flags & entry->flag) {
if (!strextend_with_separator(&str, "|", entry->name))
return -ENOMEM;
flags &= ~entry->flag;
}
if (!str || flags != 0)
if (strextendf_with_separator(&str, "|", "%lx", flags) < 0)
return -ENOMEM;
*ret = TAKE_PTR(str);
return 0;
}
int mount_verbose_full(
int error_log_level,
const char *what,
const char *where,
const char *type,
unsigned long flags,
const char *options,
bool follow_symlink) {
_cleanup_free_ char *fl = NULL, *o = NULL;
unsigned long f;
int r;
r = mount_option_mangle(options, flags, &f, &o);
if (r < 0)
return log_full_errno(error_log_level, r,
"Failed to mangle mount options %s: %m",
strempty(options));
(void) mount_flags_to_string(f, &fl);
if (FLAGS_SET(f, MS_REMOUNT|MS_BIND))
log_debug("Changing mount flags %s (%s \"%s\")...",
where, strnull(fl), strempty(o));
else if (f & MS_REMOUNT)
log_debug("Remounting superblock %s (%s \"%s\")...",
where, strnull(fl), strempty(o));
else if (f & (MS_SHARED|MS_PRIVATE|MS_SLAVE|MS_UNBINDABLE))
log_debug("Changing mount propagation %s (%s \"%s\")",
where, strnull(fl), strempty(o));
else if (f & MS_BIND)
log_debug("Bind-mounting %s on %s (%s \"%s\")...",
what, where, strnull(fl), strempty(o));
else if (f & MS_MOVE)
log_debug("Moving mount %s %s %s (%s \"%s\")...",
what, special_glyph(SPECIAL_GLYPH_ARROW_RIGHT), where, strnull(fl), strempty(o));
else
log_debug("Mounting %s (%s) on %s (%s \"%s\")...",
strna(what), strna(type), where, strnull(fl), strempty(o));
if (follow_symlink)
r = RET_NERRNO(mount(what, where, type, f, o));
else
r = mount_nofollow(what, where, type, f, o);
if (r < 0)
return log_full_errno(error_log_level, r,
"Failed to mount %s (type %s) on %s (%s \"%s\"): %m",
strna(what), strna(type), where, strnull(fl), strempty(o));
return 0;
}
int umount_verbose(
int error_log_level,
const char *where,
int flags) {
assert(where);
log_debug("Unmounting '%s'...", where);
if (umount2(where, flags) < 0)
return log_full_errno(error_log_level, errno, "Failed to unmount '%s': %m", where);
return 0;
}
int umountat_detach_verbose(
int error_log_level,
int fd,
const char *where) {
/* Similar to umountat_verbose(), but goes by fd + path. This implies MNT_DETACH, since to do this we
* must pin the inode in question via an fd. */
assert(fd >= 0 || fd == AT_FDCWD);
/* If neither fd nor path are specified take this as reference to the cwd */
if (fd == AT_FDCWD && isempty(where))
return umount_verbose(error_log_level, ".", MNT_DETACH|UMOUNT_NOFOLLOW);
/* If we don't actually take the fd into consideration for this operation shortcut things, so that we
* don't have to open the inode */
if (fd == AT_FDCWD || path_is_absolute(where))
return umount_verbose(error_log_level, where, MNT_DETACH|UMOUNT_NOFOLLOW);
_cleanup_free_ char *prefix = NULL;
const char *p;
if (fd_get_path(fd, &prefix) < 0)
p = "<fd>"; /* if we can't get the path, return something vaguely useful */
else
p = prefix;
_cleanup_free_ char *joined = isempty(where) ? strdup(p) : path_join(p, where);
log_debug("Unmounting '%s'...", strna(joined));
_cleanup_close_ int inode_fd = -EBADF;
int mnt_fd;
if (isempty(where))
mnt_fd = fd;
else {
inode_fd = openat(fd, where, O_PATH|O_CLOEXEC|O_NOFOLLOW);
if (inode_fd < 0)
return log_full_errno(error_log_level, errno, "Failed to pin '%s': %m", strna(joined));
mnt_fd = inode_fd;
}
if (umount2(FORMAT_PROC_FD_PATH(mnt_fd), MNT_DETACH) < 0)
return log_full_errno(error_log_level, errno, "Failed to unmount '%s': %m", strna(joined));
return 0;
}
int mount_exchange_graceful(int fsmount_fd, const char *dest, bool mount_beneath) {
int r;
assert(fsmount_fd >= 0);
assert(dest);
/* First, try to mount beneath an existing mount point, and if that works, umount the old mount,
* which is now at the top. This will ensure we can atomically replace a mount. Note that this works
* also in the case where there are submounts down the tree. Mount propagation is allowed but
* restricted to layouts that don't end up propagation the new mount on top of the mount stack. If
* this is not supported (minimum kernel v6.5), or if there is no mount on the mountpoint, we get
* -EINVAL and then we fallback to normal mounting. */
r = RET_NERRNO(move_mount(fsmount_fd, /* from_path = */ "",
/* to_fd = */ -EBADF, dest,
MOVE_MOUNT_F_EMPTY_PATH | (mount_beneath ? MOVE_MOUNT_BENEATH : 0)));
if (mount_beneath) {
if (r >= 0) /* Mounting beneath worked! Now unmount the upper mount. */
return umount_verbose(LOG_DEBUG, dest, UMOUNT_NOFOLLOW|MNT_DETACH);
if (r == -EINVAL) { /* Fallback if mount_beneath is not supported */
log_debug_errno(r,
"Cannot mount beneath '%s', falling back to overmount: %m",
dest);
return mount_exchange_graceful(fsmount_fd, dest, /* mount_beneath = */ false);
}
}
return r;
}
int mount_option_mangle(
const char *options,
unsigned long mount_flags,
unsigned long *ret_mount_flags,
char **ret_remaining_options) {
const struct libmnt_optmap *map;
_cleanup_free_ char *ret = NULL;
int r;
/* This extracts mount flags from the mount options, and stores
* non-mount-flag options to '*ret_remaining_options'.
* E.g.,
* "rw,nosuid,nodev,relatime,size=1630748k,mode=0700,uid=1000,gid=1000"
* is split to MS_NOSUID|MS_NODEV|MS_RELATIME and
* "size=1630748k,mode=0700,uid=1000,gid=1000".
* See more examples in test-mount-util.c.
*
* If 'options' does not contain any non-mount-flag options,
* then '*ret_remaining_options' is set to NULL instead of empty string.
* The validity of options stored in '*ret_remaining_options' is not checked.
* If 'options' is NULL, this just copies 'mount_flags' to *ret_mount_flags. */
assert(ret_mount_flags);
assert(ret_remaining_options);
map = mnt_get_builtin_optmap(MNT_LINUX_MAP);
if (!map)
return -EINVAL;
for (const char *p = options;;) {
_cleanup_free_ char *word = NULL;
const struct libmnt_optmap *ent;
r = extract_first_word(&p, &word, ",", EXTRACT_KEEP_QUOTE);
if (r < 0)
return r;
if (r == 0)
break;
for (ent = map; ent->name; ent++) {
/* All entries in MNT_LINUX_MAP do not take any argument.
* Thus, ent->name does not contain "=" or "[=]". */
if (!streq(word, ent->name))
continue;
if (!(ent->mask & MNT_INVERT))
mount_flags |= ent->id;
else
mount_flags &= ~ent->id;
break;
}
/* If 'word' is not a mount flag, then store it in '*ret_remaining_options'. */
if (!ent->name &&
!startswith_no_case(word, "x-") &&
!strextend_with_separator(&ret, ",", word))
return -ENOMEM;
}
*ret_mount_flags = mount_flags;
*ret_remaining_options = TAKE_PTR(ret);
return 0;
}
static int mount_in_namespace_legacy(
const char *chased_src_path,
int chased_src_fd,
struct stat *chased_src_st,
const char *propagate_path,
const char *incoming_path,
const char *dest,
int pidns_fd,
int mntns_fd,
int root_fd,
MountInNamespaceFlags flags,
const MountOptions *options,
const ImagePolicy *image_policy) {
_cleanup_close_pair_ int errno_pipe_fd[2] = EBADF_PAIR;
char mount_slave[] = "/tmp/propagate.XXXXXX", *mount_tmp, *mount_outside, *p;
bool mount_slave_created = false, mount_slave_mounted = false,
mount_tmp_created = false, mount_tmp_mounted = false,
mount_outside_created = false, mount_outside_mounted = false;
pid_t child;
int r;
assert(chased_src_path);
assert(chased_src_fd >= 0);
assert(chased_src_st);
assert(propagate_path);
assert(incoming_path);
assert(dest);
assert(pidns_fd >= 0);
assert(mntns_fd >= 0);
assert(root_fd >= 0);
assert(!options || (flags & MOUNT_IN_NAMESPACE_IS_IMAGE));
p = strjoina(propagate_path, "/");
r = access_nofollow(p, F_OK);
if (r < 0)
return log_debug_errno(r == -ENOENT ? SYNTHETIC_ERRNO(EOPNOTSUPP) : r, "Target does not allow propagation of mount points");
/* Our goal is to install a new bind mount into the container,
possibly read-only. This is irritatingly complex
unfortunately, currently.
First, we start by creating a private playground in /tmp,
that we can mount MS_SLAVE. (Which is necessary, since
MS_MOVE cannot be applied to mounts with MS_SHARED parent
mounts.) */
if (!mkdtemp(mount_slave))
return log_debug_errno(errno, "Failed to create playground %s: %m", mount_slave);
mount_slave_created = true;
r = mount_nofollow_verbose(LOG_DEBUG, mount_slave, mount_slave, NULL, MS_BIND, NULL);
if (r < 0)
goto finish;
mount_slave_mounted = true;
r = mount_nofollow_verbose(LOG_DEBUG, NULL, mount_slave, NULL, MS_SLAVE, NULL);
if (r < 0)
goto finish;
/* Second, we mount the source file or directory to a directory inside of our MS_SLAVE playground. */
mount_tmp = strjoina(mount_slave, "/mount");
if (flags & MOUNT_IN_NAMESPACE_IS_IMAGE)
r = mkdir_p(mount_tmp, 0700);
else
r = make_mount_point_inode_from_stat(chased_src_st, mount_tmp, 0700);
if (r < 0) {
log_debug_errno(r, "Failed to create temporary mount point %s: %m", mount_tmp);
goto finish;
}
mount_tmp_created = true;
if (flags & MOUNT_IN_NAMESPACE_IS_IMAGE)
r = verity_dissect_and_mount(
chased_src_fd,
chased_src_path,
mount_tmp,
options,
image_policy,
/* required_host_os_release_id= */ NULL,
/* required_host_os_release_version_id= */ NULL,
/* required_host_os_release_sysext_level= */ NULL,
/* required_host_os_release_confext_level= */ NULL,
/* required_sysext_scope= */ NULL,
/* verity= */ NULL,
/* ret_image= */ NULL);
else
r = mount_follow_verbose(LOG_DEBUG, FORMAT_PROC_FD_PATH(chased_src_fd), mount_tmp, NULL, MS_BIND, NULL);
if (r < 0)
goto finish;
mount_tmp_mounted = true;
/* Third, we remount the new bind mount read-only if requested. */
if (flags & MOUNT_IN_NAMESPACE_READ_ONLY) {
r = mount_nofollow_verbose(LOG_DEBUG, NULL, mount_tmp, NULL, MS_BIND|MS_REMOUNT|MS_RDONLY, NULL);
if (r < 0)
goto finish;
}
/* Fourth, we move the new bind mount into the propagation directory. This way it will appear there read-only
* right-away. */
mount_outside = strjoina(propagate_path, "/XXXXXX");
if ((flags & MOUNT_IN_NAMESPACE_IS_IMAGE) || S_ISDIR(chased_src_st->st_mode))
r = mkdtemp(mount_outside) ? 0 : -errno;
else {
r = mkostemp_safe(mount_outside);
safe_close(r);
}
if (r < 0) {
log_debug_errno(r, "Cannot create propagation file or directory %s: %m", mount_outside);
goto finish;
}
mount_outside_created = true;
r = mount_nofollow_verbose(LOG_DEBUG, mount_tmp, mount_outside, NULL, MS_MOVE, NULL);
if (r < 0)
goto finish;
mount_outside_mounted = true;
mount_tmp_mounted = false;
if ((flags & MOUNT_IN_NAMESPACE_IS_IMAGE) || S_ISDIR(chased_src_st->st_mode))
(void) rmdir(mount_tmp);
else
(void) unlink(mount_tmp);
mount_tmp_created = false;
(void) umount_verbose(LOG_DEBUG, mount_slave, UMOUNT_NOFOLLOW);
mount_slave_mounted = false;
(void) rmdir(mount_slave);
mount_slave_created = false;
if (pipe2(errno_pipe_fd, O_CLOEXEC|O_NONBLOCK) < 0) {
log_debug_errno(errno, "Failed to create pipe: %m");
goto finish;
}
r = namespace_fork("(sd-bindmnt)", "(sd-bindmnt-inner)", NULL, 0, FORK_RESET_SIGNALS|FORK_DEATHSIG_SIGTERM,
pidns_fd, mntns_fd, -1, -1, root_fd, &child);
if (r < 0)
goto finish;
if (r == 0) {
_cleanup_free_ char *mount_outside_fn = NULL, *mount_inside = NULL;
errno_pipe_fd[0] = safe_close(errno_pipe_fd[0]);
if (flags & MOUNT_IN_NAMESPACE_MAKE_FILE_OR_DIRECTORY) {
if (!(flags & MOUNT_IN_NAMESPACE_IS_IMAGE)) {
(void) mkdir_parents(dest, 0755);
(void) make_mount_point_inode_from_stat(chased_src_st, dest, 0700);
} else
(void) mkdir_p(dest, 0755);
}
/* Fifth, move the mount to the right place inside */
r = path_extract_filename(mount_outside, &mount_outside_fn);
if (r < 0) {
log_debug_errno(r, "Failed to extract filename from propagation file or directory '%s': %m", mount_outside);
report_errno_and_exit(errno_pipe_fd[1], r);
}
mount_inside = path_join(incoming_path, mount_outside_fn);
if (!mount_inside)
report_errno_and_exit(errno_pipe_fd[1], log_oom_debug());
r = mount_nofollow_verbose(LOG_DEBUG, mount_inside, dest, NULL, MS_MOVE, NULL);
if (r < 0)
report_errno_and_exit(errno_pipe_fd[1], r);
_exit(EXIT_SUCCESS);
}
errno_pipe_fd[1] = safe_close(errno_pipe_fd[1]);
r = wait_for_terminate_and_check("(sd-bindmnt)", child, 0);
if (r < 0) {
log_debug_errno(r, "Failed to wait for child: %m");
goto finish;
}
if (r != EXIT_SUCCESS) {
if (read(errno_pipe_fd[0], &r, sizeof(r)) == sizeof(r))
log_debug_errno(r, "Failed to mount: %m");
else
log_debug("Child failed.");
goto finish;
}
finish:
if (mount_outside_mounted)
(void) umount_verbose(LOG_DEBUG, mount_outside, UMOUNT_NOFOLLOW);
if (mount_outside_created) {
if ((flags & MOUNT_IN_NAMESPACE_IS_IMAGE) || S_ISDIR(chased_src_st->st_mode))
(void) rmdir(mount_outside);
else
(void) unlink(mount_outside);
}
if (mount_tmp_mounted)
(void) umount_verbose(LOG_DEBUG, mount_tmp, UMOUNT_NOFOLLOW);
if (mount_tmp_created) {
if ((flags & MOUNT_IN_NAMESPACE_IS_IMAGE) || S_ISDIR(chased_src_st->st_mode))
(void) rmdir(mount_tmp);
else
(void) unlink(mount_tmp);
}
if (mount_slave_mounted)
(void) umount_verbose(LOG_DEBUG, mount_slave, UMOUNT_NOFOLLOW);
if (mount_slave_created)
(void) rmdir(mount_slave);
return r;
}
static int mount_in_namespace(
const PidRef *target,
const char *propagate_path,
const char *incoming_path,
const char *src,
const char *dest,
MountInNamespaceFlags flags,
const MountOptions *options,
const ImagePolicy *image_policy) {
_cleanup_close_ int mntns_fd = -EBADF, root_fd = -EBADF, pidns_fd = -EBADF, chased_src_fd = -EBADF;
_cleanup_free_ char *chased_src_path = NULL;
struct stat st;
int r;
assert(propagate_path);
assert(incoming_path);
assert(src);
assert(dest);
assert((flags & MOUNT_IN_NAMESPACE_IS_IMAGE) || (!options && !image_policy));
if (!pidref_is_set(target))
return -ESRCH;
r = pidref_namespace_open(target, &pidns_fd, &mntns_fd, /* ret_netns_fd = */ NULL, /* ret_userns_fd = */ NULL, &root_fd);
if (r < 0)
return log_debug_errno(r, "Failed to retrieve FDs of the target process' namespace: %m");
r = is_our_namespace(mntns_fd, NAMESPACE_MOUNT);
if (r < 0)
return log_debug_errno(r, "Failed to determine if mount namespaces are equal: %m");
/* We can't add new mounts at runtime if the process wasn't started in a namespace */
if (r > 0)
return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to activate bind mount in target, not running in a mount namespace.");
r = chase(src, NULL, 0, &chased_src_path, &chased_src_fd);
if (r < 0)
return log_debug_errno(r, "Failed to resolve source path '%s': %m", src);
log_debug("Chased source path '%s': %s", src, chased_src_path);
if (fstat(chased_src_fd, &st) < 0)
return log_debug_errno(errno, "Failed to stat() resolved source path '%s': %m", src);
if (S_ISLNK(st.st_mode)) /* This shouldn't really happen, given that we just chased the symlinks above, but let's better be safe… */
return log_debug_errno(SYNTHETIC_ERRNO(ELOOP), "Source path '%s' can't be a symbolic link.", src);
if (!mount_new_api_supported()) /* Fallback if we can't use the new mount API */
return mount_in_namespace_legacy(
chased_src_path,
chased_src_fd,
&st,
propagate_path,
incoming_path,
dest,
pidns_fd,
mntns_fd,
root_fd,
flags,
options,
image_policy);
_cleanup_(dissected_image_unrefp) DissectedImage *img = NULL;
_cleanup_close_ int new_mount_fd = -EBADF;
_cleanup_close_pair_ int errno_pipe_fd[2] = EBADF_PAIR;
pid_t child;
if (flags & MOUNT_IN_NAMESPACE_IS_IMAGE) {
r = verity_dissect_and_mount(
chased_src_fd,
chased_src_path,
/* dest= */ NULL,
options,
image_policy,
/* required_host_os_release_id= */ NULL,
/* required_host_os_release_version_id= */ NULL,
/* required_host_os_release_sysext_level= */ NULL,
/* required_host_os_release_confext_level= */ NULL,
/* required_sysext_scope= */ NULL,
/* verity= */ NULL,
&img);
if (r < 0)
return log_debug_errno(r,
"Failed to dissect and mount image '%s': %m",
chased_src_path);
} else {
new_mount_fd = open_tree(
chased_src_fd,
"",
OPEN_TREE_CLONE|OPEN_TREE_CLOEXEC|AT_SYMLINK_NOFOLLOW|AT_EMPTY_PATH);
if (new_mount_fd < 0)
return log_debug_errno(
errno,
"Failed to open mount source '%s': %m",
chased_src_path);
if ((flags & MOUNT_IN_NAMESPACE_READ_ONLY) && mount_setattr(new_mount_fd, "", AT_EMPTY_PATH,
&(struct mount_attr) {
.attr_set = MOUNT_ATTR_RDONLY,
}, MOUNT_ATTR_SIZE_VER0) < 0)
return log_debug_errno(errno,
"Failed to set mount for '%s' to read only: %m",
chased_src_path);
}
if (pipe2(errno_pipe_fd, O_CLOEXEC|O_NONBLOCK) < 0)
return log_debug_errno(errno, "Failed to create pipe: %m");
r = namespace_fork("(sd-bindmnt)",
"(sd-bindmnt-inner)",
/* except_fds= */ NULL,
/* n_except_fds= */ 0,
FORK_RESET_SIGNALS|FORK_DEATHSIG_SIGTERM,
pidns_fd,
mntns_fd,
/* netns_fd= */ -EBADF,
/* userns_fd= */ -EBADF,
root_fd,
&child);
if (r < 0)
return log_debug_errno(r, "Failed to fork off mount helper into namespace: %m");
if (r == 0) {
errno_pipe_fd[0] = safe_close(errno_pipe_fd[0]);
if (flags & MOUNT_IN_NAMESPACE_MAKE_FILE_OR_DIRECTORY)
(void) mkdir_parents(dest, 0755);
if (img) {
DissectImageFlags f =
DISSECT_IMAGE_TRY_ATOMIC_MOUNT_EXCHANGE |
DISSECT_IMAGE_ALLOW_USERSPACE_VERITY;
if (flags & MOUNT_IN_NAMESPACE_MAKE_FILE_OR_DIRECTORY)
f |= DISSECT_IMAGE_MKDIR;
if (flags & MOUNT_IN_NAMESPACE_READ_ONLY)
f |= DISSECT_IMAGE_READ_ONLY;
r = dissected_image_mount(
img,
dest,
/* uid_shift= */ UID_INVALID,
/* uid_range= */ UID_INVALID,
/* userns_fd= */ -EBADF,
f);
} else {
if (flags & MOUNT_IN_NAMESPACE_MAKE_FILE_OR_DIRECTORY)
(void) make_mount_point_inode_from_stat(&st, dest, 0700);
r = mount_exchange_graceful(new_mount_fd, dest, /* mount_beneath= */ true);
}
report_errno_and_exit(errno_pipe_fd[1], r);
}
errno_pipe_fd[1] = safe_close(errno_pipe_fd[1]);
r = wait_for_terminate_and_check("(sd-bindmnt)", child, 0);
if (r < 0)
return log_debug_errno(r, "Failed to wait for child: %m");
if (r != EXIT_SUCCESS) {
if (read(errno_pipe_fd[0], &r, sizeof(r)) == sizeof(r))
return log_debug_errno(r, "Failed to mount into namespace: %m");
return log_debug_errno(SYNTHETIC_ERRNO(EPROTO), "Child failed.");
}
return 0;
}
int bind_mount_in_namespace(
const PidRef *target,
const char *propagate_path,
const char *incoming_path,
const char *src,
const char *dest,
MountInNamespaceFlags flags) {
return mount_in_namespace(target,
propagate_path,
incoming_path,
src,
dest,
flags & ~MOUNT_IN_NAMESPACE_IS_IMAGE,
/* options = */ NULL,
/* image_policy = */ NULL);
}
int mount_image_in_namespace(
const PidRef *target,
const char *propagate_path,
const char *incoming_path,
const char *src,
const char *dest,
MountInNamespaceFlags flags,
const MountOptions *options,
const ImagePolicy *image_policy) {
return mount_in_namespace(target,
propagate_path,
incoming_path,
src,
dest,
flags | MOUNT_IN_NAMESPACE_IS_IMAGE,
options,
image_policy);
}
int make_mount_point(const char *path) {
int r;
assert(path);
/* If 'path' is already a mount point, does nothing and returns 0. If it is not it makes it one, and returns 1. */
r = path_is_mount_point(path);
if (r < 0)
return log_debug_errno(r, "Failed to determine whether '%s' is a mount point: %m", path);
if (r > 0)
return 0;
r = mount_nofollow_verbose(LOG_DEBUG, path, path, NULL, MS_BIND|MS_REC, NULL);
if (r < 0)
return r;
return 1;
}
int fd_make_mount_point(int fd) {
int r;
assert(fd >= 0);
r = is_mount_point_at(fd, NULL, 0);
if (r < 0)
return log_debug_errno(r, "Failed to determine whether file descriptor is a mount point: %m");
if (r > 0)
return 0;
r = mount_follow_verbose(LOG_DEBUG, FORMAT_PROC_FD_PATH(fd), FORMAT_PROC_FD_PATH(fd), NULL, MS_BIND|MS_REC, NULL);
if (r < 0)
return r;
return 1;
}
int make_userns(uid_t uid_shift, uid_t uid_range, uid_t source_owner, uid_t dest_owner, RemountIdmapping idmapping) {
_cleanup_close_ int userns_fd = -EBADF;
_cleanup_free_ char *line = NULL;
/* Allocates a userns file descriptor with the mapping we need. For this we'll fork off a child
* process whose only purpose is to give us a new user namespace. It's killed when we got it. */
if (!userns_shift_range_valid(uid_shift, uid_range))
return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), "Invalid UID range for user namespace.");
if (IN_SET(idmapping, REMOUNT_IDMAPPING_NONE, REMOUNT_IDMAPPING_HOST_ROOT)) {
if (asprintf(&line, UID_FMT " " UID_FMT " " UID_FMT "\n", 0u, uid_shift, uid_range) < 0)
return log_oom_debug();
/* If requested we'll include an entry in the mapping so that the host root user can make
* changes to the uidmapped mount like it normally would. Specifically, we'll map the user
* with UID_MAPPED_ROOT on the backing fs to UID 0. This is useful, since nspawn code wants
* to create various missing inodes in the OS tree before booting into it, and this becomes
* very easy and straightforward to do if it can just do it under its own regular UID. Note
* that in that case the container's runtime uidmap (i.e. the one the container payload
* processes run in) will leave this UID unmapped, i.e. if we accidentally leave files owned
* by host root in the already uidmapped tree around they'll show up as owned by 'nobody',
* which is safe. (Of course, we shouldn't leave such inodes around, but always chown() them
* to the container's own UID range, but it's good to have a safety net, in case we
* forget it.) */
if (idmapping == REMOUNT_IDMAPPING_HOST_ROOT)
if (strextendf(&line,
UID_FMT " " UID_FMT " " UID_FMT "\n",
UID_MAPPED_ROOT, 0u, 1u) < 0)
return log_oom_debug();
}
if (idmapping == REMOUNT_IDMAPPING_HOST_OWNER) {
/* Remap the owner of the bind mounted directory to the root user within the container. This
* way every file written by root within the container to the bind-mounted directory will
* be owned by the original user from the host. All other users will remain unmapped. */
if (asprintf(&line, UID_FMT " " UID_FMT " " UID_FMT "\n", source_owner, uid_shift, 1u) < 0)
return log_oom_debug();
}
if (idmapping == REMOUNT_IDMAPPING_HOST_OWNER_TO_TARGET_OWNER) {
/* Remap the owner of the bind mounted directory to the owner of the target directory
* within the container. This way every file written by target directory owner within the
* container to the bind-mounted directory will be owned by the original host user.
* All other users will remain unmapped. */
if (asprintf(
&line,
UID_FMT " " UID_FMT " " UID_FMT "\n",
source_owner, dest_owner, 1u) < 0)
return log_oom_debug();
}
/* We always assign the same UID and GID ranges */
userns_fd = userns_acquire(line, line);
if (userns_fd < 0)
return log_debug_errno(userns_fd, "Failed to acquire new userns: %m");
return TAKE_FD(userns_fd);
}
int remount_idmap_fd(
char **paths,
int userns_fd,
uint64_t extra_mount_attr_set) {
int r;
assert(userns_fd >= 0);
/* This remounts all specified paths with the specified userns as idmap. It will do so in the
* order specified in the strv: the expectation is that the top-level directories are at the
* beginning, and nested directories in the right, so that the tree can be built correctly from left
* to right. */
size_t n = strv_length(paths);
if (n == 0) /* Nothing to do? */
return 0;
int *mount_fds = NULL;
size_t n_mounts_fds = 0;
mount_fds = new(int, n);
if (!mount_fds)
return log_oom_debug();
CLEANUP_ARRAY(mount_fds, n_mounts_fds, close_many_and_free);
for (size_t i = 0; i < n; i++) {
int mntfd;
/* Clone the mount point */
mntfd = mount_fds[n_mounts_fds] = open_tree(-EBADF, paths[i], OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC);
if (mount_fds[n_mounts_fds] < 0)
return log_debug_errno(errno, "Failed to open tree of mounted filesystem '%s': %m", paths[i]);
n_mounts_fds++;
/* Set the user namespace mapping attribute on the cloned mount point */
if (mount_setattr(mntfd, "", AT_EMPTY_PATH,
&(struct mount_attr) {
.attr_set = MOUNT_ATTR_IDMAP | extra_mount_attr_set,
.userns_fd = userns_fd,
}, sizeof(struct mount_attr)) < 0)
return log_debug_errno(errno, "Failed to change bind mount attributes for clone of '%s': %m", paths[i]);
}
for (size_t i = n; i > 0; i--) { /* Unmount the paths right-to-left */
/* Remove the old mount points now that we have a idmapped mounts as replacement for all of them */
r = umount_verbose(LOG_DEBUG, paths[i-1], UMOUNT_NOFOLLOW);
if (r < 0)
return r;
}
for (size_t i = 0; i < n; i++) { /* Mount the replacement mounts left-to-right */
/* And place the cloned version in its place */
log_debug("Mounting idmapped fs to '%s'", paths[i]);
if (move_mount(mount_fds[i], "", -EBADF, paths[i], MOVE_MOUNT_F_EMPTY_PATH) < 0)
return log_debug_errno(errno, "Failed to attach UID mapped mount to '%s': %m", paths[i]);
}
return 0;
}
int remount_idmap(
char **p,
uid_t uid_shift,
uid_t uid_range,
uid_t source_owner,
uid_t dest_owner,
RemountIdmapping idmapping) {
_cleanup_close_ int userns_fd = -EBADF;
userns_fd = make_userns(uid_shift, uid_range, source_owner, dest_owner, idmapping);
if (userns_fd < 0)
return userns_fd;
return remount_idmap_fd(p, userns_fd, /* extra_mount_attr_set= */ 0);
}
static void sub_mount_clear(SubMount *s) {
assert(s);
s->path = mfree(s->path);
s->mount_fd = safe_close(s->mount_fd);
}
void sub_mount_array_free(SubMount *s, size_t n) {
assert(s || n == 0);
for (size_t i = 0; i < n; i++)
sub_mount_clear(s + i);
free(s);
}
static int sub_mount_compare(const SubMount *a, const SubMount *b) {
assert(a);
assert(b);
assert(a->path);
assert(b->path);
return path_compare(a->path, b->path);
}
static void sub_mount_drop(SubMount *s, size_t n) {
assert(s || n == 0);
for (size_t m = 0, i = 1; i < n; i++) {
if (path_startswith(s[i].path, s[m].path))
sub_mount_clear(s + i);
else
m = i;
}
}
int get_sub_mounts(const char *prefix, SubMount **ret_mounts, size_t *ret_n_mounts) {
_cleanup_(mnt_free_tablep) struct libmnt_table *table = NULL;
_cleanup_(mnt_free_iterp) struct libmnt_iter *iter = NULL;
SubMount *mounts = NULL;
size_t n = 0;
int r;
CLEANUP_ARRAY(mounts, n, sub_mount_array_free);
assert(prefix);
assert(ret_mounts);
assert(ret_n_mounts);
r = libmount_parse("/proc/self/mountinfo", NULL, &table, &iter);
if (r < 0)
return log_debug_errno(r, "Failed to parse /proc/self/mountinfo: %m");
for (;;) {
_cleanup_close_ int mount_fd = -EBADF;
_cleanup_free_ char *p = NULL;
struct libmnt_fs *fs;
const char *path;
int id1, id2;
r = mnt_table_next_fs(table, iter, &fs);
if (r == 1)
break; /* EOF */
if (r < 0)
return log_debug_errno(r, "Failed to get next entry from /proc/self/mountinfo: %m");
path = mnt_fs_get_target(fs);
if (!path)
continue;
if (isempty(path_startswith(path, prefix)))
continue;
id1 = mnt_fs_get_id(fs);
r = path_get_mnt_id(path, &id2);
if (r < 0) {
log_debug_errno(r, "Failed to get mount ID of '%s', ignoring: %m", path);
continue;
}
if (id1 != id2) {
/* The path may be hidden by another over-mount or already remounted. */
log_debug("The mount IDs of '%s' obtained by libmount and path_get_mnt_id() are different (%i vs %i), ignoring.",
path, id1, id2);
continue;
}
mount_fd = open(path, O_CLOEXEC|O_PATH);
if (mount_fd < 0) {
if (errno == ENOENT) /* The path may be hidden by another over-mount or already unmounted. */
continue;
return log_debug_errno(errno, "Failed to open subtree of mounted filesystem '%s': %m", path);
}
p = strdup(path);
if (!p)
return log_oom_debug();
if (!GREEDY_REALLOC(mounts, n + 1))
return log_oom_debug();
mounts[n++] = (SubMount) {
.path = TAKE_PTR(p),
.mount_fd = TAKE_FD(mount_fd),
};
}
typesafe_qsort(mounts, n, sub_mount_compare);
sub_mount_drop(mounts, n);
*ret_mounts = TAKE_PTR(mounts);
*ret_n_mounts = n;
return 0;
}
int bind_mount_submounts(
const char *source,
const char *target) {
SubMount *mounts = NULL;
size_t n = 0;
int ret = 0, r;
/* Bind mounts all child mounts of 'source' to 'target'. Useful when setting up a new procfs instance
* with new mount options to copy the original submounts over. */
assert(source);
assert(target);
CLEANUP_ARRAY(mounts, n, sub_mount_array_free);
r = get_sub_mounts(source, &mounts, &n);
if (r < 0)
return r;
FOREACH_ARRAY(m, mounts, n) {
_cleanup_free_ char *t = NULL;
const char *suffix;
if (isempty(m->path))
continue;
assert_se(suffix = path_startswith(m->path, source));
t = path_join(target, suffix);
if (!t)
return -ENOMEM;
r = path_is_mount_point(t);
if (r < 0) {
log_debug_errno(r, "Failed to detect if '%s' already is a mount point, ignoring: %m", t);
continue;
}
if (r > 0) {
log_debug("Not bind mounting '%s' from '%s' to '%s', since there's already a mountpoint.", suffix, source, target);
continue;
}
r = mount_follow_verbose(LOG_DEBUG, FORMAT_PROC_FD_PATH(m->mount_fd), t, NULL, MS_BIND|MS_REC, NULL);
if (r < 0 && ret == 0)
ret = r;
}
return ret;
}
int make_mount_point_inode_from_stat(const struct stat *st, const char *dest, mode_t mode) {
assert(st);
assert(dest);
if (S_ISDIR(st->st_mode))
return mkdir_label(dest, mode);
else
return RET_NERRNO(mknod(dest, S_IFREG|(mode & ~0111), 0));
}
int make_mount_point_inode_from_path(const char *source, const char *dest, mode_t mode) {
struct stat st;
assert(source);
assert(dest);
if (stat(source, &st) < 0)
return -errno;
return make_mount_point_inode_from_stat(&st, dest, mode);
}
int trigger_automount_at(int dir_fd, const char *path) {
_cleanup_free_ char *nested = NULL;
assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
nested = path_join(path, "a");
if (!nested)
return -ENOMEM;
(void) faccessat(dir_fd, nested, F_OK, 0);
return 0;
}
unsigned long credentials_fs_mount_flags(bool ro) {
/* A tight set of mount flags for credentials mounts */
return MS_NODEV|MS_NOEXEC|MS_NOSUID|ms_nosymfollow_supported()|(ro ? MS_RDONLY : 0);
}
int mount_credentials_fs(const char *path, size_t size, bool ro) {
_cleanup_free_ char *opts = NULL;
int r, noswap_supported;
/* Mounts a file system we can place credentials in, i.e. with tight access modes right from the
* beginning, and ideally swapping turned off. In order of preference:
*
* 1. tmpfs if it supports "noswap"
* 2. ramfs
* 3. tmpfs if it doesn't support "noswap"
*/
noswap_supported = mount_option_supported("tmpfs", "noswap", NULL); /* Check explicitly to avoid kmsg noise */
if (noswap_supported > 0) {
_cleanup_free_ char *noswap_opts = NULL;
if (asprintf(&noswap_opts, "mode=0700,nr_inodes=1024,size=%zu,noswap", size) < 0)
return -ENOMEM;
/* Best case: tmpfs with noswap (needs kernel >= 6.3) */
r = mount_nofollow_verbose(
LOG_DEBUG,
"tmpfs",
path,
"tmpfs",
credentials_fs_mount_flags(ro),
noswap_opts);
if (r >= 0)
return r;
}
r = mount_nofollow_verbose(
LOG_DEBUG,
"ramfs",
path,
"ramfs",
credentials_fs_mount_flags(ro),
"mode=0700");
if (r >= 0)
return r;
if (asprintf(&opts, "mode=0700,nr_inodes=1024,size=%zu", size) < 0)
return -ENOMEM;
return mount_nofollow_verbose(
LOG_DEBUG,
"tmpfs",
path,
"tmpfs",
credentials_fs_mount_flags(ro),
opts);
}
int make_fsmount(
int error_log_level,
const char *what,
const char *type,
unsigned long flags,
const char *options,
int userns_fd) {
_cleanup_close_ int fs_fd = -EBADF, mnt_fd = -EBADF;
_cleanup_free_ char *o = NULL;
unsigned long f;
int r;
assert(type);
assert(what);
r = mount_option_mangle(options, flags, &f, &o);
if (r < 0)
return log_full_errno(
error_log_level, r, "Failed to mangle mount options %s: %m",
strempty(options));
if (DEBUG_LOGGING) {
_cleanup_free_ char *fl = NULL;
(void) mount_flags_to_string(f, &fl);
log_debug("Creating mount fd for %s (%s) (%s \"%s\")...",
strna(what), strna(type), strnull(fl), strempty(o));
}
fs_fd = fsopen(type, FSOPEN_CLOEXEC);
if (fs_fd < 0)
return log_full_errno(error_log_level, errno, "Failed to open superblock for \"%s\": %m", type);
if (fsconfig(fs_fd, FSCONFIG_SET_STRING, "source", what, 0) < 0)
return log_full_errno(error_log_level, errno, "Failed to set mount source for \"%s\" to \"%s\": %m", type, what);
if (FLAGS_SET(f, MS_RDONLY))
if (fsconfig(fs_fd, FSCONFIG_SET_FLAG, "ro", NULL, 0) < 0)
return log_full_errno(error_log_level, errno, "Failed to set read only mount flag for \"%s\": %m", type);
for (const char *p = o;;) {
_cleanup_free_ char *word = NULL;
char *eq;
r = extract_first_word(&p, &word, ",", EXTRACT_KEEP_QUOTE);
if (r < 0)
return log_full_errno(error_log_level, r, "Failed to parse mount option string \"%s\": %m", o);
if (r == 0)
break;
eq = strchr(word, '=');
if (eq) {
*eq = 0;
eq++;
if (fsconfig(fs_fd, FSCONFIG_SET_STRING, word, eq, 0) < 0)
return log_full_errno(error_log_level, errno, "Failed to set mount option \"%s=%s\" for \"%s\": %m", word, eq, type);
} else {
if (fsconfig(fs_fd, FSCONFIG_SET_FLAG, word, NULL, 0) < 0)
return log_full_errno(error_log_level, errno, "Failed to set mount flag \"%s\" for \"%s\": %m", word, type);
}
}
if (fsconfig(fs_fd, FSCONFIG_CMD_CREATE, NULL, NULL, 0) < 0)
return log_full_errno(error_log_level, errno, "Failed to realize fs fd for \"%s\" (\"%s\"): %m", what, type);
mnt_fd = fsmount(fs_fd, FSMOUNT_CLOEXEC, 0);
if (mnt_fd < 0)
return log_full_errno(error_log_level, errno, "Failed to create mount fd for \"%s\" (\"%s\"): %m", what, type);
if (mount_setattr(mnt_fd, "", AT_EMPTY_PATH|AT_RECURSIVE,
&(struct mount_attr) {
.attr_set = ms_flags_to_mount_attr(f) | (userns_fd >= 0 ? MOUNT_ATTR_IDMAP : 0),
.userns_fd = userns_fd,
}, MOUNT_ATTR_SIZE_VER0) < 0)
return log_full_errno(error_log_level,
errno,
"Failed to set mount flags for \"%s\" (\"%s\"): %m",
what,
type);
return TAKE_FD(mnt_fd);
}
char* umount_and_unlink_and_free(char *p) {
if (!p)
return NULL;
PROTECT_ERRNO;
(void) umount2(p, 0);
(void) unlink(p);
return mfree(p);
}
static int path_get_mount_info_at(
int dir_fd,
const char *path,
char **ret_fstype,
char **ret_options) {
_cleanup_(mnt_free_tablep) struct libmnt_table *table = NULL;
_cleanup_(mnt_free_iterp) struct libmnt_iter *iter = NULL;
int r, mnt_id;
assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
r = path_get_mnt_id_at(dir_fd, path, &mnt_id);
if (r < 0)
return log_debug_errno(r, "Failed to get mount ID: %m");
r = libmount_parse("/proc/self/mountinfo", NULL, &table, &iter);
if (r < 0)
return log_debug_errno(r, "Failed to parse /proc/self/mountinfo: %m");
for (;;) {
struct libmnt_fs *fs;
r = mnt_table_next_fs(table, iter, &fs);
if (r == 1)
break; /* EOF */
if (r < 0)
return log_debug_errno(r, "Failed to get next entry from /proc/self/mountinfo: %m");
if (mnt_fs_get_id(fs) != mnt_id)
continue;
_cleanup_free_ char *fstype = NULL, *options = NULL;
if (ret_fstype) {
fstype = strdup(strempty(mnt_fs_get_fstype(fs)));
if (!fstype)
return log_oom_debug();
}
if (ret_options) {
options = strdup(strempty(mnt_fs_get_options(fs)));
if (!options)
return log_oom_debug();
}
if (ret_fstype)
*ret_fstype = TAKE_PTR(fstype);
if (ret_options)
*ret_options = TAKE_PTR(options);
return 0;
}
return log_debug_errno(SYNTHETIC_ERRNO(ESTALE), "Cannot find mount ID %i from /proc/self/mountinfo.", mnt_id);
}
int path_is_network_fs_harder_at(int dir_fd, const char *path) {
_cleanup_close_ int fd = -EBADF;
int r;
assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
fd = xopenat(dir_fd, path, O_PATH | O_CLOEXEC | O_NOFOLLOW);
if (fd < 0)
return fd;
r = fd_is_network_fs(fd);
if (r != 0)
return r;
_cleanup_free_ char *fstype = NULL, *options = NULL;
r = path_get_mount_info_at(fd, /* path = */ NULL, &fstype, &options);
if (r < 0)
return r;
if (fstype_is_network(fstype))
return true;
if (fstab_test_option(options, "_netdev\0"))
return true;
return false;
}
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