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systemd/src/core/exec-credential.c
Zbigniew Jędrzejewski-Szmek 1743b8bad1 core/exec-credential: downgrade warning about missing cred to debug 
Follow-up for 6b34871f5d.

The general idea is that the list of credentials to load can and will specify
credentials which actually aren't provided, so a warning is too much. Let's
downgrade this to "info". If it turns out to be too noisy, we can downgrade
further in the future.
2024-05-14 20:13:57 +02:00

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/* SPDX-License-Identifier: LGPL-2.1-or-later */
#include <sys/mount.h>
#include "acl-util.h"
#include "creds-util.h"
#include "exec-credential.h"
#include "execute.h"
#include "fileio.h"
#include "glob-util.h"
#include "io-util.h"
#include "iovec-util.h"
#include "label-util.h"
#include "mkdir-label.h"
#include "mount-util.h"
#include "mount.h"
#include "mountpoint-util.h"
#include "process-util.h"
#include "random-util.h"
#include "recurse-dir.h"
#include "rm-rf.h"
#include "tmpfile-util.h"
ExecSetCredential *exec_set_credential_free(ExecSetCredential *sc) {
if (!sc)
return NULL;
free(sc->id);
free(sc->data);
return mfree(sc);
}
ExecLoadCredential *exec_load_credential_free(ExecLoadCredential *lc) {
if (!lc)
return NULL;
free(lc->id);
free(lc->path);
return mfree(lc);
}
DEFINE_HASH_OPS_WITH_VALUE_DESTRUCTOR(
exec_set_credential_hash_ops,
char, string_hash_func, string_compare_func,
ExecSetCredential, exec_set_credential_free);
DEFINE_HASH_OPS_WITH_VALUE_DESTRUCTOR(
exec_load_credential_hash_ops,
char, string_hash_func, string_compare_func,
ExecLoadCredential, exec_load_credential_free);
bool exec_params_need_credentials(const ExecParameters *p) {
assert(p);
return p->flags & (EXEC_SETUP_CREDENTIALS|EXEC_SETUP_CREDENTIALS_FRESH);
}
bool exec_context_has_credentials(const ExecContext *c) {
assert(c);
return !hashmap_isempty(c->set_credentials) ||
!hashmap_isempty(c->load_credentials) ||
!set_isempty(c->import_credentials);
}
bool exec_context_has_encrypted_credentials(const ExecContext *c) {
assert(c);
const ExecLoadCredential *load_cred;
HASHMAP_FOREACH(load_cred, c->load_credentials)
if (load_cred->encrypted)
return true;
const ExecSetCredential *set_cred;
HASHMAP_FOREACH(set_cred, c->set_credentials)
if (set_cred->encrypted)
return true;
return false;
}
static int get_credential_directory(
const char *runtime_prefix,
const char *unit,
char **ret) {
char *p;
assert(ret);
if (!runtime_prefix || !unit) {
*ret = NULL;
return 0;
}
p = path_join(runtime_prefix, "credentials", unit);
if (!p)
return -ENOMEM;
*ret = p;
return 1;
}
int exec_context_get_credential_directory(
const ExecContext *context,
const ExecParameters *params,
const char *unit,
char **ret) {
assert(context);
assert(params);
assert(unit);
assert(ret);
if (!exec_params_need_credentials(params) || !exec_context_has_credentials(context)) {
*ret = NULL;
return 0;
}
return get_credential_directory(params->prefix[EXEC_DIRECTORY_RUNTIME], unit, ret);
}
int unit_add_default_credential_dependencies(Unit *u, const ExecContext *c) {
_cleanup_free_ char *p = NULL, *m = NULL;
int r;
assert(u);
assert(c);
if (!exec_context_has_credentials(c))
return 0;
/* Let's make sure the credentials directory of this service is unmounted *after* the service itself
* shuts down. This only matters if mount namespacing is not used for the service, and hence the
* credentials mount appears on the host. */
r = get_credential_directory(u->manager->prefix[EXEC_DIRECTORY_RUNTIME], u->id, &p);
if (r <= 0)
return r;
r = unit_name_from_path(p, ".mount", &m);
if (r < 0)
return r;
return unit_add_dependency_by_name(u, UNIT_AFTER, m, /* add_reference= */ true, UNIT_DEPENDENCY_FILE);
}
int exec_context_destroy_credentials(Unit *u) {
_cleanup_free_ char *p = NULL;
int r;
assert(u);
r = get_credential_directory(u->manager->prefix[EXEC_DIRECTORY_RUNTIME], u->id, &p);
if (r <= 0)
return r;
/* This is either a tmpfs/ramfs of its own, or a plain directory. Either way, let's first try to
* unmount it, and afterwards remove the mount point */
if (umount2(p, MNT_DETACH|UMOUNT_NOFOLLOW) >= 0)
(void) mount_invalidate_state_by_path(u->manager, p);
(void) rm_rf(p, REMOVE_ROOT|REMOVE_CHMOD);
return 0;
}
static int write_credential(
int dfd,
const char *id,
const void *data,
size_t size,
uid_t uid,
gid_t gid,
bool ownership_ok) {
_cleanup_(unlink_and_freep) char *tmp = NULL;
_cleanup_close_ int fd = -EBADF;
int r;
assert(dfd >= 0);
assert(id);
assert(data || size == 0);
r = tempfn_random_child("", "cred", &tmp);
if (r < 0)
return r;
fd = openat(dfd, tmp, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL|O_NOFOLLOW|O_NOCTTY, 0600);
if (fd < 0) {
tmp = mfree(tmp);
return -errno;
}
r = loop_write(fd, data, size);
if (r < 0)
return r;
if (fchmod(fd, 0400) < 0) /* Take away "w" bit */
return -errno;
if (uid_is_valid(uid) && uid != getuid()) {
r = fd_add_uid_acl_permission(fd, uid, ACL_READ);
if (r < 0) {
if (!ERRNO_IS_NOT_SUPPORTED(r) && !ERRNO_IS_PRIVILEGE(r))
return r;
if (!ownership_ok) /* Ideally we use ACLs, since we can neatly express what we want
* to express: that the user gets read access and nothing
* else. But if the backing fs can't support that (e.g. ramfs)
* then we can use file ownership instead. But that's only safe if
* we can then re-mount the whole thing read-only, so that the
* user can no longer chmod() the file to gain write access. */
return r;
if (fchown(fd, uid, gid) < 0)
return -errno;
}
}
if (renameat(dfd, tmp, dfd, id) < 0)
return -errno;
tmp = mfree(tmp);
return 0;
}
typedef enum CredentialSearchPath {
CREDENTIAL_SEARCH_PATH_TRUSTED,
CREDENTIAL_SEARCH_PATH_ENCRYPTED,
CREDENTIAL_SEARCH_PATH_ALL,
_CREDENTIAL_SEARCH_PATH_MAX,
_CREDENTIAL_SEARCH_PATH_INVALID = -EINVAL,
} CredentialSearchPath;
static char **credential_search_path(const ExecParameters *params, CredentialSearchPath path) {
_cleanup_strv_free_ char **l = NULL;
assert(params);
assert(path >= 0 && path < _CREDENTIAL_SEARCH_PATH_MAX);
/* Assemble a search path to find credentials in. For non-encrypted credentials, We'll look in
* /etc/credstore/ (and similar directories in /usr/lib/ + /run/). If we're looking for encrypted
* credentials, we'll look in /etc/credstore.encrypted/ (and similar dirs). */
if (IN_SET(path, CREDENTIAL_SEARCH_PATH_ENCRYPTED, CREDENTIAL_SEARCH_PATH_ALL)) {
if (strv_extend(&l, params->received_encrypted_credentials_directory) < 0)
return NULL;
if (strv_extend_strv(&l, CONF_PATHS_STRV("credstore.encrypted"), /* filter_duplicates= */ true) < 0)
return NULL;
}
if (IN_SET(path, CREDENTIAL_SEARCH_PATH_TRUSTED, CREDENTIAL_SEARCH_PATH_ALL)) {
if (strv_extend(&l, params->received_credentials_directory) < 0)
return NULL;
if (strv_extend_strv(&l, CONF_PATHS_STRV("credstore"), /* filter_duplicates= */ true) < 0)
return NULL;
}
if (DEBUG_LOGGING) {
_cleanup_free_ char *t = strv_join(l, ":");
log_debug("Credential search path is: %s", strempty(t));
}
return TAKE_PTR(l);
}
static int maybe_decrypt_and_write_credential(
int dir_fd,
const char *id,
bool encrypted,
uid_t uid,
gid_t gid,
bool ownership_ok,
const char *data,
size_t size,
uint64_t *left) {
_cleanup_(iovec_done_erase) struct iovec plaintext = {};
size_t add;
int r;
assert(dir_fd >= 0);
assert(id);
assert(left);
if (encrypted) {
r = decrypt_credential_and_warn(
id,
now(CLOCK_REALTIME),
/* tpm2_device= */ NULL,
/* tpm2_signature_path= */ NULL,
getuid(),
&IOVEC_MAKE(data, size),
CREDENTIAL_ANY_SCOPE,
&plaintext);
if (r < 0)
return r;
data = plaintext.iov_base;
size = plaintext.iov_len;
}
add = strlen(id) + size;
if (add > *left)
return -E2BIG;
r = write_credential(dir_fd, id, data, size, uid, gid, ownership_ok);
if (r < 0)
return log_debug_errno(r, "Failed to write credential '%s': %m", id);
*left -= add;
return 0;
}
static int load_credential_glob(
const char *path,
bool encrypted,
char * const *search_path,
ReadFullFileFlags flags,
int write_dfd,
uid_t uid,
gid_t gid,
bool ownership_ok,
uint64_t *left) {
int r;
assert(path);
assert(search_path);
assert(write_dfd >= 0);
assert(left);
STRV_FOREACH(d, search_path) {
_cleanup_globfree_ glob_t pglob = {};
_cleanup_free_ char *j = NULL;
j = path_join(*d, path);
if (!j)
return -ENOMEM;
r = safe_glob(j, 0, &pglob);
if (r == -ENOENT)
continue;
if (r < 0)
return r;
FOREACH_ARRAY(p, pglob.gl_pathv, pglob.gl_pathc) {
_cleanup_free_ char *fn = NULL;
_cleanup_(erase_and_freep) char *data = NULL;
size_t size;
/* path is absolute, hence pass AT_FDCWD as nop dir fd here */
r = read_full_file_full(
AT_FDCWD,
*p,
UINT64_MAX,
encrypted ? CREDENTIAL_ENCRYPTED_SIZE_MAX : CREDENTIAL_SIZE_MAX,
flags,
NULL,
&data, &size);
if (r < 0)
return log_debug_errno(r, "Failed to read credential '%s': %m", *p);
r = path_extract_filename(*p, &fn);
if (r < 0)
return log_debug_errno(r, "Failed to extract filename from '%s': %m", *p);
r = maybe_decrypt_and_write_credential(
write_dfd,
fn,
encrypted,
uid,
gid,
ownership_ok,
data, size,
left);
if (r == -EEXIST)
continue;
if (r < 0)
return r;
}
}
return 0;
}
static int load_credential(
const ExecContext *context,
const ExecParameters *params,
const char *id,
const char *path,
bool encrypted,
const char *unit,
int read_dfd,
int write_dfd,
uid_t uid,
gid_t gid,
bool ownership_ok,
uint64_t *left) {
ReadFullFileFlags flags = READ_FULL_FILE_SECURE|READ_FULL_FILE_FAIL_WHEN_LARGER;
_cleanup_strv_free_ char **search_path = NULL;
_cleanup_(erase_and_freep) char *data = NULL;
_cleanup_free_ char *bindname = NULL;
const char *source = NULL;
bool missing_ok = true;
size_t size, maxsz;
int r;
assert(context);
assert(params);
assert(id);
assert(path);
assert(unit);
assert(read_dfd >= 0 || read_dfd == AT_FDCWD);
assert(write_dfd >= 0);
assert(left);
if (read_dfd >= 0) {
/* If a directory fd is specified, then read the file directly from that dir. In this case we
* won't do AF_UNIX stuff (we simply don't want to recursively iterate down a tree of AF_UNIX
* IPC sockets). It's OK if a file vanishes here in the time we enumerate it and intend to
* open it. */
if (!filename_is_valid(path)) /* safety check */
return -EINVAL;
missing_ok = true;
source = path;
} else if (path_is_absolute(path)) {
/* If this is an absolute path, read the data directly from it, and support AF_UNIX
* sockets */
if (!path_is_valid(path)) /* safety check */
return -EINVAL;
flags |= READ_FULL_FILE_CONNECT_SOCKET;
/* Pass some minimal info about the unit and the credential name we are looking to acquire
* via the source socket address in case we read off an AF_UNIX socket. */
if (asprintf(&bindname, "@%" PRIx64 "/unit/%s/%s", random_u64(), unit, id) < 0)
return -ENOMEM;
missing_ok = false;
source = path;
} else if (credential_name_valid(path)) {
/* If this is a relative path, take it as credential name relative to the credentials
* directory we received ourselves. We don't support the AF_UNIX stuff in this mode, since we
* are operating on a credential store, i.e. this is guaranteed to be regular files. */
search_path = credential_search_path(params, CREDENTIAL_SEARCH_PATH_ALL);
if (!search_path)
return -ENOMEM;
missing_ok = true;
} else
source = NULL;
if (encrypted)
flags |= READ_FULL_FILE_UNBASE64;
maxsz = encrypted ? CREDENTIAL_ENCRYPTED_SIZE_MAX : CREDENTIAL_SIZE_MAX;
if (search_path)
STRV_FOREACH(d, search_path) {
_cleanup_free_ char *j = NULL;
j = path_join(*d, path);
if (!j)
return -ENOMEM;
r = read_full_file_full(
AT_FDCWD, j, /* path is absolute, hence pass AT_FDCWD as nop dir fd here */
UINT64_MAX,
maxsz,
flags,
NULL,
&data, &size);
if (r != -ENOENT)
break;
}
else if (source)
r = read_full_file_full(
read_dfd, source,
UINT64_MAX,
maxsz,
flags,
bindname,
&data, &size);
else
r = -ENOENT;
if (r == -ENOENT && (missing_ok || hashmap_contains(context->set_credentials, id))) {
/* Make a missing inherited credential non-fatal, let's just continue. After all apps
* will get clear errors if we don't pass such a missing credential on as they
* themselves will get ENOENT when trying to read them, which should not be much
* worse than when we handle the error here and make it fatal.
*
* Also, if the source file doesn't exist, but a fallback is set via SetCredentials=
* we are fine, too. */
log_full_errno(hashmap_contains(context->set_credentials, id) ? LOG_DEBUG : LOG_INFO,
r, "Couldn't read inherited credential '%s', skipping: %m", path);
return 0;
}
if (r < 0)
return log_debug_errno(r, "Failed to read credential '%s': %m", path);
return maybe_decrypt_and_write_credential(write_dfd, id, encrypted, uid, gid, ownership_ok, data, size, left);
}
struct load_cred_args {
const ExecContext *context;
const ExecParameters *params;
bool encrypted;
const char *unit;
int dfd;
uid_t uid;
gid_t gid;
bool ownership_ok;
uint64_t *left;
};
static int load_cred_recurse_dir_cb(
RecurseDirEvent event,
const char *path,
int dir_fd,
int inode_fd,
const struct dirent *de,
const struct statx *sx,
void *userdata) {
struct load_cred_args *args = ASSERT_PTR(userdata);
_cleanup_free_ char *sub_id = NULL;
int r;
assert(path);
assert(de);
if (event != RECURSE_DIR_ENTRY)
return RECURSE_DIR_CONTINUE;
if (!IN_SET(de->d_type, DT_REG, DT_SOCK))
return RECURSE_DIR_CONTINUE;
sub_id = strreplace(path, "/", "_");
if (!sub_id)
return -ENOMEM;
if (!credential_name_valid(sub_id))
return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), "Credential would get ID %s, which is not valid, refusing", sub_id);
if (faccessat(args->dfd, sub_id, F_OK, AT_SYMLINK_NOFOLLOW) >= 0) {
log_debug("Skipping credential with duplicated ID %s at %s", sub_id, path);
return RECURSE_DIR_CONTINUE;
}
if (errno != ENOENT)
return log_debug_errno(errno, "Failed to test if credential %s exists: %m", sub_id);
r = load_credential(
args->context,
args->params,
sub_id,
de->d_name,
args->encrypted,
args->unit,
dir_fd,
args->dfd,
args->uid,
args->gid,
args->ownership_ok,
args->left);
if (r < 0)
return r;
return RECURSE_DIR_CONTINUE;
}
static int acquire_credentials(
const ExecContext *context,
const ExecParameters *params,
const char *unit,
const char *p,
uid_t uid,
gid_t gid,
bool ownership_ok) {
uint64_t left = CREDENTIALS_TOTAL_SIZE_MAX;
_cleanup_close_ int dfd = -EBADF;
const char *ic;
ExecLoadCredential *lc;
ExecSetCredential *sc;
int r;
assert(context);
assert(params);
assert(unit);
assert(p);
dfd = open(p, O_DIRECTORY|O_CLOEXEC);
if (dfd < 0)
return -errno;
r = fd_acl_make_writable(dfd); /* Add the "w" bit, if we are reusing an already set up credentials dir where it was unset */
if (r < 0)
return r;
/* First, load credentials off disk (or acquire via AF_UNIX socket) */
HASHMAP_FOREACH(lc, context->load_credentials) {
_cleanup_close_ int sub_fd = -EBADF;
/* If this is an absolute path, then try to open it as a directory. If that works, then we'll
* recurse into it. If it is an absolute path but it isn't a directory, then we'll open it as
* a regular file. Finally, if it's a relative path we will use it as a credential name to
* propagate a credential passed to us from further up. */
if (path_is_absolute(lc->path)) {
sub_fd = open(lc->path, O_DIRECTORY|O_CLOEXEC|O_RDONLY);
if (sub_fd < 0 && !IN_SET(errno,
ENOTDIR, /* Not a directory */
ENOENT)) /* Doesn't exist? */
return log_debug_errno(errno, "Failed to open '%s': %m", lc->path);
}
if (sub_fd < 0)
/* Regular file (incl. a credential passed in from higher up) */
r = load_credential(
context,
params,
lc->id,
lc->path,
lc->encrypted,
unit,
AT_FDCWD,
dfd,
uid,
gid,
ownership_ok,
&left);
else
/* Directory */
r = recurse_dir(sub_fd,
/* path= */ lc->id, /* recurse_dir() will suffix the subdir paths from here to the top-level id */
/* statx_mask= */ 0,
/* n_depth_max= */ UINT_MAX,
RECURSE_DIR_SORT|RECURSE_DIR_IGNORE_DOT|RECURSE_DIR_ENSURE_TYPE,
load_cred_recurse_dir_cb,
&(struct load_cred_args) {
.context = context,
.params = params,
.encrypted = lc->encrypted,
.unit = unit,
.dfd = dfd,
.uid = uid,
.gid = gid,
.ownership_ok = ownership_ok,
.left = &left,
});
if (r < 0)
return r;
}
/* Next, look for system credentials and credentials in the credentials store. Note that these do not
* override any credentials found earlier. */
SET_FOREACH(ic, context->import_credentials) {
_cleanup_free_ char **search_path = NULL;
search_path = credential_search_path(params, CREDENTIAL_SEARCH_PATH_TRUSTED);
if (!search_path)
return -ENOMEM;
r = load_credential_glob(
ic,
/* encrypted = */ false,
search_path,
READ_FULL_FILE_SECURE|READ_FULL_FILE_FAIL_WHEN_LARGER,
dfd,
uid,
gid,
ownership_ok,
&left);
if (r < 0)
return r;
search_path = strv_free(search_path);
search_path = credential_search_path(params, CREDENTIAL_SEARCH_PATH_ENCRYPTED);
if (!search_path)
return -ENOMEM;
r = load_credential_glob(
ic,
/* encrypted = */ true,
search_path,
READ_FULL_FILE_SECURE|READ_FULL_FILE_FAIL_WHEN_LARGER|READ_FULL_FILE_UNBASE64,
dfd,
uid,
gid,
ownership_ok,
&left);
if (r < 0)
return r;
}
/* Finally, we add in literally specified credentials. If the credentials already exist, we'll not
* add them, so that they can act as a "default" if the same credential is specified multiple times. */
HASHMAP_FOREACH(sc, context->set_credentials) {
_cleanup_(iovec_done_erase) struct iovec plaintext = {};
const char *data;
size_t size, add;
/* Note that we check ahead of time here instead of relying on O_EXCL|O_CREAT later to return
* EEXIST if the credential already exists. That's because the TPM2-based decryption is kinda
* slow and involved, hence it's nice to be able to skip that if the credential already
* exists anyway. */
if (faccessat(dfd, sc->id, F_OK, AT_SYMLINK_NOFOLLOW) >= 0)
continue;
if (errno != ENOENT)
return log_debug_errno(errno, "Failed to test if credential %s exists: %m", sc->id);
if (sc->encrypted) {
r = decrypt_credential_and_warn(
sc->id,
now(CLOCK_REALTIME),
/* tpm2_device= */ NULL,
/* tpm2_signature_path= */ NULL,
getuid(),
&IOVEC_MAKE(sc->data, sc->size),
CREDENTIAL_ANY_SCOPE,
&plaintext);
if (r < 0)
return r;
data = plaintext.iov_base;
size = plaintext.iov_len;
} else {
data = sc->data;
size = sc->size;
}
add = strlen(sc->id) + size;
if (add > left)
return -E2BIG;
r = write_credential(dfd, sc->id, data, size, uid, gid, ownership_ok);
if (r < 0)
return r;
left -= add;
}
r = fd_acl_make_read_only(dfd); /* Now take away the "w" bit */
if (r < 0)
return r;
/* After we created all keys with the right perms, also make sure the credential store as a whole is
* accessible */
if (uid_is_valid(uid) && uid != getuid()) {
r = fd_add_uid_acl_permission(dfd, uid, ACL_READ | ACL_EXECUTE);
if (r < 0) {
if (!ERRNO_IS_NOT_SUPPORTED(r) && !ERRNO_IS_PRIVILEGE(r))
return r;
if (!ownership_ok)
return r;
if (fchown(dfd, uid, gid) < 0)
return -errno;
}
}
return 0;
}
static int setup_credentials_internal(
const ExecContext *context,
const ExecParameters *params,
const char *unit,
const char *final, /* This is where the credential store shall eventually end up at */
const char *workspace, /* This is where we can prepare it before moving it to the final place */
bool reuse_workspace, /* Whether to reuse any existing workspace mount if it already is a mount */
bool must_mount, /* Whether to require that we mount something, it's not OK to use the plain directory fall back */
uid_t uid,
gid_t gid) {
bool final_mounted;
int r, workspace_mounted; /* negative if we don't know yet whether we have/can mount something; true
* if we mounted something; false if we definitely can't mount anything */
assert(context);
assert(params);
assert(unit);
assert(final);
assert(workspace);
r = path_is_mount_point(final);
if (r < 0)
return r;
final_mounted = r > 0;
if (final_mounted) {
if (FLAGS_SET(params->flags, EXEC_SETUP_CREDENTIALS_FRESH)) {
r = umount_verbose(LOG_DEBUG, final, MNT_DETACH|UMOUNT_NOFOLLOW);
if (r < 0)
return r;
final_mounted = false;
} else {
/* We can reuse the previous credential dir */
r = dir_is_empty(final, /* ignore_hidden_or_backup = */ false);
if (r < 0)
return r;
if (r == 0) {
log_debug("Credential dir for unit '%s' already set up, skipping.", unit);
return 0;
}
}
}
if (reuse_workspace) {
r = path_is_mount_point(workspace);
if (r < 0)
return r;
if (r > 0)
workspace_mounted = true; /* If this is already a mount, and we are supposed to reuse
* it, let's keep this in mind */
else
workspace_mounted = -1; /* We need to figure out if we can mount something to the workspace */
} else
workspace_mounted = -1; /* ditto */
/* If both the final place and the workspace are mounted, we have no mounts to set up, based on
* the assumption that they're actually the same tmpfs (but the latter with MS_RDONLY different).
* If the workspace is not mounted, we just bind the final place over and make it writable. */
must_mount = must_mount || final_mounted;
if (workspace_mounted < 0) {
if (!final_mounted)
/* Nothing is mounted on the workspace yet, let's try to mount a new tmpfs if
* not using the final place. */
r = mount_credentials_fs(workspace, CREDENTIALS_TOTAL_SIZE_MAX, /* ro= */ false);
if (final_mounted || r < 0) {
/* If using final place or failed to mount new tmpfs, make a bind mount from
* the final to the workspace, so that we can make it writable there. */
r = mount_nofollow_verbose(LOG_DEBUG, final, workspace, NULL, MS_BIND|MS_REC, NULL);
if (r < 0) {
if (!ERRNO_IS_PRIVILEGE(r))
/* Propagate anything that isn't a permission problem. */
return r;
if (must_mount)
/* If it's not OK to use the plain directory fallback, propagate all
* errors too. */
return r;
/* If we lack privileges to bind mount stuff, then let's gracefully proceed
* for compat with container envs, and just use the final dir as is.
* Final place must not be mounted in this case (refused by must_mount
* above) */
workspace_mounted = false;
} else {
/* Make the new bind mount writable (i.e. drop MS_RDONLY) */
r = mount_nofollow_verbose(LOG_DEBUG,
NULL,
workspace,
NULL,
MS_BIND|MS_REMOUNT|credentials_fs_mount_flags(/* ro= */ false),
NULL);
if (r < 0)
return r;
workspace_mounted = true;
}
} else
workspace_mounted = true;
}
assert(workspace_mounted >= 0);
assert(!must_mount || workspace_mounted);
const char *where = workspace_mounted ? workspace : final;
(void) label_fix_full(AT_FDCWD, where, final, 0);
r = acquire_credentials(context, params, unit, where, uid, gid, workspace_mounted);
if (r < 0) {
/* If we're using final place as workspace, and failed to acquire credentials, we might
* have left half-written creds there. Let's get rid of the whole mount, so future
* calls won't reuse it. */
if (final_mounted)
(void) umount_verbose(LOG_DEBUG, final, MNT_DETACH|UMOUNT_NOFOLLOW);
return r;
}
if (workspace_mounted) {
if (!final_mounted) {
/* Make workspace read-only now, so that any bind mount we make from it defaults to
* read-only too */
r = mount_nofollow_verbose(LOG_DEBUG, NULL, workspace, NULL, MS_BIND|MS_REMOUNT|credentials_fs_mount_flags(/* ro= */ true), NULL);
if (r < 0)
return r;
/* And mount it to the final place, read-only */
r = mount_nofollow_verbose(LOG_DEBUG, workspace, final, NULL, MS_MOVE, NULL);
} else
/* Otherwise we just get rid of the bind mount of final place */
r = umount_verbose(LOG_DEBUG, workspace, MNT_DETACH|UMOUNT_NOFOLLOW);
if (r < 0)
return r;
} else {
_cleanup_free_ char *parent = NULL;
/* If we do not have our own mount put used the plain directory fallback, then we need to
* open access to the top-level credential directory and the per-service directory now */
r = path_extract_directory(final, &parent);
if (r < 0)
return r;
if (chmod(parent, 0755) < 0)
return -errno;
}
return 0;
}
int exec_setup_credentials(
const ExecContext *context,
const ExecParameters *params,
const char *unit,
uid_t uid,
gid_t gid) {
_cleanup_free_ char *p = NULL, *q = NULL;
int r;
assert(context);
assert(params);
assert(unit);
if (!exec_params_need_credentials(params) || !exec_context_has_credentials(context))
return 0;
if (!params->prefix[EXEC_DIRECTORY_RUNTIME])
return -EINVAL;
/* This is where we'll place stuff when we are done; the main credentials directory is world-readable,
* and the subdir we mount over with a read-only file system readable by the service's user. */
q = path_join(params->prefix[EXEC_DIRECTORY_RUNTIME], "credentials");
if (!q)
return -ENOMEM;
r = mkdir_label(q, 0755); /* top-level dir: world readable/searchable */
if (r < 0 && r != -EEXIST)
return r;
p = path_join(q, unit);
if (!p)
return -ENOMEM;
r = mkdir_label(p, 0700); /* per-unit dir: private to user */
if (r < 0 && r != -EEXIST)
return r;
r = safe_fork("(sd-mkdcreds)", FORK_DEATHSIG_SIGTERM|FORK_WAIT|FORK_NEW_MOUNTNS, NULL);
if (r < 0) {
_cleanup_(rmdir_and_freep) char *u = NULL; /* remove the temporary workspace if we can */
_cleanup_free_ char *t = NULL;
/* If this is not a privilege or support issue then propagate the error */
if (!ERRNO_IS_NOT_SUPPORTED(r) && !ERRNO_IS_PRIVILEGE(r))
return r;
/* Temporary workspace, that remains inaccessible all the time. We prepare stuff there before moving
* it into place, so that users can't access half-initialized credential stores. */
t = path_join(params->prefix[EXEC_DIRECTORY_RUNTIME], "systemd/temporary-credentials");
if (!t)
return -ENOMEM;
/* We can't set up a mount namespace. In that case operate on a fixed, inaccessible per-unit
* directory outside of /run/credentials/ first, and then move it over to /run/credentials/
* after it is fully set up */
u = path_join(t, unit);
if (!u)
return -ENOMEM;
FOREACH_STRING(i, t, u) {
r = mkdir_label(i, 0700);
if (r < 0 && r != -EEXIST)
return r;
}
r = setup_credentials_internal(
context,
params,
unit,
p, /* final mount point */
u, /* temporary workspace to overmount */
true, /* reuse the workspace if it is already a mount */
false, /* it's OK to fall back to a plain directory if we can't mount anything */
uid,
gid);
if (r < 0)
return r;
} else if (r == 0) {
/* We managed to set up a mount namespace, and are now in a child. That's great. In this case
* we can use the same directory for all cases, after turning off propagation. Question
* though is: where do we turn off propagation exactly, and where do we place the workspace
* directory? We need some place that is guaranteed to be a mount point in the host, and
* which is guaranteed to have a subdir we can mount over. /run/ is not suitable for this,
* since we ultimately want to move the resulting file system there, i.e. we need propagation
* for /run/ eventually. We could use our own /run/systemd/bind mount on itself, but that
* would be visible in the host mount table all the time, which we want to avoid. Hence, what
* we do here instead we use /dev/ and /dev/shm/ for our purposes. We know for sure that
* /dev/ is a mount point and we now for sure that /dev/shm/ exists. Hence we can turn off
* propagation on the former, and then overmount the latter.
*
* Yes it's nasty playing games with /dev/ and /dev/shm/ like this, since it does not exist
* for this purpose, but there are few other candidates that work equally well for us, and
* given that we do this in a privately namespaced short-lived single-threaded process that
* no one else sees this should be OK to do. */
/* Turn off propagation from our namespace to host */
r = mount_nofollow_verbose(LOG_DEBUG, NULL, "/dev", NULL, MS_SLAVE|MS_REC, NULL);
if (r < 0)
goto child_fail;
r = setup_credentials_internal(
context,
params,
unit,
p, /* final mount point */
"/dev/shm", /* temporary workspace to overmount */
false, /* do not reuse /dev/shm if it is already a mount, under no circumstances */
true, /* insist that something is mounted, do not allow fallback to plain directory */
uid,
gid);
if (r < 0)
goto child_fail;
_exit(EXIT_SUCCESS);
child_fail:
_exit(EXIT_FAILURE);
}
/* If the credentials dir is empty and not a mount point, then there's no point in having it. Let's
* try to remove it. This matters in particular if we created the dir as mount point but then didn't
* actually end up mounting anything on it. In that case we'd rather have ENOENT than EACCESS being
* seen by users when trying access this inode. */
(void) rmdir(p);
return 0;
}
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