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mount-util: use modern mount_setattr() syscall for bind_remount_one_with_mountinfo()

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New kernels have a nice syscall for changing bind mount flags. Let's use
it. This makes the complex libmount based iteration logic unnecessary.
This commit is contained in:
Lennart Poettering
2021-10-20 22:57:22 +02:00
parent 6dbfbc4667
commit 4f5644dba6
3 changed files with 51 additions and 0 deletions
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8
src/basic/missing_syscall.h
View File

@@ -465,10 +465,18 @@ struct mount_attr;
#define MOUNT_ATTR_IDMAP 0x00100000
#endif
#ifndef MOUNT_ATTR_NOSYMFOLLOW
#define MOUNT_ATTR_NOSYMFOLLOW 0x00200000
#endif
#ifndef AT_RECURSIVE
#define AT_RECURSIVE 0x8000
#endif
#ifndef MOUNT_ATTR_SIZE_VER0
#define MOUNT_ATTR_SIZE_VER0 32
#endif
static inline int missing_mount_setattr(
int dfd,
const char *path,

42
src/shared/mount-util.c
View File

@@ -134,6 +134,31 @@ int umount_recursive(const char *prefix, int flags) {
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(
@@ -374,6 +399,23 @@ int bind_remount_one_with_mountinfo(
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();

1
src/test/test-mount-util.c
View File

@@ -209,6 +209,7 @@ static void test_bind_remount_one(void) {
assert_se(fopen_unlocked("/proc/self/mountinfo", "re", &proc_self_mountinfo) >= 0);
assert_se(bind_remount_one_with_mountinfo("/run", MS_RDONLY, MS_RDONLY, proc_self_mountinfo) >= 0);
assert_se(bind_remount_one_with_mountinfo("/run", MS_NOEXEC, MS_RDONLY|MS_NOEXEC, proc_self_mountinfo) >= 0);
assert_se(bind_remount_one_with_mountinfo("/proc/idontexist", MS_RDONLY, MS_RDONLY, proc_self_mountinfo) == -ENOENT);
assert_se(bind_remount_one_with_mountinfo("/proc/self", MS_RDONLY, MS_RDONLY, proc_self_mountinfo) == -EINVAL);
assert_se(bind_remount_one_with_mountinfo("/", MS_RDONLY, MS_RDONLY, proc_self_mountinfo) >= 0);