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statmount: let unset strings be empty

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BugLink: https://bugs.launchpad.net/bugs/2114239

commit e52e97f09fb66fd868260d05bd6b74a9a3db39ee upstream.

Just like it's normal for unset values to be zero, unset strings should be
empty instead of containing random values.

It seems to be a typical mistake that the mask returned by statmount is not
checked, which can result in various bugs.

With this fix, these bugs are prevented, since it is highly likely that
userspace would just want to turn the missing mask case into an empty
string anyway (most of the recently found cases are of this type).

Link: https://lore.kernel.org/all/CAJfpegsVCPfCn2DpM8iiYSS5DpMsLB8QBUCHecoj6s0Vxf4jzg@mail.gmail.com/
Fixes: 68385d77c0 ("statmount: simplify string option retrieval")
Fixes: 46eae99ef7 ("add statmount(2) syscall")
Cc: stable@vger.kernel.org # v6.8
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Link: https://lore.kernel.org/r/20250130121500.113446-1-mszeredi@redhat.com
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[nwager: Drop hunk due to missing commit:
f9af549d1fd3 ("fs: export mount options via statmount()")]
Signed-off-by: Noah Wager <noah.wager@canonical.com>
Signed-off-by: Mehmet Basaran <mehmet.basaran@canonical.com>
This commit is contained in:
Miklos Szeredi
2025-01-30 13:15:00 +01:00
committed by Mehmet Basaran
parent 79a95c2aa7
commit b2e191abc0
1 changed files with 11 additions and 3 deletions
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fs/namespace.c
+11 -3
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@@ -4855,18 +4855,25 @@ static int statmount_string(struct kstatmount *s, u64 flag)
size_t kbufsize;
struct seq_file *seq = &s->seq;
struct statmount *sm = &s->sm;
u32 start, *offp;
/* Reserve an empty string at the beginning for any unset offsets */
if (!seq->count)
seq_putc(seq, 0);
start = seq->count;
switch (flag) {
case STATMOUNT_FS_TYPE:
sm->fs_type = seq->count;
offp = &sm->fs_type;
ret = statmount_fs_type(s, seq);
break;
case STATMOUNT_MNT_ROOT:
sm->mnt_root = seq->count;
offp = &sm->mnt_root;
ret = statmount_mnt_root(s, seq);
break;
case STATMOUNT_MNT_POINT:
sm->mnt_point = seq->count;
offp = &sm->mnt_point;
ret = statmount_mnt_point(s, seq);
break;
default:
@@ -4888,6 +4895,7 @@ static int statmount_string(struct kstatmount *s, u64 flag)
seq->buf[seq->count++] = '\0';
sm->mask |= flag;
*offp = start;
return 0;
}