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statmount: let unset strings be empty

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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>
This commit is contained in:
Miklos Szeredi
2025-01-30 13:15:00 +01:00
committed by Greg Kroah-Hartman
parent 7db0365ee6
commit d49c64c1d7
1 changed files with 12 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

16
fs/namespace.c
View File

@@ -5053,22 +5053,29 @@ 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;
case STATMOUNT_MNT_OPTS:
sm->mnt_opts = seq->count;
offp = &sm->mnt_opts;
ret = statmount_mnt_opts(s, seq);
break;
default:
@@ -5090,6 +5097,7 @@ static int statmount_string(struct kstatmount *s, u64 flag)
seq->buf[seq->count++] = '\0';
sm->mask |= flag;
*offp = start;
return 0;
}