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statmount: let unset strings be empty

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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>
This commit is contained in:
Miklos Szeredi 2025-01-30 13:15:00 +01:00 • committed by Christian Brauner
parent 4e7487245a
commit e52e97f09f
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GPG key ID: 91C61BC06578DCA2
1 changed files with 16 additions and 9 deletions
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25
fs/namespace.c
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@ -5191,39 +5191,45 @@ 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 = seq->count;
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 = start;
offp = &sm->fs_type;
ret = statmount_fs_type(s, seq);
break;
case STATMOUNT_MNT_ROOT:
sm->mnt_root = start;
offp = &sm->mnt_root;
ret = statmount_mnt_root(s, seq);
break;
case STATMOUNT_MNT_POINT:
sm->mnt_point = start;
offp = &sm->mnt_point;
ret = statmount_mnt_point(s, seq);
break;
case STATMOUNT_MNT_OPTS:
sm->mnt_opts = start;
offp = &sm->mnt_opts;
ret = statmount_mnt_opts(s, seq);
break;
case STATMOUNT_OPT_ARRAY:
sm->opt_array = start;
offp = &sm->opt_array;
ret = statmount_opt_array(s, seq);
break;
case STATMOUNT_OPT_SEC_ARRAY:
sm->opt_sec_array = start;
offp = &sm->opt_sec_array;
ret = statmount_opt_sec_array(s, seq);
break;
case STATMOUNT_FS_SUBTYPE:
sm->fs_subtype = start;
offp = &sm->fs_subtype;
statmount_fs_subtype(s, seq);
break;
case STATMOUNT_SB_SOURCE:
sm->sb_source = start;
offp = &sm->sb_source;
ret = statmount_sb_source(s, seq);
break;
default:
@ -5251,6 +5257,7 @@ static int statmount_string(struct kstatmount *s, u64 flag)
seq->buf[seq->count++] = '\0';
sm->mask |= flag;
*offp = start;
return 0;
}