From: Miklos Szeredi <mszeredi@xxxxxxxxxx> 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@xxxxxxxxxxxxxx/ Fixes: 68385d77c05b ("statmount: simplify string option retrieval") Fixes: 46eae99ef733 ("add statmount(2) syscall") Cc: stable@xxxxxxxxxxxxxxx # v6.8 Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx> Link: https://lore.kernel.org/r/20250130121500.113446-1-mszeredi@xxxxxxxxxx Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx> Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/namespace.c | 25 ++++++++++++++++--------- 1 file changed, 16 insertions(+), 9 deletions(-) --- a/fs/namespace.c +++ b/fs/namespace.c @@ -5137,39 +5137,45 @@ static int statmount_string(struct kstat 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: @@ -5197,6 +5203,7 @@ static int statmount_string(struct kstat seq->buf[seq->count++] = '\0'; sm->mask |= flag; + *offp = start; return 0; } Patches currently in stable-queue which might be from mszeredi@xxxxxxxxxx are queue-6.13/statmount-let-unset-strings-be-empty.patch
