From: Miklos Szeredi Date: Thu, 30 Jan 2025 12:15:00 +0000 (+0100) Subject: statmount: let unset strings be empty X-Git-Tag: v6.12.14~3 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d49c64c1d723c167f521833f429ab28d3ca7e0d9;p=thirdparty%2Fkernel%2Fstable.git statmount: let unset strings be empty 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: 68385d77c05b ("statmount: simplify string option retrieval") Fixes: 46eae99ef733 ("add statmount(2) syscall") Cc: stable@vger.kernel.org # v6.8 Signed-off-by: Miklos Szeredi Link: https://lore.kernel.org/r/20250130121500.113446-1-mszeredi@redhat.com Reviewed-by: Jeff Layton Signed-off-by: Christian Brauner Signed-off-by: Greg Kroah-Hartman --- diff --git a/fs/namespace.c b/fs/namespace.c index 5e678b8c89ad1..73da51ac5a034 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -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; }