proc: s_fs_info may be NULL when proc_kill_sb is called

syzbot found that proc_fill_super() fails before filling up sb->s_fs_info,
deactivate_locked_super() will be called and sb->s_fs_info will be NULL.
The proc_kill_sb() does not expect fs_info to be NULL which is wrong.

Link: https://lore.kernel.org/lkml/0000000000002d7ca605a7b8b1c5@google.com
Reported-by: syzbot+4abac52934a48af5ff19@syzkaller.appspotmail.com
Fixes: 7a66ed4baee9 ("proc: allow to mount many instances of proc in one pid namespace")
Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

diff --git a/fs/proc/root.c b/fs/proc/root.c
index ffebed1999e500cb529c4d3dd44a33f7bfe09556..5e444d4f9717fb32ca43900d7d5824f998ef9b0a 100644 (file)
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -264,11 +264,13 @@ static void proc_kill_sb(struct super_block *sb)
 {
        struct proc_fs_info *fs_info = proc_sb_info(sb);
 
-       if (fs_info->proc_self)
-               dput(fs_info->proc_self);
+       if (!fs_info) {
+               kill_anon_super(sb);
+               return;
+       }
 
-       if (fs_info->proc_thread_self)
-               dput(fs_info->proc_thread_self);
+       dput(fs_info->proc_self);
+       dput(fs_info->proc_thread_self);
 
        kill_anon_super(sb);
        put_pid_ns(fs_info->pid_ns);