[PATCH] proc: s_fs_info may be NULL when proc_kill_sb is called

Alexey Gladkov
2020-06-10T13:05:57Z

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: fa10fed30f25 ("proc: allow to mount many instances of proc in one pid namespace")
Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
fs/proc/root.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/fs/proc/root.c b/fs/proc/root.c
index ffebed1999e5..a715eb9f196a 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -264,15 +264,18 @@ 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) {
+ if (fs_info->proc_self)
+ dput(fs_info->proc_self);

- if (fs_info->proc_thread_self)
- dput(fs_info->proc_thread_self);
+ if (fs_info->proc_thread_self)
+ dput(fs_info->proc_thread_self);
+
+ put_pid_ns(fs_info->pid_ns);
+ kfree(fs_info);
+ }

kill_anon_super(sb);
- put_pid_ns(fs_info->pid_ns);
- kfree(fs_info);
}

static struct file_system_type proc_fs_type = {
--
2.25.4