[PATCH] pstore: fix warning in pstore_kill_sb()

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Kees Cook <keescook@chromium.org>,
	Anton Vorontsov <anton@enomsg.org>,
	Colin Cross <ccross@android.com>, Tony Luck <tony.luck@intel.com>
Cc: linux-kernel@vger.kernel.org,
	Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
	syzbot <syzbot+d0cf0ad6513e9a1da5df@syzkaller.appspotmail.com>
Subject: [PATCH] pstore: fix warning in pstore_kill_sb()
Date: Sun, 14 Feb 2021 12:13:07 +0900	[thread overview]
Message-ID: <20210214031307.57903-1-penguin-kernel@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <00000000000084130f05bb3aa802@google.com>

syzbot is hitting WARN_ON(pstore_sb != sb) at pstore_kill_sb() [1], for the
assumption that pstore_sb != NULL is wrong because pstore_fill_super() will
not assign pstore_sb = sb when new_inode() for d_make_root() returned NULL
(due to memory allocation fault injection).

Since mount_single() calls pstore_kill_sb() when pstore_fill_super()
failed, pstore_kill_sb() needs to be aware of such failure path.

[1] https://syzkaller.appspot.com/bug?id=6abacb8da5137cb47a416f2bef95719ed60508a0

Reported-by: syzbot <syzbot+d0cf0ad6513e9a1da5df@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
 fs/pstore/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
index 93a217e4f563..14658b009f1b 100644
--- a/fs/pstore/inode.c
+++ b/fs/pstore/inode.c
@@ -467,7 +467,7 @@ static struct dentry *pstore_mount(struct file_system_type *fs_type,
 static void pstore_kill_sb(struct super_block *sb)
 {
 	mutex_lock(&pstore_sb_lock);
-	WARN_ON(pstore_sb != sb);
+	WARN_ON(pstore_sb && pstore_sb != sb);
 
 	kill_litter_super(sb);
 	pstore_sb = NULL;
-- 
2.18.4

