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Date:   Sun, 14 Feb 2021 12:13:07 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Kees Cook <keescook@...omium.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>
Cc:     linux-kernel@...r.kernel.org,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        syzbot <syzbot+d0cf0ad6513e9a1da5df@...kaller.appspotmail.com>
Subject: [PATCH] pstore: fix warning in pstore_kill_sb()

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@...kaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.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

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