Received-SPF: pass (google.com: domain of linux-ext4-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Jan Kara <jack@suse.cz>
To:     Ted Tso <tytso@mit.edu>
Cc:     <linux-ext4@vger.kernel.org>, Jan Kara <jack@suse.cz>,
        syzbot+628472a2aac693ab0fcd@syzkaller.appspotmail.com,
        stable@vger.kernel.org
Subject: [PATCH] ext4: Fix timer use-after-free on failed mount
Date:   Mon, 15 Mar 2021 17:59:06 +0100
Message-Id: <20210315165906.2175-1-jack@suse.cz>
MIME-Version: 1.0
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Precedence: bulk

When filesystem mount fails because of corrupted filesystem we first
cancel the s_err_report timer reminding fs errors every day and only
then we flush s_error_work. However s_error_work may report another fs
error and re-arm timer thus resulting in timer use-after-free. Fix the
problem by first flushing the work and only after that canceling the
s_err_report timer.

Reported-by: syzbot+628472a2aac693ab0fcd@syzkaller.appspotmail.com
Fixes: 2d01ddc86606 ("ext4: save error info to sb through journal if available")
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index ad34a37278cd..2e3d4c5c2eb4 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5149,8 +5149,8 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 failed_mount3a:
 	ext4_es_unregister_shrinker(sbi);
 failed_mount3:
-	del_timer_sync(&sbi->s_err_report);
 	flush_work(&sbi->s_error_work);
+	del_timer_sync(&sbi->s_err_report);
 	if (sbi->s_mmp_tsk)
 		kthread_stop(sbi->s_mmp_tsk);
 failed_mount2:
-- 
2.26.2