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From:   Pan Bian <bianpan2016@163.com>
To:     linux-kernel@vger.kernel.org
Cc:     Kai Bankett <chaosman@ontika.net>, Pan Bian <bianpan2016@163.com>
Subject: [PATCH] fs/qnx6: set and bh1 and bh2 to NULL after dropping references
Date:   Mon, 26 Nov 2018 10:21:28 +0800
Message-Id: <1543198888-36464-1-git-send-email-bianpan2016@163.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

The function qnx6_fill_super drops the reference to bh2 when superblock
1 is activated via brelse, otherwise it drops the reference to bh1 when
superblock 2 is activated. If error occurs after that, it will try to
drop the references to bh1 and bh2 again. This may result in
use-after-free bugs. The patch sets bh1 and bh2 to NULL after their
reference counts are decreased.

Signed-off-by: Pan Bian <bianpan2016@163.com>
---
 fs/qnx6/inode.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/qnx6/inode.c b/fs/qnx6/inode.c
index 4aeb26b..e8a8536 100644
--- a/fs/qnx6/inode.c
+++ b/fs/qnx6/inode.c
@@ -405,12 +405,14 @@ static int qnx6_fill_super(struct super_block *s, void *data, int silent)
 		sbi->sb_buf = bh1;
 		sbi->sb = (struct qnx6_super_block *)bh1->b_data;
 		brelse(bh2);
+		bh2 = NULL;
 		pr_info("superblock #1 active\n");
 	} else {
 		/* superblock #2 active */
 		sbi->sb_buf = bh2;
 		sbi->sb = (struct qnx6_super_block *)bh2->b_data;
 		brelse(bh1);
+		bh1 = NULL;
 		pr_info("superblock #2 active\n");
 	}
 mmi_success:
-- 
2.7.4