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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Pan Bian <bianpan2016@163.com>,
        Jan Kara <jack@suse.cz>
Subject: [PATCH 4.19 118/139] ext2: fix potential use after free
Date:   Tue,  4 Dec 2018 11:49:59 +0100
Message-Id: <20181204103655.510462440@linuxfoundation.org>
In-Reply-To: <20181204103649.950154335@linuxfoundation.org>
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4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Pan Bian <bianpan2016@163.com>

commit ecebf55d27a11538ea84aee0be643dd953f830d5 upstream.

The function ext2_xattr_set calls brelse(bh) to drop the reference count
of bh. After that, bh may be freed. However, following brelse(bh),
it reads bh->b_data via macro HDR(bh). This may result in a
use-after-free bug. This patch moves brelse(bh) after reading field.

CC: stable@vger.kernel.org
Signed-off-by: Pan Bian <bianpan2016@163.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/ext2/xattr.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/ext2/xattr.c
+++ b/fs/ext2/xattr.c
@@ -612,9 +612,9 @@ skip_replace:
 	}
 
 cleanup:
-	brelse(bh);
 	if (!(bh && header == HDR(bh)))
 		kfree(header);
+	brelse(bh);
 	up_write(&EXT2_I(inode)->xattr_sem);
 
 	return error;