linux-kernel - [PATCH] freevxfs: set bp to NULL after dropping its reference in loop

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Date:   Sun, 25 Nov 2018 09:49:17 +0800
From:   Pan Bian <bianpan2016@....com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Pan Bian <bianpan2016@....com>
Subject: [PATCH] freevxfs: set bp to NULL after dropping its reference in loop

The function vxfs_bmap_indir calls brelse(bh) in the loop and tries to
start the next iteration. However, if it happens to break the loop,
brelse(bp) will be called again. Resulting in a potential double free
bug. This patch assigns NULL to bh after dropping its reference in the
loop body.

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

diff --git a/fs/freevxfs/vxfs_bmap.c b/fs/freevxfs/vxfs_bmap.c
index 1fd41cf..136e5d1 100644
--- a/fs/freevxfs/vxfs_bmap.c
+++ b/fs/freevxfs/vxfs_bmap.c
@@ -150,6 +150,7 @@ vxfs_bmap_indir(struct inode *ip, long indir, int size, long block)
 
 		if (block < off) {
 			brelse(bp);
+			bp = NULL;
 			continue;
 		}
 
@@ -186,6 +187,7 @@ vxfs_bmap_indir(struct inode *ip, long indir, int size, long block)
 			BUG();
 		}
 		brelse(bp);
+		bp = NULL;
 	}
 
 fail:
-- 
2.7.4