linux-kernel - [PATCH 4.9 195/206] xfs: dont crash if reading a directory results in an unexpected hole

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Date:   Tue, 10 Jan 2017 14:37:58 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dave Chinner <dchinner@...hat.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>
Subject: [PATCH 4.9 195/206] xfs: dont crash if reading a directory results in an unexpected hole

4.9-stable review patch.  If anyone has any objections, please let me know.

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


From: "Darrick J. Wong" <darrick.wong@...cle.com>

commit 96a3aefb8ffde23180130460b0b2407b328eb727 upstream.

In xfs_dir3_data_read, we can encounter the situation where err == 0 and
*bpp == NULL if the given bno offset happens to be a hole; this leads to
a crash if we try to set the buffer type after the _da_read_buf call.
Holes can happen due to corrupt or malicious entries in the bmbt data,
so be a little more careful when we're handling buffers.

Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
Reviewed-by: Dave Chinner <dchinner@...hat.com>
Signed-off-by: Dave Chinner <david@...morbit.com>
Cc: Christoph Hellwig <hch@....de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/xfs/libxfs/xfs_dir2_data.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/xfs/libxfs/xfs_dir2_data.c
+++ b/fs/xfs/libxfs/xfs_dir2_data.c
@@ -329,7 +329,7 @@ xfs_dir3_data_read(
 
 	err = xfs_da_read_buf(tp, dp, bno, mapped_bno, bpp,
 				XFS_DATA_FORK, &xfs_dir3_data_buf_ops);
-	if (!err && tp)
+	if (!err && tp && *bpp)
 		xfs_trans_buf_set_type(tp, *bpp, XFS_BLFT_DIR_DATA_BUF);
 	return err;
 }