[PATCH 3.16 287/305] misc: mic: Fix for double fetch security bug in VOP driver

[Ben Hutchings]

3.16.37-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Ashutosh Dixit <ashutosh.dixit@xxxxxxxxx>

commit 9bf292bfca94694a721449e3fd752493856710f6 upstream.

The MIC VOP driver does two successive reads from user space to read a
variable length data structure. Kernel memory corruption can result if
the data structure changes between the two reads. This patch disallows
the chance of this happening.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=116651
Reported by: Pengfei Wang <wpengfeinudt@xxxxxxxxx>
Reviewed-by: Sudeep Dutt <sudeep.dutt@xxxxxxxxx>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.16:
 - Adjust filename, context
 - goto exit on failure]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/misc/mic/host/mic_virtio.c | 5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/misc/mic/host/mic_virtio.c
+++ b/drivers/misc/mic/host/mic_virtio.c
@@ -456,6 +456,11 @@ static int mic_copy_dp_entry(struct mic_
 			__func__, __LINE__, ret);
 		goto exit;
 	}
+	/* Ensure desc has not changed between the two reads */
+	if (memcmp(&dd, dd_config, sizeof(dd))) {
+		ret = -EINVAL;
+		goto exit;
+	}
 
 	vqconfig = mic_vq_config(dd_config);
 	for (i = 0; i < dd.num_vq; i++) {