[PATCH 3.2 70/95] scsi: sr: Sanity check returned mode data

[Ben Hutchings <ben@decadent.org.uk>]

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

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

From: "Martin K. Petersen" <martin.petersen@oracle.com>

commit a00a7862513089f17209b732f230922f1942e0b9 upstream.

Kefeng Wang discovered that old versions of the QEMU CD driver would
return mangled mode data causing us to walk off the end of the buffer in
an attempt to parse it. Sanity check the returned mode sense data.

Reported-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 drivers/scsi/sr.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/scsi/sr.c
+++ b/drivers/scsi/sr.c
@@ -815,6 +815,7 @@ static void get_capabilities(struct scsi
 	unsigned char *buffer;
 	struct scsi_mode_data data;
 	struct scsi_sense_hdr sshdr;
+	unsigned int ms_len = 128;
 	int rc, n;
 
 	static const char *loadmech[] =
@@ -841,10 +842,11 @@ static void get_capabilities(struct scsi
 	scsi_test_unit_ready(cd->device, SR_TIMEOUT, MAX_RETRIES, &sshdr);
 
 	/* ask for mode page 0x2a */
-	rc = scsi_mode_sense(cd->device, 0, 0x2a, buffer, 128,
+	rc = scsi_mode_sense(cd->device, 0, 0x2a, buffer, ms_len,
 			     SR_TIMEOUT, 3, &data, NULL);
 
-	if (!scsi_status_is_good(rc)) {
+	if (!scsi_status_is_good(rc) || data.length > ms_len ||
+	    data.header_length + data.block_descriptor_length > data.length) {
 		/* failed, drive doesn't have capabilities mode page */
 		cd->cdi.speed = 1;
 		cd->cdi.mask |= (CDC_CD_R | CDC_CD_RW | CDC_DVD_R |