scsi: sr: Sanity check returned mode data

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.

Cc: <stable@vger.kernel.org>
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>

diff --git a/drivers/scsi/sr.c b/drivers/scsi/sr.c
index 0b29b9329b1c2f5c8207188884498f314e0a414a..a8f630213a1a0fce250e23b00a9452676389b159 100644 (file)
--- a/drivers/scsi/sr.c
+++ b/drivers/scsi/sr.c
@@ -836,6 +836,7 @@ static void get_capabilities(struct scsi_cd *cd)
        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[] =
@@ -862,10 +863,11 @@ static void get_capabilities(struct scsi_cd *cd)
        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 |