sr: pass down correctly sized SCSI sense buffer

We're casting the CDROM layer request_sense to the SCSI sense
buffer, but the former is 64 bytes and the latter is 96 bytes.
As we generally allocate these on the stack, we end up blowing
up the stack.

Fix this by wrapping the scsi_execute() call with a properly
sized sense buffer, and copying back the bits for the CDROM
layer.

Cc: stable@vger.kernel.org
Reported-by: Piotr Gabriel Kosinski <pg.kosinski@gmail.com>
Reported-by: Daniel Shapira <daniel@twistlock.com>
Tested-by: Kees Cook <keescook@chromium.org>
Fixes: 82ed4db499 ("block: split scsi_request out of struct request")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/scsi/sr_ioctl.c

@@ -188,9 +188,13 @@ int sr_do_ioctl(Scsi_CD *cd, struct packet_command *cgc)
 	struct scsi_device *SDev;
 	struct scsi_sense_hdr sshdr;
 	int result, err = 0, retries = 0;
+	unsigned char sense_buffer[SCSI_SENSE_BUFFERSIZE], *senseptr = NULL;
 
 	SDev = cd->device;
 
+	if (cgc->sense)
+		senseptr = sense_buffer;
+
       retry:
 	if (!scsi_block_when_processing_errors(SDev)) {
 		err = -ENODEV;
@@ -198,10 +202,12 @@ int sr_do_ioctl(Scsi_CD *cd, struct packet_command *cgc)
 	}
 
 	result = scsi_execute(SDev, cgc->cmd, cgc->data_direction,
-			      cgc->buffer, cgc->buflen,
-			      (unsigned char *)cgc->sense, &sshdr,
+			      cgc->buffer, cgc->buflen, senseptr, &sshdr,
 			      cgc->timeout, IOCTL_RETRIES, 0, 0, NULL);
 
+	if (cgc->sense)
+		memcpy(cgc->sense, sense_buffer, sizeof(*cgc->sense));
+
 	/* Minimal error checking.  Ignore cases we know about, and report the rest. */
 	if (driver_byte(result) != 0) {
 		switch (sshdr.sense_key) {