sr: pass down correctly sized SCSI sense buffer

BugLink: https://bugs.launchpad.net/bugs/1811080

commit f7068114 upstream.

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.
Reported-by: Piotr Gabriel Kosinski <pg.kosinski@gmail.com>
Reported-by: Daniel Shapira <daniel@twistlock.com>
Tested-by: Kees Cook <keescook@chromium.org>
Fixes: 82ed4db4 ("block: split scsi_request out of struct request")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
[bwh: Despite what the "Fixes" field says, a buffer overrun was already
 possible if the sense data was really > 64 bytes long.
 Backported to 4.4:
 - We always need to allocate a sense buffer in order to call
   scsi_normalize_sense()
 - Remove the existing conditional heap-allocation of the sense buffer]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/scsi/sr_ioctl.c

@@ -187,30 +187,25 @@ 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;
-	struct request_sense *sense = cgc->sense;
+	unsigned char sense_buffer[SCSI_SENSE_BUFFERSIZE];
 
 	SDev = cd->device;
 
-	if (!sense) {
-		sense = kmalloc(SCSI_SENSE_BUFFERSIZE, GFP_KERNEL);
-		if (!sense) {
-			err = -ENOMEM;
-			goto out;
-		}
-	}
-
       retry:
 	if (!scsi_block_when_processing_errors(SDev)) {
 		err = -ENODEV;
 		goto out;
 	}
 
-	memset(sense, 0, sizeof(*sense));
+	memset(sense_buffer, 0, sizeof(sense_buffer));
 	result = scsi_execute(SDev, cgc->cmd, cgc->data_direction,
-			      cgc->buffer, cgc->buflen, (char *)sense,
+			      cgc->buffer, cgc->buflen, sense_buffer,
 			      cgc->timeout, IOCTL_RETRIES, 0, NULL);
 
-	scsi_normalize_sense((char *)sense, sizeof(*sense), &sshdr);
+	scsi_normalize_sense(sense_buffer, sizeof(sense_buffer), &sshdr);
+
+	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) {
@@ -261,8 +256,6 @@ int sr_do_ioctl(Scsi_CD *cd, struct packet_command *cgc)
 
 	/* Wake up a process waiting for device */
       out:
-	if (!cgc->sense)
-		kfree(sense);
 	cgc->stat = err;
 	return err;
 }