[SCSI] Return VPD page length in scsi_vpd_inquiry()

We should be returning the number of bytes of the
requested VPD page in scsi_vpd_inquiry.
This makes it easier for the caller to verify the
required space.

[jejb: fix up mm warning spotted by Sergey]
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/scsi.c

@@ -942,14 +942,17 @@ EXPORT_SYMBOL(scsi_track_queue_full);
  * This is an internal helper function.  You probably want to use
  * scsi_get_vpd_page instead.
  *
- * Returns 0 on success or a negative error number.
+ * Returns size of the vpd page on success or a negative error number.
  */
 static int scsi_vpd_inquiry(struct scsi_device *sdev, unsigned char *buffer,
 							u8 page, unsigned len)
 {
 	int result;
 	unsigned char cmd[16];
 
+	if (len < 4)
+		return -EINVAL;
+
 	cmd[0] = INQUIRY;
 	cmd[1] = 1;		/* EVPD */
 	cmd[2] = page;
@@ -964,13 +967,13 @@ static int scsi_vpd_inquiry(struct scsi_device *sdev, unsigned char *buffer,
 	result = scsi_execute_req(sdev, cmd, DMA_FROM_DEVICE, buffer,
 				  len, NULL, 30 * HZ, 3, NULL);
 	if (result)
-		return result;
+		return -EIO;
 
 	/* Sanity check that we got the page back that we asked for */
 	if (buffer[1] != page)
 		return -EIO;
 
-	return 0;
+	return get_unaligned_be16(&buffer[2]) + 4;
 }
 
 /**
@@ -997,26 +1000,26 @@ int scsi_get_vpd_page(struct scsi_device *sdev, u8 page, unsigned char *buf,
 
 	/* Ask for all the pages supported by this device */
 	result = scsi_vpd_inquiry(sdev, buf, 0, buf_len);
-	if (result)
+	if (result < 4)
 		goto fail;
 
 	/* If the user actually wanted this page, we can skip the rest */
 	if (page == 0)
 		return 0;
 
-	for (i = 0; i < min((int)buf[3], buf_len - 4); i++)
-		if (buf[i + 4] == page)
+	for (i = 4; i < min(result, buf_len); i++)
+		if (buf[i] == page)
 			goto found;
 
-	if (i < buf[3] && i >= buf_len - 4)
+	if (i < result && i >= buf_len)
 		/* ran off the end of the buffer, give us benefit of doubt */
 		goto found;
 	/* The device claims it doesn't support the requested page */
 	goto fail;
 
  found:
 	result = scsi_vpd_inquiry(sdev, buf, page, buf_len);
-	if (result)
+	if (result < 0)
 		goto fail;
 
 	return 0;