spi/spidev: check message size before copying

Message size needs to be checked before copying, or bad things could
happen.

Signed-off-by: Domen Puncer <domen.puncer@telargo.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/spi/spidev.c

@@ -168,6 +168,12 @@ static int spidev_message(struct spidev_data *spidev,
 			n--, k_tmp++, u_tmp++) {
 		k_tmp->len = u_tmp->len;
 
+		total += k_tmp->len;
+		if (total > bufsiz) {
+			status = -EMSGSIZE;
+			goto done;
+		}
+
 		if (u_tmp->rx_buf) {
 			k_tmp->rx_buf = buf;
 			if (!access_ok(VERIFY_WRITE, u_tmp->rx_buf, u_tmp->len))
@@ -179,12 +185,6 @@ static int spidev_message(struct spidev_data *spidev,
 					u_tmp->len))
 				goto done;
 		}
-
-		total += k_tmp->len;
-		if (total > bufsiz) {
-			status = -EMSGSIZE;
-			goto done;
-		}
 		buf += k_tmp->len;
 
 		k_tmp->cs_change = !!u_tmp->cs_change;