can: Fix copy_from_user() results interpretation

Both copy_to_ and _from_user return the number of bytes, that failed to
reach their destination, not the 0/-EXXX values.

Based on patch from Pavel Emelyanov <xemul@openvz.org>

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Oliver Hartkopp <oliver.hartkopp@volkswagen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/can/raw.c

@@ -435,15 +435,13 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
 			if (!filter)
 				return -ENOMEM;
 
-			err = copy_from_user(filter, optval, optlen);
-			if (err) {
+			if (copy_from_user(filter, optval, optlen)) {
 				kfree(filter);
-				return err;
+				return -EFAULT;
 			}
 		} else if (count == 1) {
-			err = copy_from_user(&sfilter, optval, optlen);
-			if (err)
-				return err;
+			if (copy_from_user(&sfilter, optval, optlen))
+				return -EFAULT;
 		}
 
 		lock_sock(sk);
@@ -493,9 +491,8 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
 		if (optlen != sizeof(err_mask))
 			return -EINVAL;
 
-		err = copy_from_user(&err_mask, optval, optlen);
-		if (err)
-			return err;
+		if (copy_from_user(&err_mask, optval, optlen))
+			return -EFAULT;
 
 		err_mask &= CAN_ERR_MASK;
 
@@ -531,7 +528,8 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
 		if (optlen != sizeof(ro->loopback))
 			return -EINVAL;
 
-		err = copy_from_user(&ro->loopback, optval, optlen);
+		if (copy_from_user(&ro->loopback, optval, optlen))
+			return -EFAULT;
 
 		break;
 
@@ -539,7 +537,8 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
 		if (optlen != sizeof(ro->recv_own_msgs))
 			return -EINVAL;
 
-		err = copy_from_user(&ro->recv_own_msgs, optval, optlen);
+		if (copy_from_user(&ro->recv_own_msgs, optval, optlen))
+			return -EFAULT;
 
 		break;