can: isotp: support MSG_TRUNC flag when reading from socket

BugLink: https://bugs.launchpad.net/bugs/1968984 [ Upstream commit 42bf50a ] When providing the MSG_TRUNC flag via recvmsg() syscall the return value provides the real length of the packet or datagram, even when it was longer than the passed buffer. Fixes: e057dd3 ("can: add ISO 15765-2:2016 transport protocol") Link: linux-can/can-utils#347 (comment) Link: https://lore.kernel.org/all/[email protected] Suggested-by: Derek Will <[email protected]> Signed-off-by: Oliver Hartkopp <[email protected]> Signed-off-by: Marc Kleine-Budde <[email protected]> Signed-off-by: Sasha Levin <[email protected]> Signed-off-by: Andrea Righi <[email protected]>
AlexGhiti · Apr 14, 2022 · dea776f · dea776f
1 parent d9ee949
commit dea776f
Showing 1 changed file with 15 additions and 12 deletions.
diff --git a/net/can/isotp.c b/net/can/isotp.c
@@ -1006,29 +1006,28 @@ static int isotp_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
 	struct sock *sk = sock->sk;
 	struct sk_buff *skb;
 	struct isotp_sock *so = isotp_sk(sk);
-	int err = 0;
-	int noblock;
+	int noblock = flags & MSG_DONTWAIT;
+	int ret = 0;
 
-	noblock = flags & MSG_DONTWAIT;
-	flags &= ~MSG_DONTWAIT;
+	if (flags & ~(MSG_DONTWAIT | MSG_TRUNC))
+		return -EINVAL;
 
 	if (!so->bound)
 		return -EADDRNOTAVAIL;
 
-	skb = skb_recv_datagram(sk, flags, noblock, &err);
+	flags &= ~MSG_DONTWAIT;
+	skb = skb_recv_datagram(sk, flags, noblock, &ret);
 	if (!skb)
-		return err;
+		return ret;
 
 	if (size < skb->len)
 		msg->msg_flags |= MSG_TRUNC;
 	else
 		size = skb->len;
 
-	err = memcpy_to_msg(msg, skb->data, size);
-	if (err < 0) {
-		skb_free_datagram(sk, skb);
-		return err;
-	}
+	ret = memcpy_to_msg(msg, skb->data, size);
+	if (ret < 0)
+		goto out_err;
 
 	sock_recv_timestamp(msg, sk, skb);
 
@@ -1038,9 +1037,13 @@ static int isotp_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
 		memcpy(msg->msg_name, skb->cb, msg->msg_namelen);
 	}
 
+	/* set length of return value */
+	ret = (flags & MSG_TRUNC) ? skb->len : size;
+
+out_err:
 	skb_free_datagram(sk, skb);
 
-	return size;
+	return ret;
 }
 
 static int isotp_release(struct socket *sock)