[PATCH v2 2/6] udp_vu: Check iov_tail_clone() return before assigning to msg_iovlen

[Jon Maloy <jmaloy@redhat.com>]

iov_tail_clone() returns ssize_t and can return -1 if the destination
iov array is too small. Its return value was assigned directly to
msg.msg_iovlen which is size_t, wrapping a negative value to a large
unsigned number passed to recvmsg().

Check for failure and return early, letting the caller rewind the
virtqueue.

Signed-off-by: Jon Maloy <jmaloy@redhat.com>

---
v2: Use if-guard instead of assert(), since the error path is
    a legitimate (if unlikely) condition handled by the caller.
---
 udp_vu.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/udp_vu.c b/udp_vu.c
index e4fb1057..edd9cae7 100644
--- a/udp_vu.c
+++ b/udp_vu.c
@@ -67,11 +67,15 @@ static ssize_t udp_vu_sock_recv(struct iov_tail *payload, size_t *cnt, int s)
 	struct iovec msg_iov[VIRTQUEUE_MAX_SIZE];
 	struct msghdr msg  = { 0 };
 	size_t iov_used;
+	ssize_t iovlen;
 	ssize_t dlen;
 
+	iovlen = iov_tail_clone(msg_iov, ARRAY_SIZE(msg_iov), payload);
+	if (iovlen < 0)
+		return -1;
+
 	msg.msg_iov = msg_iov;
-	msg.msg_iovlen = iov_tail_clone(msg.msg_iov, ARRAY_SIZE(msg_iov),
-					payload);
+	msg.msg_iovlen = iovlen;
 
 	/* read data from the socket */
 	dlen = recvmsg(s, &msg, 0);
-- 
2.52.0