net: qrtr: Fix an out of bounds read qrtr_endpoint_post()

This code assumes that the user passed in enough data for a
qrtr_hdr_v1 or qrtr_hdr_v2 struct, but it's not necessarily true.  If
the buffer is too small then it will read beyond the end.
Reported-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reported-by: syzbot+b8fe393f999a291a9ea6@syzkaller.appspotmail.com
Fixes: 194ccc88 ("net: qrtr: Support decoding incoming v2 packets")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/qrtr/qrtr.c

@@ -429,7 +429,7 @@ int qrtr_endpoint_post(struct qrtr_endpoint *ep, const void *data, size_t len)
 	unsigned int ver;
 	size_t hdrlen;
 
-	if (len & 3)
+	if (len == 0 || len & 3)
 		return -EINVAL;
 
 	skb = netdev_alloc_skb(NULL, len);
@@ -443,6 +443,8 @@ int qrtr_endpoint_post(struct qrtr_endpoint *ep, const void *data, size_t len)
 
 	switch (ver) {
 	case QRTR_PROTO_VER_1:
+		if (len < sizeof(*v1))
+			goto err;
 		v1 = data;
 		hdrlen = sizeof(*v1);
 
@@ -456,6 +458,8 @@ int qrtr_endpoint_post(struct qrtr_endpoint *ep, const void *data, size_t len)
 		size = le32_to_cpu(v1->size);
 		break;
 	case QRTR_PROTO_VER_2:
+		if (len < sizeof(*v2))
+			goto err;
 		v2 = data;
 		hdrlen = sizeof(*v2) + v2->optlen;