On 17/10/2024 02:10, Stefano Brivio wrote:
+/**
+ * tcp_vu_prepare() - Prepare the packet header
+ * @c: Execution context
+ * @conn: Connection pointer
+ * @first: Pointer to the array of IO vectors
+ * @dlen: Packet data length
+ * @check: Checksum, if already known
+ */
+static void tcp_vu_prepare(const struct ctx *c,
+ struct tcp_tap_conn *conn, struct iovec *first,
+ size_t dlen, const uint16_t **check)
+{
+ const struct flowside *toside = TAPFLOW(conn);
+ char *base = first->iov_base;
+ struct ethhdr *eh;
+
+ /* we guess the first iovec provided by the guest can embed
+ * all the headers needed by L2 frame
+ */
What happens if it doesn't (buggy guest)? Do we have a way to make
sure
it's the case? I guess it's more straightforward to do this in
tcp_vu_data_from_sock() where we check and set iov_len (even though the
implication of VIRTIO_NET_F_MRG_RXBUF isn't totally clear to me).
According to spec, minimum size of a buffer is 1526 bytes
(
https://docs.oasis-open.org/virtio/virtio/v1.2/csd01/virtio-v1.2-csd01.html…)
So if the guest is buggy, we will write in the guest memory out of the (buggy) provided
buffer, and we can crash the guest. But it's what happens to a buggy guest.
We can't fix the guest, IMO passt should crash in this case (add an ASSERT()?).