diff mbox series

[Stable-8.2.6,02/18] virtio-net: drop too short packets early

Message ID 20240704155251.1481617-2-mjt@tls.msk.ru
State New
Headers show
Series [Stable-8.2.6,01/18] target/i386: fix size of EBP writeback in gen_enter() | expand

Commit Message

Michael Tokarev July 4, 2024, 3:52 p.m. UTC 
From: Alexey Dobriyan <adobriyan@yandex-team.ru>

Reproducer from https://gitlab.com/qemu-project/qemu/-/issues/1451
creates small packet (1 segment, len = 10 == n->guest_hdr_len),
then destroys queue.

"if (n->host_hdr_len != n->guest_hdr_len)" is triggered, if body creates
zero length/zero segment packet as there is nothing after guest header.

qemu_sendv_packet_async() tries to send it.

slirp discards it because it is smaller than Ethernet header,
but returns 0 because tx hooks are supposed to return total length of data.

0 is propagated upwards and is interpreted as "packet has been sent"
which is terrible because queue is being destroyed, nobody is waiting for TX
to complete and assert it triggered.

Fix is discard such empty packets instead of sending them.

Length 1 packets will go via different codepath:

	virtqueue_push(q->tx_vq, elem, 0);
	virtio_notify(vdev, q->tx_vq);
	g_free(elem);

and aren't problematic.

Signed-off-by: Alexey Dobriyan <adobriyan@yandex-team.ru>
Signed-off-by: Jason Wang <jasowang@redhat.com>
(cherry picked from commit 2c3e4e2de699cd4d9f6c71f30a22d8f125cd6164)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
diff mbox series

Patch

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 8451dbee41..0467b3bd8a 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -2709,18 +2709,14 @@  static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
         out_sg = elem->out_sg;
         if (out_num < 1) {
             virtio_error(vdev, "virtio-net header not in first element");
-            virtqueue_detach_element(q->tx_vq, elem, 0);
-            g_free(elem);
-            return -EINVAL;
+            goto detach;
         }
 
         if (n->has_vnet_hdr) {
             if (iov_to_buf(out_sg, out_num, 0, &vhdr, n->guest_hdr_len) <
                 n->guest_hdr_len) {
                 virtio_error(vdev, "virtio-net header incorrect");
-                virtqueue_detach_element(q->tx_vq, elem, 0);
-                g_free(elem);
-                return -EINVAL;
+                goto detach;
             }
             if (n->needs_vnet_hdr_swap) {
                 virtio_net_hdr_swap(vdev, (void *) &vhdr);
@@ -2751,6 +2747,11 @@  static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
                              n->guest_hdr_len, -1);
             out_num = sg_num;
             out_sg = sg;
+
+            if (out_num < 1) {
+                virtio_error(vdev, "virtio-net nothing to send");
+                goto detach;
+            }
         }
 
         ret = qemu_sendv_packet_async(qemu_get_subqueue(n->nic, queue_index),
@@ -2771,6 +2772,11 @@  drop:
         }
     }
     return num_packets;
+
+detach:
+    virtqueue_detach_element(q->tx_vq, elem, 0);
+    g_free(elem);
+    return -EINVAL;
 }
 
 static void virtio_net_tx_timer(void *opaque);