diff options
Diffstat (limited to 'hw/virtio-net.c')
| -rw-r--r-- | hw/virtio-net.c | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/hw/virtio-net.c b/hw/virtio-net.c index 61215b17e..409960f5e 100644 --- a/hw/virtio-net.c +++ b/hw/virtio-net.c @@ -154,6 +154,34 @@ static int virtio_net_can_receive(void *opaque) return 1; } +/* dhclient uses AF_PACKET but doesn't pass auxdata to the kernel so + * it never finds out that the packets don't have valid checksums. This + * causes dhclient to get upset. Fedora's carried a patch for ages to + * fix this with Xen but it hasn't appeared in an upstream release of + * dhclient yet. + * + * To avoid breaking existing guests, we catch udp packets and add + * checksums. This is terrible but it's better than hacking the guest + * kernels. + * + * N.B. if we introduce a zero-copy API, this operation is no longer free so + * we should provide a mechanism to disable it to avoid polluting the host + * cache. + */ +static void work_around_broken_dhclient(struct virtio_net_hdr *hdr, + const uint8_t *buf, size_t size) +{ + if ((hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) && /* missing csum */ + (size > 27 && size < 1500) && /* normal sized MTU */ + (buf[12] == 0x08 && buf[13] == 0x00) && /* ethertype == IPv4 */ + (buf[23] == 17) && /* ip.protocol == UDP */ + (buf[34] == 0 && buf[35] == 67)) { /* udp.srcport == bootps */ + /* FIXME this cast is evil */ + net_checksum_calculate((uint8_t *)buf, size); + hdr->flags &= ~VIRTIO_NET_HDR_F_NEEDS_CSUM; + } +} + static void virtio_net_receive(void *opaque, const uint8_t *buf, int size) { VirtIONet *n = opaque; @@ -180,6 +208,7 @@ static void virtio_net_receive(void *opaque, const uint8_t *buf, int size) if (tap_has_vnet_hdr(n->vc->vlan->first_client)) { memcpy(hdr, buf, sizeof(*hdr)); offset += total; + work_around_broken_dhclient(hdr, buf + offset, size - offset); } /* copy in packet. ugh */ |