[PULL V2 26/44] hw/net/net_tx_pkt: Check the payload length

[Jason Wang <jasowang@redhat.com>]

From: Akihiko Odaki <akihiko.odaki@daynix.com>

Check the payload length if checksumming to ensure the payload contains
the space for the resulting value.

This bug was found by Alexander Bulekov with the fuzzer:
https://patchew.org/QEMU/20230129053316.1071513-1-alxndr@bu.edu/

The fixed test case is:
fuzz/crash_6aeaa33e7211ecd603726c53e834df4c6d1e08bc

Fixes: e263cd49c7 ("Packet abstraction for VMWARE network devices")
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 hw/net/net_tx_pkt.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/hw/net/net_tx_pkt.c b/hw/net/net_tx_pkt.c
index 4a35e84..986a3ad 100644
--- a/hw/net/net_tx_pkt.c
+++ b/hw/net/net_tx_pkt.c
@@ -342,11 +342,17 @@ bool net_tx_pkt_build_vheader(struct NetTxPkt *pkt, bool tso_enable,
     if (csum_enable) {
         switch (pkt->l4proto) {
         case IP_PROTO_TCP:
+            if (pkt->payload_len < sizeof(struct tcp_hdr)) {
+                return false;
+            }
             pkt->virt_hdr.flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;
             pkt->virt_hdr.csum_start = pkt->hdr_len;
             pkt->virt_hdr.csum_offset = offsetof(struct tcp_hdr, th_sum);
             break;
         case IP_PROTO_UDP:
+            if (pkt->payload_len < sizeof(struct udp_hdr)) {
+                return false;
+            }
             pkt->virt_hdr.flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;
             pkt->virt_hdr.csum_start = pkt->hdr_len;
             pkt->virt_hdr.csum_offset = offsetof(struct udp_hdr, uh_sum);
-- 
2.7.4