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net: be more gentle about silly gso requests coming from user 

Recent change in virtio_net_hdr_to_skb() broke some packetdrill tests.

When --mss=XXX option is set, packetdrill always provide gso_type & gso_size
for its inbound packets, regardless of packet size.

	if (packet->tcp && packet->mss) {
		if (packet->ipv4)
			gso.gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
		else
			gso.gso_type = VIRTIO_NET_HDR_GSO_TCPV6;
		gso.gso_size = packet->mss;
	}

Since many other programs could do the same, relax virtio_net_hdr_to_skb()
to no longer return an error, but instead ignore gso settings.

This keeps Willem intent to make sure no malicious packet could
reach gso stack.

Note that TCP stack has a special logic in tcp_set_skb_tso_segs()
to clear gso_size for small packets.

Fixes: 6dd912f826 ("net: check untrusted gso_size at kernel entry")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2020-05-28 14:57:47 -07:00 committed by David S. Miller
parent 45ebf73ebc
commit 7c6d2ecbda
1 changed files with 9 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
include/linux/virtio_net.h
View File

@ -109,16 +109,17 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
u16 gso_size = __virtio16_to_cpu(little_endian, hdr->gso_size);
struct skb_shared_info *shinfo = skb_shinfo(skb);
if (skb->len - p_off <= gso_size)
return -EINVAL;
/* Too small packets are not really GSO ones. */
if (skb->len - p_off > gso_size) {
shinfo->gso_size = gso_size;
shinfo->gso_type = gso_type;
skb_shinfo(skb)->gso_size = gso_size;
skb_shinfo(skb)->gso_type = gso_type;
/* Header must be checked, and gso_segs computed. */
skb_shinfo(skb)->gso_type |= SKB_GSO_DODGY;
skb_shinfo(skb)->gso_segs = 0;
/* Header must be checked, and gso_segs computed. */
shinfo->gso_type |= SKB_GSO_DODGY;
shinfo->gso_segs = 0;
}
}
return 0;