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net: validate untrusted gso packets without csum offload

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Syzkaller again found a path to a kernel crash through bad gso input.
By building an excessively large packet to cause an skb field to wrap.

If VIRTIO_NET_HDR_F_NEEDS_CSUM was set this would have been dropped in
skb_partial_csum_set.

GSO packets that do not set checksum offload are suspicious and rare.
Most callers of virtio_net_hdr_to_skb already pass them to
skb_probe_transport_header.

Move that test forward, change it to detect parse failure and drop
packets on failure as those cleary are not one of the legitimate
VIRTIO_NET_HDR_GSO types.

Fixes: bfd5f4a3d6 ("packet: Add GSO/csum offload support.")
Fixes: f43798c276 ("tun: Allow GSO using virtio_net_hdr")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Willem de Bruijn 2019-02-15 12:15:47 -05:00 committed by David S. Miller
parent 3b89ea9c59
commit d5be7f632b
2 changed files with 10 additions and 1 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

2
include/linux/skbuff.h
View file

@ -2434,7 +2434,7 @@ static inline void skb_probe_transport_header(struct sk_buff *skb,
if (skb_flow_dissect_flow_keys_basic(skb, &keys, NULL, 0, 0, 0, 0))
skb_set_transport_header(skb, keys.control.thoff);
else
else if (offset_hint >= 0)
skb_set_transport_header(skb, offset_hint);
}

9
include/linux/virtio_net.h
View file

@ -57,6 +57,15 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
if (!skb_partial_csum_set(skb, start, off))
return -EINVAL;
} else {
/* gso packets without NEEDS_CSUM do not set transport_offset.
* probe and drop if does not match one of the above types.
*/
if (gso_type) {
skb_probe_transport_header(skb, -1);
if (!skb_transport_header_was_set(skb))
return -EINVAL;
}
}
if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {