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net: add more sanity checks to qdisc_pkt_len_init()

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One path takes care of SKB_GSO_DODGY, assuming
skb->len is bigger than hdr_len.

virtio_net_hdr_to_skb() does not fully dissect TCP headers,
it only make sure it is at least 20 bytes.

It is possible for an user to provide a malicious 'GSO' packet,
total length of 80 bytes.

- 20 bytes of IPv4 header
- 60 bytes TCP header
- a small gso_size like 8

virtio_net_hdr_to_skb() would declare this packet as a normal
GSO packet, because it would see 40 bytes of payload,
bigger than gso_size.

We need to make detect this case to not underflow
qdisc_skb_cb(skb)->pkt_len.

Fixes: 1def9238d4 ("net_sched: more precise pkt_len computation")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Eric Dumazet 2024-09-24 15:02:57 +00:00 committed by Paolo Abeni
parent c20029db28
commit ab9a9a9e96
1 changed files with 7 additions and 3 deletions
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10
net/core/dev.c
View file

@ -3766,10 +3766,14 @@ static void qdisc_pkt_len_init(struct sk_buff *skb)
hdr_len += sizeof(struct udphdr);
}
if (shinfo->gso_type & SKB_GSO_DODGY)
gso_segs = DIV_ROUND_UP(skb->len - hdr_len,
shinfo->gso_size);
if (unlikely(shinfo->gso_type & SKB_GSO_DODGY)) {
int payload = skb->len - hdr_len;
/* Malicious packet. */
if (payload <= 0)
return;
gso_segs = DIV_ROUND_UP(payload, shinfo->gso_size);
}
qdisc_skb_cb(skb)->pkt_len += (gso_segs - 1) * hdr_len;
}
}