CVE-2024-49948

In the Linux kernel, the following vulnerability has been resolved:

net: add more sanity checks to qdisc_pkt_len_init()

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.