CVE-2024-49948 — net: add more sanity checks to qdisc_pkt_len_init()

Affected: Linux, Siemens RUGGEDCOM RST2428P, Siemens SCALANCE XC-300/XR-300/XC-400/XR-500WG/XR-500 family, Siemens SCALANCE XCM-/XRM-/XCH-/XRH-300 family, Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP, Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

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.

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CVE-2024-49948 — net: add more sanity checks to qdisc_pkt_len_init()