CVE-2024-49949

/// Technical description

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

net: avoid potential underflow in qdisc_pkt_len_init() with UFO

After commit 7c6d2ecbda83 ("net: be more gentle about silly gso

requests coming from user") virtio_net_hdr_to_skb() had sanity check

to detect malicious attempts from user space to cook a bad GSO packet.

Then commit cf9acc90c80ec ("net: virtio_net_hdr_to_skb: count

transport header in UFO") while fixing one issue, allowed user space

to cook a GSO packet with the following characteristic :

IPv4 SKB_GSO_UDP, gso_size=3, skb->len = 28.

When this packet arrives in qdisc_pkt_len_init(), we end up

with hdr_len = 28 (IPv4 header + UDP header), matching skb->len

Then the following sets gso_segs to 0 :

gso_segs = DIV_ROUND_UP(skb->len - hdr_len,

shinfo->gso_size);

Then later we set qdisc_skb_cb(skb)->pkt_len to back to zero :/

qdisc_skb_cb(skb)->pkt_len += (gso_segs - 1) * hdr_len;

This leads to the following crash in fq_codel [1]

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References