NULL Pointer Dereference Affecting kernel-debug package, versions *

Note: Versions mentioned in the description apply only to the upstream kernel-debug package and not the kernel-debug package as distributed by RHEL. See How to fix? for RHEL:8 relevant fixed versions and status.

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

gso: fix udp gso fraglist segmentation after pull from frag_list

Detect gso fraglist skbs with corrupted geometry (see below) and pass these to skb_segment instead of skb_segment_list, as the first can segment them correctly.

Valid SKB_GSO_FRAGLIST skbs

• consist of two or more segments
• the head_skb holds the protocol headers plus first gso_size
• one or more frag_list skbs hold exactly one segment
• all but the last must be gso_size

Optional datapath hooks such as NAT and BPF (bpf_skb_pull_data) can modify these skbs, breaking these invariants.

In extreme cases they pull all data into skb linear. For UDP, this causes a NULL ptr deref in __udpv4_gso_segment_list_csum at udp_hdr(seg->next)->dest.

Detect invalid geometry due to pull, by checking head_skb size. Don't just drop, as this may blackhole a destination. Convert to be able to pass to regular skb_segment.

• https://access.redhat.com/security/cve/CVE-2024-49978
• https://git.kernel.org/stable/c/080e6c9a3908de193a48f646c5ce1bfb15676ffc
• https://git.kernel.org/stable/c/33e28acf42ee863f332a958bfc2f1a284a3659df
• https://git.kernel.org/stable/c/3cd00d2e3655fad3bda96dc1ebf17b6495f86fea
• https://git.kernel.org/stable/c/a1e40ac5b5e9077fe1f7ae0eb88034db0f9ae1ab
• https://git.kernel.org/stable/c/af3122f5fdc0d00581d6e598a668df6bf54c9daa