net: gso: fix tcp fraglist segmentation after pull from frag_list

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: net: gso: fix tcp fraglist segmentation after pull from frag_list Detect tcp 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 TCP, this causes a NULL ptr deref in __tcpv4_gso_segment_list_csum at tcp_hdr(seg->next). 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. Approach and description based on a patch by Willem de Bruijn.

References

• https://git.kernel.org/stable/c/75733986fcb0725c0033cde94764389e287b331e
• https://git.kernel.org/stable/c/e19201b0c67da5146eaac06fd3d44bd7945c3448
• https://git.kernel.org/stable/c/3fdd8c83e83fa5e82f1b5585245c51e0355c9f46
• https://git.kernel.org/stable/c/2d4a83a44428de45bfe9dccb0192a3711d1097e0
• https://git.kernel.org/stable/c/17bd3bd82f9f79f3feba15476c2b2c95a9b11ff8