Subject: CVE-2024-49978: gso: fix udp gso fraglist segmentation after pull from frag_list

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2024-49978 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.6 with commit 9fd1ff5d2ac7 and fixed in 6.1.113 with commit 080e6c9a3908
	Issue introduced in 5.6 with commit 9fd1ff5d2ac7 and fixed in 6.6.55 with commit af3122f5fdc0
	Issue introduced in 5.6 with commit 9fd1ff5d2ac7 and fixed in 6.10.14 with commit 33e28acf42ee
	Issue introduced in 5.6 with commit 9fd1ff5d2ac7 and fixed in 6.11.3 with commit 3cd00d2e3655
	Issue introduced in 5.6 with commit 9fd1ff5d2ac7 and fixed in 6.12-rc2 with commit a1e40ac5b5e9

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-49978
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	net/ipv4/udp_offload.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/080e6c9a3908de193a48f646c5ce1bfb15676ffc
	https://git.kernel.org/stable/c/af3122f5fdc0d00581d6e598a668df6bf54c9daa
	https://git.kernel.org/stable/c/33e28acf42ee863f332a958bfc2f1a284a3659df
	https://git.kernel.org/stable/c/3cd00d2e3655fad3bda96dc1ebf17b6495f86fea
	https://git.kernel.org/stable/c/a1e40ac5b5e9077fe1f7ae0eb88034db0f9ae1ab