CVE-2026-74371: bpf: fix BPF_PROG_QUERY OOB write and cgroup backward compat

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

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

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

bpf: fix BPF_PROG_QUERY OOB write and cgroup backward compat

BPF_PROG_QUERY writes back the 'query.revision' field unconditionally to
userspace. If userspace passes a smaller 'bpf_attr' structure (e.g. 40
bytes, which was the layout before the addition of 'query.revision'),
the kernel performs an out-of-bounds write.

Fix this by propagating the user-provided attribute size 'uattr_size'
down to the cgroup query handlers, and conditionally skipping writing
the revision field to userspace when the provided buffer size is
insufficient.

query.revision in bpf_mprog_query is structurally identical to the
cgroup case: a late tail field, written unconditionally.

But the backward-compat hazard is not the same.

The min-historical-size test is per command, and bpf_mprog_query only
serves attach types that were born with revision in the struct:

- tcx_prog_query -> BPF_TCX_INGRESS/EGRESS
- netkit_prog_query -> BPF_NETKIT_PRIMARY/PEER

tcx, netkit, the revision field, and bpf_mprog_query itself all landed in
the same v6.6 merge window (053c8e1f235d added the mprog query API +
revision; tcx in e420bed02507, netkit in 35dfaad7188c). There has never
been a tcx/netkit BPF_PROG_QUERY userspace that doesn't know about
revision. So for these commands the minimum legitimate struct already
covers offset 56-64 — no old binary can be broken here.

Contrast with cgroup: BPF_PROG_QUERY on cgroup attach types shipped in
2017; revision write-back was bolted on years later (120933984460). That
path has a real population of pre-revision callers.

The Linux kernel CVE team has assigned CVE-2026-74371 to this issue.


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

	Issue introduced in 6.17 with commit 1209339844601ec1766f4ff430673fbcfe42bb51 and fixed in 6.18.40 with commit a7131340d0f95df9a541257dccab5d85e6bcdd2b
	Issue introduced in 6.17 with commit 1209339844601ec1766f4ff430673fbcfe42bb51 and fixed in 7.1.5 with commit d3d630e8a7f3421bc2d204b87bdff35b4432a8e3
	Issue introduced in 6.17 with commit 1209339844601ec1766f4ff430673fbcfe42bb51 and fixed in 7.2-rc1 with commit 21c4b99b27f3f85b89256e81b3e997dec0a460d0

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-2026-74371
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:
	include/linux/bpf-cgroup.h
	kernel/bpf/cgroup.c
	kernel/bpf/syscall.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/a7131340d0f95df9a541257dccab5d85e6bcdd2b
	https://git.kernel.org/stable/c/d3d630e8a7f3421bc2d204b87bdff35b4432a8e3
	https://git.kernel.org/stable/c/21c4b99b27f3f85b89256e81b3e997dec0a460d0