CVE-2026-64531: net: openvswitch: reject oversized nested action attrs

CVE-2026-64531: net: openvswitch: reject oversized nested action attrs

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

net: openvswitch: reject oversized nested action attrs

Open vSwitch stores generated flow actions as nlattrs, whose nla_len
field is u16. Commit a1e64addf3ff ("net: openvswitch: remove
misbehaving actions length check") allowed the total sw_flow_actions
stream to grow beyond 64 KiB, which is valid, but also removed the last
guard preventing a generated nested action attribute from exceeding
U16_MAX.

An oversized generated container can thus be closed with a truncated
nla_len. A later dump or teardown then walks a structurally different
stream than the one that was validated. In particular, an oversized
nested CLONE/CT action may cause subsequent bytes in the generated
stream to be interpreted as independent actions.

Keep the larger total-action-stream behavior, but make nested action
close reject generated containers that do not fit in nla_len, and return
the error through all callers. For recursive SAMPLE, CLONE, DEC_TTL, and
CHECK_PKT_LEN builders, trim resource-owning action-list tails in reverse
construction order before discarding failed wrappers, so resources copied
into the rejected tails are released before the wrappers are removed.

Most failed outer wrappers are discarded by truncating actions_len after
child resources have been released. CHECK_PKT_LEN also trims its parent
after branch resources are gone. SET/TUNNEL close failures unwind their
known tun_dst ownership directly, and SET_TO_MASKED has no external
ownership and truncates on close failure.

The Linux kernel CVE team has assigned CVE-2026-64531 to this issue.


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

	Issue introduced in 5.15.180 with commit 057dbc5b72e9fcac439cd561c3a539b8a0edeb92 and fixed in 5.15.212 with commit ab855641241387db062a5e41d9ad6b8561542572
	Issue introduced in 6.1.132 with commit 2532adbfe917c0e71dba2650ffc6efe396314c87 and fixed in 6.1.178 with commit c66bd2626c2764f23764ff0f8277f44a9cfe8349
	Issue introduced in 6.6.84 with commit 4b1a0ee6164c7204c68ab5a9c48c07bfe8852485 and fixed in 6.6.145 with commit d573250d228401f707f4dbc09d11227a6215ee5f
	Issue introduced in 6.12.20 with commit e6610f9c08b4c04cf7949c10fc246c071d00e935 and fixed in 6.12.97 with commit f1efff8858403191361a01269c6fe8dd7f55a385
	Issue introduced in 6.14 with commit a1e64addf3ff9257b45b78bc7d743781c3f41340 and fixed in 6.18.40 with commit dbd14f736be02cfe73049bd801af89becd1a0749
	Issue introduced in 6.14 with commit a1e64addf3ff9257b45b78bc7d743781c3f41340 and fixed in 7.1.5 with commit 1b41cbe05b184f8861712f0806cc0c4f5d8c6dfe
	Issue introduced in 6.14 with commit a1e64addf3ff9257b45b78bc7d743781c3f41340 and fixed in 7.2-rc4 with commit 3f1f755366687d051174739fb99f7d560202f60b
	Issue introduced in 6.13.8 with commit 6b099d285d7ed324494b6d684f377aa103856118

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-2026-64531
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/openvswitch/flow_netlink.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/ab855641241387db062a5e41d9ad6b8561542572
	https://git.kernel.org/stable/c/c66bd2626c2764f23764ff0f8277f44a9cfe8349
	https://git.kernel.org/stable/c/d573250d228401f707f4dbc09d11227a6215ee5f
	https://git.kernel.org/stable/c/f1efff8858403191361a01269c6fe8dd7f55a385
	https://git.kernel.org/stable/c/dbd14f736be02cfe73049bd801af89becd1a0749
	https://git.kernel.org/stable/c/1b41cbe05b184f8861712f0806cc0c4f5d8c6dfe
	https://git.kernel.org/stable/c/3f1f755366687d051174739fb99f7d560202f60b