net: openvswitch: remove never-working support for setting nsh fields

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Summary

CVECVE-2025-40254
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-12-04 16:16:19 UTC
Updated2026-06-02 14:16:32 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: net: openvswitch: remove never-working support for setting nsh fields The validation of the set(nsh(...)) action is completely wrong. It runs through the nsh_key_put_from_nlattr() function that is the same function that validates NSH keys for the flow match and the push_nsh() action. However, the set(nsh(...)) has a very different memory layout. Nested attributes in there are doubled in size in case of the masked set(). That makes proper validation impossible. There is also confusion in the code between the 'masked' flag, that says that the nested attributes are doubled in size containing both the value and the mask, and the 'is_mask' that says that the value we're parsing is the mask. This is causing kernel crash on trying to write into mask part of the match with SW_FLOW_KEY_PUT() during validation, while validate_nsh() doesn't allocate any memory for it: BUG: kernel NULL pointer dereference, address: 0000000000000018 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 1c2383067 P4D 1c2383067 PUD 20b703067 PMD 0 Oops: Oops: 0000 [#1] SMP NOPTI CPU: 8 UID: 0 Kdump: loaded Not tainted 6.17.0-rc4+ #107 PREEMPT(voluntary) RIP: 0010:nsh_key_put_from_nlattr+0x19d/0x610 [openvswitch] Call Trace: <TASK> validate_nsh+0x60/0x90 [openvswitch] validate_set.constprop.0+0x270/0x3c0 [openvswitch] __ovs_nla_copy_actions+0x477/0x860 [openvswitch] ovs_nla_copy_actions+0x8d/0x100 [openvswitch] ovs_packet_cmd_execute+0x1cc/0x310 [openvswitch] genl_family_rcv_msg_doit+0xdb/0x130 genl_family_rcv_msg+0x14b/0x220 genl_rcv_msg+0x47/0xa0 netlink_rcv_skb+0x53/0x100 genl_rcv+0x24/0x40 netlink_unicast+0x280/0x3b0 netlink_sendmsg+0x1f7/0x430 ____sys_sendmsg+0x36b/0x3a0 ___sys_sendmsg+0x87/0xd0 __sys_sendmsg+0x6d/0xd0 do_syscall_64+0x7b/0x2c0 entry_SYSCALL_64_after_hwframe+0x76/0x7e The third issue with this process is that while trying to convert the non-masked set into masked one, validate_set() copies and doubles the size of the OVS_KEY_ATTR_NSH as if it didn't have any nested attributes. It should be copying each nested attribute and doubling them in size independently. And the process must be properly reversed during the conversion back from masked to a non-masked variant during the flow dump. In the end, the only two outcomes of trying to use this action are either validation failure or a kernel crash. And if somehow someone manages to install a flow with such an action, it will most definitely not do what it is supposed to, since all the keys and the masks are mixed up. Fixing all the issues is a complex task as it requires re-writing most of the validation code. Given that and the fact that this functionality never worked since introduction, let's just remove it altogether. It's better to re-introduce it later with a proper implementation instead of trying to fix it in stable releases.

Risk And Classification

EPSS: 0.000670000 probability, percentile 0.207630000 (date 2026-06-02)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 3415faa1fcb4150f29a72c5ecf959339d797feb7 git Not specified
CNA Linux Linux affected b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 3d2e7d3b28469081ccf08301df07cc411a1cc5e9 git Not specified
CNA Linux Linux affected b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 f95bef5ba0b88d971b02c776f24bd17544930a3a git Not specified
CNA Linux Linux affected b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 87d2429381ddcf8cbd30c8c36793a4f7916d5f99 git Not specified
CNA Linux Linux affected b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 0b903f33c31c82b1c3591279fd8a23893802b987 git Not specified
CNA Linux Linux affected b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 9c61d8fe1350b7322f4953318165d6719c3b1475 git Not specified
CNA Linux Linux affected b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 4689ba45296dbb3a47e70a1bc2ed0328263e48f3 git Not specified
CNA Linux Linux affected b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 dfe28c4167a9259fc0c372d9f9473e1ac95cff67 git Not specified
CNA Linux Linux affected 4.15 Not specified
CNA Linux Linux unaffected 4.15 semver Not specified
CNA Linux Linux unaffected 5.4.302 5.4.* semver Not specified
CNA Linux Linux unaffected 5.10.247 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.197 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.159 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.118 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.60 6.12.* semver Not specified
CNA Linux Linux unaffected 6.17.10 6.17.* semver Not specified
CNA Linux Linux unaffected 6.18 * original_commit_for_fix Not specified
ADP Siemens RUGGEDCOM RST2428P affected V4.0 custom Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/dfe28c4167a9259fc0c372d9f9473e1ac95cff67 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/9c61d8fe1350b7322f4953318165d6719c3b1475 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/3415faa1fcb4150f29a72c5ecf959339d797feb7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/4689ba45296dbb3a47e70a1bc2ed0328263e48f3 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
cert-portal.siemens.com/productcert/html/ssa-253495.html 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e cert-portal.siemens.com
git.kernel.org/stable/c/3d2e7d3b28469081ccf08301df07cc411a1cc5e9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f95bef5ba0b88d971b02c776f24bd17544930a3a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/0b903f33c31c82b1c3591279fd8a23893802b987 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/87d2429381ddcf8cbd30c8c36793a4f7916d5f99 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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