CVE-2025-40254 (GCVE-0-2025-40254)

Vulnerability from cvelistv5 – Published: 2025-12-04 16:08 – Updated: 2025-12-06 21:38
VLAI?
Title
net: openvswitch: remove never-working support for setting nsh fields
Summary
In 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.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 , < 3415faa1fcb4150f29a72c5ecf959339d797feb7 (git)
Affected: b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 , < 3d2e7d3b28469081ccf08301df07cc411a1cc5e9 (git)
Affected: b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 , < f95bef5ba0b88d971b02c776f24bd17544930a3a (git)
Affected: b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 , < 87d2429381ddcf8cbd30c8c36793a4f7916d5f99 (git)
Affected: b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 , < 0b903f33c31c82b1c3591279fd8a23893802b987 (git)
Affected: b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 , < 9c61d8fe1350b7322f4953318165d6719c3b1475 (git)
Affected: b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 , < 4689ba45296dbb3a47e70a1bc2ed0328263e48f3 (git)
Affected: b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3 , < dfe28c4167a9259fc0c372d9f9473e1ac95cff67 (git)
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    Linux Linux Affected: 4.15
Unaffected: 0 , < 4.15 (semver)
Unaffected: 5.4.302 , ≤ 5.4.* (semver)
Unaffected: 5.10.247 , ≤ 5.10.* (semver)
Unaffected: 5.15.197 , ≤ 5.15.* (semver)
Unaffected: 6.1.159 , ≤ 6.1.* (semver)
Unaffected: 6.6.118 , ≤ 6.6.* (semver)
Unaffected: 6.12.60 , ≤ 6.12.* (semver)
Unaffected: 6.17.10 , ≤ 6.17.* (semver)
Unaffected: 6.18 , ≤ * (original_commit_for_fix)
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{
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/openvswitch/actions.c",
            "net/openvswitch/flow_netlink.c",
            "net/openvswitch/flow_netlink.h"
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            "net/openvswitch/flow_netlink.c",
            "net/openvswitch/flow_netlink.h"
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
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              "status": "unaffected",
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              "status": "unaffected",
              "version": "5.10.247",
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              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.197",
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      "cpeApplicability": [
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: openvswitch: remove never-working support for setting nsh fields\n\nThe validation of the set(nsh(...)) action is completely wrong.\nIt runs through the nsh_key_put_from_nlattr() function that is the\nsame function that validates NSH keys for the flow match and the\npush_nsh() action.  However, the set(nsh(...)) has a very different\nmemory layout.  Nested attributes in there are doubled in size in\ncase of the masked set().  That makes proper validation impossible.\n\nThere is also confusion in the code between the \u0027masked\u0027 flag, that\nsays that the nested attributes are doubled in size containing both\nthe value and the mask, and the \u0027is_mask\u0027 that says that the value\nwe\u0027re parsing is the mask.  This is causing kernel crash on trying to\nwrite into mask part of the match with SW_FLOW_KEY_PUT() during\nvalidation, while validate_nsh() doesn\u0027t allocate any memory for it:\n\n  BUG: kernel NULL pointer dereference, address: 0000000000000018\n  #PF: supervisor read access in kernel mode\n  #PF: error_code(0x0000) - not-present page\n  PGD 1c2383067 P4D 1c2383067 PUD 20b703067 PMD 0\n  Oops: Oops: 0000 [#1] SMP NOPTI\n  CPU: 8 UID: 0 Kdump: loaded Not tainted 6.17.0-rc4+ #107 PREEMPT(voluntary)\n  RIP: 0010:nsh_key_put_from_nlattr+0x19d/0x610 [openvswitch]\n  Call Trace:\n   \u003cTASK\u003e\n   validate_nsh+0x60/0x90 [openvswitch]\n   validate_set.constprop.0+0x270/0x3c0 [openvswitch]\n   __ovs_nla_copy_actions+0x477/0x860 [openvswitch]\n   ovs_nla_copy_actions+0x8d/0x100 [openvswitch]\n   ovs_packet_cmd_execute+0x1cc/0x310 [openvswitch]\n   genl_family_rcv_msg_doit+0xdb/0x130\n   genl_family_rcv_msg+0x14b/0x220\n   genl_rcv_msg+0x47/0xa0\n   netlink_rcv_skb+0x53/0x100\n   genl_rcv+0x24/0x40\n   netlink_unicast+0x280/0x3b0\n   netlink_sendmsg+0x1f7/0x430\n   ____sys_sendmsg+0x36b/0x3a0\n   ___sys_sendmsg+0x87/0xd0\n   __sys_sendmsg+0x6d/0xd0\n   do_syscall_64+0x7b/0x2c0\n   entry_SYSCALL_64_after_hwframe+0x76/0x7e\n\nThe third issue with this process is that while trying to convert\nthe non-masked set into masked one, validate_set() copies and doubles\nthe size of the OVS_KEY_ATTR_NSH as if it didn\u0027t have any nested\nattributes.  It should be copying each nested attribute and doubling\nthem in size independently.  And the process must be properly reversed\nduring the conversion back from masked to a non-masked variant during\nthe flow dump.\n\nIn the end, the only two outcomes of trying to use this action are\neither validation failure or a kernel crash.  And if somehow someone\nmanages to install a flow with such an action, it will most definitely\nnot do what it is supposed to, since all the keys and the masks are\nmixed up.\n\nFixing all the issues is a complex task as it requires re-writing\nmost of the validation code.\n\nGiven that and the fact that this functionality never worked since\nintroduction, let\u0027s just remove it altogether.  It\u0027s better to\nre-introduce it later with a proper implementation instead of trying\nto fix it in stable releases."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-12-06T21:38:52.361Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/3415faa1fcb4150f29a72c5ecf959339d797feb7"
        },
        {
          "url": "https://git.kernel.org/stable/c/3d2e7d3b28469081ccf08301df07cc411a1cc5e9"
        },
        {
          "url": "https://git.kernel.org/stable/c/f95bef5ba0b88d971b02c776f24bd17544930a3a"
        },
        {
          "url": "https://git.kernel.org/stable/c/87d2429381ddcf8cbd30c8c36793a4f7916d5f99"
        },
        {
          "url": "https://git.kernel.org/stable/c/0b903f33c31c82b1c3591279fd8a23893802b987"
        },
        {
          "url": "https://git.kernel.org/stable/c/9c61d8fe1350b7322f4953318165d6719c3b1475"
        },
        {
          "url": "https://git.kernel.org/stable/c/4689ba45296dbb3a47e70a1bc2ed0328263e48f3"
        },
        {
          "url": "https://git.kernel.org/stable/c/dfe28c4167a9259fc0c372d9f9473e1ac95cff67"
        }
      ],
      "title": "net: openvswitch: remove never-working support for setting nsh fields",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-40254",
    "datePublished": "2025-12-04T16:08:16.305Z",
    "dateReserved": "2025-04-16T07:20:57.181Z",
    "dateUpdated": "2025-12-06T21:38:52.361Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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