CVE-2026-98541 (GCVE-0-2026-98541)
Vulnerability from cvelistv5
Published
2026-10-18 15:18
Modified
2026-10-19 09:21
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: fou: reject omitted FOU_ATTR_IPPROTO on FOU_ENCAP_DIRECT Commit 7a9bc9e3f423 ("fou: Don't allow 0 for FOU_ATTR_IPPROTO.") added NLA_POLICY_MIN(NLA_U8, 1) to fou_nl_policy[FOU_ATTR_IPPROTO], which rejects an explicitly supplied FOU_ATTR_IPPROTO == 0 attribute with -ERANGE. However, FOU_ATTR_IPPROTO is an optional netlink attribute. When a user sends FOU_CMD_ADD with FOU_ATTR_TYPE set to FOU_ENCAP_DIRECT and omits FOU_ATTR_IPPROTO entirely, nla_policy validation succeeds and parse_nl_config() leaves cfg->protocol as 0 (from memset(cfg, 0, sizeof(*cfg))). fou_create() then creates a FOU_ENCAP_DIRECT socket with fou->protocol == 0. In fou_udp_recv(), returning -fou->protocol to udp_queue_rcv_one_skb() triggers IP protocol resubmission when fou->protocol > 0, whereas returning 0 tells the UDP tunnel layer that the skb was consumed without freeing it. When fou->protocol == 0, every packet received on the socket returns 0 from fou_udp_recv() and leaks the sk_buff. Reject FOU_ENCAP_DIRECT when !cfg->protocol in fou_create() so that creating a direct encapsulation port without FOU_ATTR_IPPROTO fails with -EINVAL while leaving FOU_CMD_DEL and FOU_CMD_GET (which share parse_nl_config()) unaffected. Tested in QEMU against Linux 7.3.0-rc3 by sending a FOU_CMD_ADD Generic Netlink request with FOU_ATTR_PORT = 5555 and FOU_ATTR_TYPE = FOU_ENCAP_DIRECT while omitting FOU_ATTR_IPPROTO. On the unfixed kernel, FOU_CMD_ADD succeeds (err = 0), FOU_CMD_GET reports fou->type = 1 and fou->protocol = 0, and sending 4000 UDP packets to 127.0.0.1:5555 leaks all 4000 sk_buffs (SUnreclaim in /proc/meminfo grows from 41456 kB to 59008 kB, +17552 kB); with this patch applied, FOU_CMD_ADD is rejected with -EINVAL (-22).
References
Impacted products
Vendor Product Version
Linux Linux Version: 23461551c00628c3f3fe9cf837bf53cf8f212b63
Version: 23461551c00628c3f3fe9cf837bf53cf8f212b63
Version: 23461551c00628c3f3fe9cf837bf53cf8f212b63
Version: 23461551c00628c3f3fe9cf837bf53cf8f212b63
Version: 23461551c00628c3f3fe9cf837bf53cf8f212b63
Version: 23461551c00628c3f3fe9cf837bf53cf8f212b63
Version: 23461551c00628c3f3fe9cf837bf53cf8f212b63
Version: 23461551c00628c3f3fe9cf837bf53cf8f212b63
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{
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          "programFiles": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfou: reject omitted FOU_ATTR_IPPROTO on FOU_ENCAP_DIRECT\n\nCommit 7a9bc9e3f423 (\"fou: Don\u0027t allow 0 for FOU_ATTR_IPPROTO.\") added\nNLA_POLICY_MIN(NLA_U8, 1) to fou_nl_policy[FOU_ATTR_IPPROTO], which\nrejects an explicitly supplied FOU_ATTR_IPPROTO == 0 attribute with\n-ERANGE.\n\nHowever, FOU_ATTR_IPPROTO is an optional netlink attribute. When a user\nsends FOU_CMD_ADD with FOU_ATTR_TYPE set to FOU_ENCAP_DIRECT and omits\nFOU_ATTR_IPPROTO entirely, nla_policy validation succeeds and\nparse_nl_config() leaves cfg-\u003eprotocol as 0 (from memset(cfg, 0,\nsizeof(*cfg))). fou_create() then creates a FOU_ENCAP_DIRECT socket with\nfou-\u003eprotocol == 0.\n\nIn fou_udp_recv(), returning -fou-\u003eprotocol to udp_queue_rcv_one_skb()\ntriggers IP protocol resubmission when fou-\u003eprotocol \u003e 0, whereas\nreturning 0 tells the UDP tunnel layer that the skb was consumed without\nfreeing it. When fou-\u003eprotocol == 0, every packet received on the socket\nreturns 0 from fou_udp_recv() and leaks the sk_buff.\n\nReject FOU_ENCAP_DIRECT when !cfg-\u003eprotocol in fou_create() so that\ncreating a direct encapsulation port without FOU_ATTR_IPPROTO fails with\n-EINVAL while leaving FOU_CMD_DEL and FOU_CMD_GET (which share\nparse_nl_config()) unaffected.\n\nTested in QEMU against Linux 7.3.0-rc3 by sending a FOU_CMD_ADD Generic\nNetlink request with FOU_ATTR_PORT = 5555 and FOU_ATTR_TYPE =\nFOU_ENCAP_DIRECT while omitting FOU_ATTR_IPPROTO. On the unfixed kernel,\nFOU_CMD_ADD succeeds (err = 0), FOU_CMD_GET reports fou-\u003etype = 1 and\nfou-\u003eprotocol = 0, and sending 4000 UDP packets to 127.0.0.1:5555 leaks\nall 4000 sk_buffs (SUnreclaim in /proc/meminfo grows from 41456 kB to\n59008 kB, +17552 kB); with this patch applied, FOU_CMD_ADD is rejected\nwith -EINVAL (-22)."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:21:24.620Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/fd20220f86947d66d4dba2d76f13a28dbd86ef30"
        },
        {
          "url": "https://git.kernel.org/stable/c/46b1ffb7e169c7e401dd890b29e55dbc261f8f01"
        },
        {
          "url": "https://git.kernel.org/stable/c/7f4ba56f5d310dd018972916167985010a5d66a1"
        },
        {
          "url": "https://git.kernel.org/stable/c/3bcc1624cc1cdcc05b566475d6e848093ab2a8f6"
        },
        {
          "url": "https://git.kernel.org/stable/c/8b43f40798bb2758489fbbcae7e841ad4443c213"
        },
        {
          "url": "https://git.kernel.org/stable/c/b1229b210ef5a39c58be665e6798203751411842"
        },
        {
          "url": "https://git.kernel.org/stable/c/520cf06b8ea0ba5bcc1b8b982ef07f02b5e56221"
        },
        {
          "url": "https://git.kernel.org/stable/c/d22609f3d13fc5baacd92c222731b03c593401db"
        }
      ],
      "title": "fou: reject omitted FOU_ATTR_IPPROTO on FOU_ENCAP_DIRECT",
      "x_generator": {
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98541",
    "datePublished": "2026-10-18T15:18:09.190Z",
    "dateReserved": "2026-09-25T10:25:14.356Z",
    "dateUpdated": "2026-10-19T09:21:24.620Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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