{"id":"CVE-2026-98541","summary":"fou: reject omitted FOU_ATTR_IPPROTO on FOU_ENCAP_DIRECT","details":"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't 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).","modified":"2026-10-20T02:31:07.060666236Z","published":"2026-10-18T15:18:09.190Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98541.json"},"references":[{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"},{"type":"WEB","url":"https://git.kernel.org/stable/c/3bcc1624cc1cdcc05b566475d6e848093ab2a8f6"},{"type":"WEB","url":"https://git.kernel.org/stable/c/46b1ffb7e169c7e401dd890b29e55dbc261f8f01"},{"type":"WEB","url":"https://git.kernel.org/stable/c/520cf06b8ea0ba5bcc1b8b982ef07f02b5e56221"},{"type":"WEB","url":"https://git.kernel.org/stable/c/7f4ba56f5d310dd018972916167985010a5d66a1"},{"type":"WEB","url":"https://git.kernel.org/stable/c/8b43f40798bb2758489fbbcae7e841ad4443c213"},{"type":"WEB","url":"https://git.kernel.org/stable/c/b1229b210ef5a39c58be665e6798203751411842"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d22609f3d13fc5baacd92c222731b03c593401db"},{"type":"WEB","url":"https://git.kernel.org/stable/c/fd20220f86947d66d4dba2d76f13a28dbd86ef30"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98541.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98541"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"23461551c00628c3f3fe9cf837bf53cf8f212b63"},{"fixed":"fd20220f86947d66d4dba2d76f13a28dbd86ef30"},{"fixed":"46b1ffb7e169c7e401dd890b29e55dbc261f8f01"},{"fixed":"7f4ba56f5d310dd018972916167985010a5d66a1"},{"fixed":"3bcc1624cc1cdcc05b566475d6e848093ab2a8f6"},{"fixed":"8b43f40798bb2758489fbbcae7e841ad4443c213"},{"fixed":"b1229b210ef5a39c58be665e6798203751411842"},{"fixed":"520cf06b8ea0ba5bcc1b8b982ef07f02b5e56221"},{"fixed":"d22609f3d13fc5baacd92c222731b03c593401db"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98541.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"3.18.0"},{"fixed":"5.10.271"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.222"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.189"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.158"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.112"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.55"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.2.9"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98541.json"}}],"schema_version":"1.9.0"}