{"id":"CVE-2026-64459","summary":"tcp: restore RCU grace period in tcp_ao_destroy_sock","details":"In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: restore RCU grace period in tcp_ao_destroy_sock\n\nCommit 51e547e8c89c (\"tcp: Free TCP-AO/TCP-MD5 info/keys without RCU\")\nremoved the call_rcu() callback from tcp_ao_destroy_sock(), arguing that\n\"the destruction of info/keys is delayed until the socket destructor\"\nand therefore \"no one can discover it anymore\".\n\nThat argument does not hold for the call site in tcp_connect()\n(net/ipv4/tcp_output.c:4327-4332). At that point the socket is in\nTCP_SYN_SENT, has already been inserted into the inet ehash by\ninet_hash_connect() in tcp_v4_connect(), and is therefore very much\ndiscoverable: any softirq running tcp_v4_rcv() on another CPU can take\nthe socket out of the ehash, walk into tcp_inbound_hash(), and load\ntp-\u003eao_info via implicit RCU before bh_lock_sock_nested() is taken on\nthe destroying CPU.\n\nThe reader path then enters __tcp_ao_do_lookup() (net/ipv4/tcp_ao.c:208)\nwhich re-loads tp-\u003eao_info via rcu_dereference_check(); the re-load can\nstill observe the (about-to-be-freed) pointer because there is no\nsynchronize_rcu() between rcu_assign_pointer(tp-\u003eao_info, NULL) and\ntcp_ao_info_free() in tcp_ao_destroy_sock(). The captured pointer is\nthen walked at line 223:\n\n\thlist_for_each_entry_rcu(key, &ao-\u003ehead, node, ...)\n\nThe writer's synchronous kfree() is free to complete between the line\n218 re-fetch and the line 223 hlist iteration. The slab is reused\n(or simply LIST_POISON1-stamped if not yet reused) and the iteration\nwalks attacker-controlled or poison memory in softirq context.\n\nReproducer (no debug shim, stock x86_64 v7.1-rc2 SMP+KASAN, QEMU+KVM):\nan unprivileged uid=1000 process inside CLONE_NEWUSER|CLONE_NEWNET\ninstalls TCP_MD5SIG + TCP_AO_ADD_KEY on a TCP socket, sprays forged\nTCP-AO segments toward its eventual 4-tuple via raw sockets, then\ncalls connect(). The md5-wins reconciliation in tcp_connect() fires\ntcp_ao_destroy_sock(); the softirq backlog reader on the loopback\nNAPI path crashes on the freed ao-\u003ehead.first walk:\n\n  Oops: general protection fault, probably for non-canonical\n    address 0xfbd59c000000002f\n  KASAN: maybe wild-memory-access in range\n    [0xdead000000000178-0xdead00000000017f]\n  CPU: 0 UID: 1000 PID: 100 Comm: repro_userns\n  RIP: 0010:__tcp_ao_do_lookup+0x107/0x1c0\n  Call Trace: \u003cIRQ\u003e\n    __tcp_ao_do_lookup+0x107/0x1c0\n    tcp_ao_inbound_lookup.constprop.0+0x12a/0x200\n    tcp_inbound_ao_hash+0x5ea/0x1520\n    tcp_inbound_hash+0x7ce/0x1240\n    tcp_v4_rcv+0x1e7a/0x3e10\n    ...\n\nRestore the RCU grace period: re-add struct rcu_head to tcp_ao_info\nand replace the synchronous tcp_ao_info_free() with a call_rcu()\ncallback. Readers that captured tp-\u003eao_info before rcu_assign_pointer\nNULLed it now see the object remain valid until rcu_read_unlock().\nWith the patch applied the reproducer runs cleanly for 2000 iterations\non the same kernel build.","modified":"2026-07-28T04:02:54.360302734Z","published":"2026-07-25T08:51:26.879Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64459.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/4caf12c778fed3dc3824cf36263be5e2c491fbd0"},{"type":"WEB","url":"https://git.kernel.org/stable/c/657646c08c94ef7b9dbe468fe7828032216f9841"},{"type":"WEB","url":"https://git.kernel.org/stable/c/8bc4d43bccbd60efe85d0a44d5bf41762f2f0c30"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64459.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-64459"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"51e547e8c89c661f6fbede4a28b1d33b13625683"},{"fixed":"657646c08c94ef7b9dbe468fe7828032216f9841"},{"fixed":"4caf12c778fed3dc3824cf36263be5e2c491fbd0"},{"fixed":"8bc4d43bccbd60efe85d0a44d5bf41762f2f0c30"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64459.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.18.0"},{"fixed":"6.18.39"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.1.4"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64459.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"}]}