{"id":"CVE-2026-74714","summary":"bpf: tcp: Fix use-after-free in bpf_iter_tcp_established_batch()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: tcp: Fix use-after-free in bpf_iter_tcp_established_batch()\n\nreqsk_queue_hash_req() publishes a TCP_NEW_SYN_RECV request_sock onto\nthe ehash chain, drops the bucket lock, and only afterwards sets\nrsk_refcnt to 3.\n\nLockless readers such as __inet_lookup_established() handle this with\nrefcount_inc_not_zero(), but bpf_iter_tcp_established_batch() uses plain\nsock_hold() while holding the bucket lock, on the assumption that the\nlock guarantees sk_refcnt \u003e 0. That assumption does not hold for\nrequest_sock:\n\n  CPU 0                                CPU 1\n  -----                                -----\n  tcp_conn_request()\n   reqsk_queue_hash_req()\n    inet_ehash_insert(req)\n     spin_lock(bucket)\n     __sk_nulls_add_node_rcu(req)      // rsk_refcnt == 0\n     spin_unlock(bucket)\n                                       bpf_iter_tcp_established_batch()\n                                        spin_lock(bucket)\n                                        sock_hold(req)   \u003c-- addition on 0\n                                        spin_unlock(bucket)\n    refcount_set(&req-\u003ersk_refcnt, 3)  // clobbers saturated value\n\nwhich surfaces as:\n\n  refcount_t: addition on 0; use-after-free.\n  WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x48/0x90, CPU#1\n  Call Trace:\n   bpf_iter_tcp_established_batch+0x14e/0x170\n   bpf_iter_tcp_batch+0x53/0x200\n   bpf_iter_tcp_seq_next+0x27/0x70\n   bpf_seq_read+0x107/0x410\n   vfs_read+0xb9/0x380\n\nThe iterator's stolen reference is lost when the publishing CPU's\nrefcount_set() overwrites the count, leaving the socket one reference\nshort. When the last legitimate owner drops its reference the reqsk is\nfreed while still reachable, leading to use-after-free.\n\nThis reproduces in seconds with tcp_syncookies=0, a handful of threads\ndoing connect()/close() to a local listener while others read an\niter/tcp link in a tight loop.\n\nUse refcount_inc_not_zero() and skip the socket on failure. A skipped\nsocket is still part of the bucket, so keep counting it in expected.\nThe reallocations are sized from expected, and a request sock whose\nrefcount gets published while the lock is held across the last realloc\nmust already have room.\n\nA skipped socket is counted in expected but never batched, so end_sk\ncan be short of expected on a batch that is actually complete. Decide\ncompleteness by whether the walk left any socket behind instead. The\nWARN after the locked realloc checks the same, replacing an\nend_sk == expected check that could not hold on that path since\ncommit cdec67a489d4 (\"bpf: tcp: Make sure iter-\u003ebatch always\ncontains a full bucket snapshot\").\n\nIf every matching socket in a bucket is mid-init (refcount 0), end_sk\nstays 0. Advance to the next bucket rather than returning a batch entry\nthat was never filled this round.","modified":"2026-08-27T11:30:51.917407574Z","published":"2026-08-22T15:33:09.643Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74714.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/7d2b60a4bc0499f62ff8520af6309bbe170882fd"},{"type":"WEB","url":"https://git.kernel.org/stable/c/97e74d3e45d653c07c2d406fc530a9bbe3df8396"},{"type":"WEB","url":"https://git.kernel.org/stable/c/cc0295f89296ed351fc4b0b48fee887ba02c5d24"},{"type":"WEB","url":"https://git.kernel.org/stable/c/cefcbbe20846a45f9a7dae868f7ef1000953e2df"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ddbe966b5d1fe212ada749bc3d0b410f1a7dea74"},{"type":"WEB","url":"https://git.kernel.org/stable/c/e5fd3f514e27db1f05fbd72ba615d74941e23c51"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74714.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-74714"},{"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":"04c7820b776f1c4b48698574c47de9e940d368e8"},{"fixed":"cc0295f89296ed351fc4b0b48fee887ba02c5d24"},{"fixed":"ddbe966b5d1fe212ada749bc3d0b410f1a7dea74"},{"fixed":"7d2b60a4bc0499f62ff8520af6309bbe170882fd"},{"fixed":"cefcbbe20846a45f9a7dae868f7ef1000953e2df"},{"fixed":"97e74d3e45d653c07c2d406fc530a9bbe3df8396"},{"fixed":"e5fd3f514e27db1f05fbd72ba615d74941e23c51"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-74714.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.15.0"},{"fixed":"6.1.183"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.152"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.104"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.45"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.1.9"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-74714.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}