bpf: tcp: Fix use-after-free in bpf_iter_tcp_established_batch()

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-74714
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-22 16:16:46 UTC
Updated2026-08-22 16:16:46 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: bpf: tcp: Fix use-after-free in bpf_iter_tcp_established_batch() reqsk_queue_hash_req() publishes a TCP_NEW_SYN_RECV request_sock onto the ehash chain, drops the bucket lock, and only afterwards sets rsk_refcnt to 3. Lockless readers such as __inet_lookup_established() handle this with refcount_inc_not_zero(), but bpf_iter_tcp_established_batch() uses plain sock_hold() while holding the bucket lock, on the assumption that the lock guarantees sk_refcnt > 0. That assumption does not hold for request_sock: CPU 0 CPU 1 ----- ----- tcp_conn_request() reqsk_queue_hash_req() inet_ehash_insert(req) spin_lock(bucket) __sk_nulls_add_node_rcu(req) // rsk_refcnt == 0 spin_unlock(bucket) bpf_iter_tcp_established_batch() spin_lock(bucket) sock_hold(req) <-- addition on 0 spin_unlock(bucket) refcount_set(&req->rsk_refcnt, 3) // clobbers saturated value which surfaces as: refcount_t: addition on 0; use-after-free. WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x48/0x90, CPU#1 Call Trace: bpf_iter_tcp_established_batch+0x14e/0x170 bpf_iter_tcp_batch+0x53/0x200 bpf_iter_tcp_seq_next+0x27/0x70 bpf_seq_read+0x107/0x410 vfs_read+0xb9/0x380 The iterator's stolen reference is lost when the publishing CPU's refcount_set() overwrites the count, leaving the socket one reference short. When the last legitimate owner drops its reference the reqsk is freed while still reachable, leading to use-after-free. This reproduces in seconds with tcp_syncookies=0, a handful of threads doing connect()/close() to a local listener while others read an iter/tcp link in a tight loop. Use refcount_inc_not_zero() and skip the socket on failure. A skipped socket is still part of the bucket, so keep counting it in expected. The reallocations are sized from expected, and a request sock whose refcount gets published while the lock is held across the last realloc must already have room. A skipped socket is counted in expected but never batched, so end_sk can be short of expected on a batch that is actually complete. Decide completeness by whether the walk left any socket behind instead. The WARN after the locked realloc checks the same, replacing an end_sk == expected check that could not hold on that path since commit cdec67a489d4 ("bpf: tcp: Make sure iter->batch always contains a full bucket snapshot"). If every matching socket in a bucket is mid-init (refcount 0), end_sk stays 0. Advance to the next bucket rather than returning a batch entry that was never filled this round.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 04c7820b776f1c4b48698574c47de9e940d368e8 cc0295f89296ed351fc4b0b48fee887ba02c5d24 git Not specified
CNA Linux Linux affected 04c7820b776f1c4b48698574c47de9e940d368e8 ddbe966b5d1fe212ada749bc3d0b410f1a7dea74 git Not specified
CNA Linux Linux affected 04c7820b776f1c4b48698574c47de9e940d368e8 7d2b60a4bc0499f62ff8520af6309bbe170882fd git Not specified
CNA Linux Linux affected 04c7820b776f1c4b48698574c47de9e940d368e8 cefcbbe20846a45f9a7dae868f7ef1000953e2df git Not specified
CNA Linux Linux affected 04c7820b776f1c4b48698574c47de9e940d368e8 97e74d3e45d653c07c2d406fc530a9bbe3df8396 git Not specified
CNA Linux Linux affected 04c7820b776f1c4b48698574c47de9e940d368e8 e5fd3f514e27db1f05fbd72ba615d74941e23c51 git Not specified
CNA Linux Linux affected 5.15 Not specified
CNA Linux Linux unaffected 5.15 semver Not specified
CNA Linux Linux unaffected 6.1.183 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.152 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.104 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.45 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.9 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/97e74d3e45d653c07c2d406fc530a9bbe3df8396 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/cc0295f89296ed351fc4b0b48fee887ba02c5d24 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/cefcbbe20846a45f9a7dae868f7ef1000953e2df 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/e5fd3f514e27db1f05fbd72ba615d74941e23c51 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/7d2b60a4bc0499f62ff8520af6309bbe170882fd 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ddbe966b5d1fe212ada749bc3d0b410f1a7dea74 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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