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([58.123.110.97]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-369e8ec50bcsm37925013eec.23.2026.10.25.17.38.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 25 Oct 2026 17:38:40 -0700 (PDT) From: Hyunwoo Kim To: edumazet@kernel.org, ncardwell@google.com, kuniyu@google.com, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org Cc: Hyunwoo Kim , martin.lau@linux.dev, john.fastabend@gmail.com, weiwan@google.com, sd@queasysnail.net, jiayuan.chen@linux.dev, netdev@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH net v4 1/2] inet: reject unhashed sockets during established lookups Date: Mon, 26 Oct 2026 09:37:44 +0900 Message-ID: <20261026003804.61923-2-imv4bel@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261026003804.61923-1-imv4bel@gmail.com> References: <20261026003804.61923-1-imv4bel@gmail.com> X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit TCP established ehash lookups are lockless. The socket caches involved use SLAB_TYPESAFE_BY_RCU, so memory can be reused before an RCU reader that retained its old address has finished. After a tuple match, __inet_lookup_established() and __inet6_lookup_established() acquire a reference and repeat the tuple check. They do not check whether the new object is hashed. If the address is reused for a socket with the same tuple, the lookup can acquire a reference to the new object and return it while its nulls node is unhashed. A PoC that drives reuse with a SYN cookie request socket reproduced the crash. The new request socket is unhashed and has a NULL rsk_listener. A lookup that had loaded the address of the old request socket acquired the reference published by tcp_get_cookie_sock() and returned the new object. tcp_v4_rcv() then read sk_state through the NULL listener. The resulting crash was: BUG: kernel NULL pointer dereference, address: 0000000000000012 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page ... Oops: Oops: 0000 [#1] SMP NOPTI CPU: 4 UID: 0 PID: 0 Comm: swapper/4 Not tainted 7.3.0-00591-g0e135910deec #1 PREEMPT(lazy) ... RIP: 0010:tcp_v4_rcv+0x44e/0x1280 ... R10: 0000000000000001 R11: 00000000024ca8c0 R12: 0000000000000000 ... CR2: 0000000000000012 CR3: 0000000103d50004 CR4: 0000000000770ef0 ... Call Trace: ? raw_local_deliver+0xae/0x240 ip_protocol_deliver_rcu+0x2d/0x180 ip_local_deliver_finish+0x84/0x100 ip_sublist_rcv_finish+0x5f/0x70 ip_sublist_rcv+0x12a/0x1d0 ip_list_rcv+0xfd/0x130 __netif_receive_skb_list_core+0x223/0x250 netif_receive_skb_list_internal+0x1d2/0x2c0 ? try_fill_recv+0x39/0x7b0 napi_complete_done+0x74/0x170 virtnet_poll+0x445/0x600 __napi_poll+0x27/0x1e0 net_rx_action+0x2fe/0x3b0 handle_softirqs+0xc2/0x2c0 __irq_exit_rcu+0x74/0xd0 common_interrupt+0x7f/0x90 ... Kernel panic - not syncing: Fatal exception in interrupt After taking a reference, check whether the nulls node is unhashed in both IPv4 and IPv6 established lookups. If it is unhashed or the tuple no longer matches, drop the reference and restart the lookup. Lookups racing with the TIME_WAIT hashdance, or with a request being replaced by its child, now restart and find the new socket instead of returning the old one. Request sockets that were never inserted into ehash can have a nonzero refcount, and a stale lookup can hold a transient reference. Therefore, when SYN cookie, Fast Open, and request migration paths fail after setting a nonzero refcount, release the references held by those paths with reqsk_put() instead of freeing the request directly. Fixes: 079096f103fa ("tcp/dccp: install syn_recv requests into ehash table") Cc: stable@vger.kernel.org Signed-off-by: Hyunwoo Kim Reviewed-by: Eric Dumazet --- net/ipv4/inet_connection_sock.c | 10 +++++++--- net/ipv4/inet_hashtables.c | 5 +++-- net/ipv4/syncookies.c | 2 ++ net/ipv4/tcp_input.c | 4 +++- net/ipv6/inet6_hashtables.c | 4 +++- 5 files changed, 18 insertions(+), 7 deletions(-) diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c index 6a30f11384547..bd0bad96c93c3 100644 --- a/net/ipv4/inet_connection_sock.c +++ b/net/ipv4/inet_connection_sock.c @@ -1136,10 +1136,14 @@ static void reqsk_timer_handler(struct timer_list *t) */ if (nreq) { __NET_INC_STATS(net, LINUX_MIB_TCPMIGRATEREQFAILURE); + /* The timer was not armed, drop its reference here. */ + reqsk_put(nreq); no_ownership: reqsk_migrate_reset(nreq); reqsk_queue_removed(queue, nreq); - __reqsk_free(nreq); + /* Drop the temporary reference and the one reserved for ehash. */ + reqsk_put(nreq); + reqsk_put(nreq); } drop: @@ -1447,7 +1451,7 @@ struct sock *inet_csk_complete_hashdance(struct sock *sk, struct sock *child, __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); reqsk_migrate_reset(nreq); - __reqsk_free(nreq); + reqsk_put(nreq); } else if (inet_csk_reqsk_queue_add(sk, req, child)) { return child; } @@ -1502,7 +1506,7 @@ void inet_csk_listen_stop(struct sock *sk) __NET_INC_STATS(sock_net(nsk), LINUX_MIB_TCPMIGRATEREQFAILURE); reqsk_migrate_reset(nreq); - __reqsk_free(nreq); + reqsk_put(nreq); } rcu_read_unlock(); diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c index ba0faa9ae2bb3..58d54965036a2 100644 --- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c @@ -552,8 +552,9 @@ struct sock *__inet_lookup_established(const struct net *net, if (likely(inet_match(net, sk, acookie, ports, dif, sdif))) { if (unlikely(!refcount_inc_not_zero(&sk->sk_refcnt))) goto out; - if (unlikely(!inet_match(net, sk, acookie, - ports, dif, sdif))) { + if (unlikely(hlist_nulls_unhashed_lockless(&sk->sk_nulls_node) || + !inet_match(net, sk, acookie, ports, dif, + sdif))) { sock_gen_put(sk); goto begin; } diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c index 73e1297681847..6440305615378 100644 --- a/net/ipv4/syncookies.c +++ b/net/ipv4/syncookies.c @@ -218,6 +218,8 @@ struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb, bh_unlock_sock(child); sock_put(child); + reqsk_put(req); + return NULL; } __reqsk_free(req); diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 99baf14afdfd8..3583867487d7f 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -7777,7 +7777,9 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops, if (!inet_csk_reqsk_queue_add(sk, req, fastopen_sk)) { bh_unlock_sock(fastopen_sk); sock_put(fastopen_sk); - goto drop_and_free; + /* tcp_disconnect() already dropped one reqsk ref. */ + reqsk_put(req); + goto drop; } READ_ONCE(sk->sk_data_ready)(sk); bh_unlock_sock(fastopen_sk); diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c index b111b51d69fc9..aa5fa1dd062f7 100644 --- a/net/ipv6/inet6_hashtables.c +++ b/net/ipv6/inet6_hashtables.c @@ -108,7 +108,9 @@ struct sock *__inet6_lookup_established(const struct net *net, if (unlikely(!refcount_inc_not_zero(&sk->sk_refcnt))) goto out; - if (unlikely(!inet6_match(net, sk, saddr, daddr, ports, dif, sdif))) { + if (unlikely(hlist_nulls_unhashed_lockless(&sk->sk_nulls_node) || + !inet6_match(net, sk, saddr, daddr, ports, dif, + sdif))) { sock_gen_put(sk); goto begin; } -- 2.43.0