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Wed, 11 Nov 2026 09:47:59 -0800 (PST) Received: from VPN-156-197.vpn.usf.edu ([2607:fe50:0:f802::4046]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-67c589c6f24sm5077708d50.12.2026.11.11.09.47.56 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Wed, 11 Nov 2026 09:47:58 -0800 (PST) From: Juan Agustin Niccolini To: davem@davemloft.net, edumazet@kernel.org, kuba@kernel.org, pabeni@redhat.com Cc: horms@kernel.org, ncardwell@google.com, kuniyu@google.com, josef@toxicpanda.com, jbacik@fb.com, shuah@kernel.org, linux-kselftest@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Juan Agustin Niccolini , stable@vger.kernel.org Subject: [PATCH net v2 1/2] tcp: Fix the SO_REUSEPORT bind cache admitting a conflicting socket Date: Wed, 11 Nov 2026 12:47:03 -0500 Message-ID: <20261111174704.24312-2-juanagusnicco@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261111174704.24312-1-juanagusnicco@gmail.com> References: <20261111174704.24312-1-juanagusnicco@gmail.com> X-Mailing-List: linux-kernel@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 When the port is in the FASTREUSEPORT_STRICT state, inet_csk_get_port() skips the bind conflict check if sk_reuseport_match() finds the new socket's address covered by the socket cached in tb->fast_*. This is only safe if both sockets match on everything inet_bind_conflict() reads. The cache misses some of it: - It does not record sk_bound_dev_if or sk_reuse. - It records the family and IPV6_V6ONLY but never compares them with the new socket, so a cached v6only [::] (or 0.0.0.0) socket covers a dual-stack [::] socket. As a result, an unprivileged user can bind and listen on a port that another user is listening on, for example a dual-stack [::] socket on top of a 0.0.0.0 listener: victim: bind(0.0.0.0:P), listen() attacker: SO_REUSEPORT + IPV6_V6ONLY, bind([::]:P) /* fills cache */ attacker: SO_REUSEPORT, bind([::]:P), listen() /* should fail */ Only take the fast path when the new socket matches the cached one in family, IPV6_V6ONLY, bound device and SO_REUSEADDR. Identical SO_REUSEPORT listeners, the workload this cache was added for, still skip the scan (binding 16384 of them: 9.80 ms before, 9.86 ms after, 5874 ms with the full check every time). Fixes: 637bc8bbe6c0 ("inet: reset tb->fastreuseport when adding a reuseport sk") Cc: stable@vger.kernel.org Signed-off-by: Juan Agustin Niccolini --- include/net/inet_hashtables.h | 2 ++ net/ipv4/inet_connection_sock.c | 15 ++++++++++++--- 2 files changed, 14 insertions(+), 3 deletions(-) diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h index 6e2fe186d0dc..44b7e39a1245 100644 --- a/include/net/inet_hashtables.h +++ b/include/net/inet_hashtables.h @@ -87,6 +87,8 @@ struct inet_bind_bucket { __be32 fast_rcv_saddr; unsigned short fast_sk_family; bool fast_ipv6_only; + unsigned char fast_sk_reuse; + int fast_bound_dev_if; struct hlist_node node; struct hlist_head bhash2; struct rcu_head rcu; diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c index e56beec43877..70b8662b3004 100644 --- a/net/ipv4/inet_connection_sock.c +++ b/net/ipv4/inet_connection_sock.c @@ -420,13 +420,18 @@ static inline int sk_reuseport_match(struct inet_bind_bucket *tb, return 0; if (!uid_eq(tb->fastuid, sk_uid(sk))) return 0; - /* We only need to check the rcv_saddr if this tb was once marked + /* We only need to check the fast_* fields if this tb was once marked * without fastreuseport and then was reset, as we can only know that - * the fast_*rcv_saddr doesn't have any conflicts with the socks on the - * owners list. + * the socket they describe doesn't have any conflicts with the socks + * on the owners list. */ if (tb->fastreuseport == FASTREUSEPORT_ANY) return 1; + if (tb->fast_sk_family != sk->sk_family || + tb->fast_ipv6_only != ipv6_only_sock(sk) || + tb->fast_bound_dev_if != sk->sk_bound_dev_if || + tb->fast_sk_reuse != sk->sk_reuse) + return 0; #if IS_ENABLED(CONFIG_IPV6) if (tb->fast_sk_family == AF_INET6) return ipv6_rcv_saddr_equal(&tb->fast_v6_rcv_saddr, @@ -455,6 +460,8 @@ void inet_csk_update_fastreuse(const struct sock *sk, tb->fast_rcv_saddr = sk->sk_rcv_saddr; tb->fast_ipv6_only = ipv6_only_sock(sk); tb->fast_sk_family = sk->sk_family; + tb->fast_sk_reuse = sk->sk_reuse; + tb->fast_bound_dev_if = sk->sk_bound_dev_if; #if IS_ENABLED(CONFIG_IPV6) tb->fast_v6_rcv_saddr = sk->sk_v6_rcv_saddr; #endif @@ -482,6 +489,8 @@ void inet_csk_update_fastreuse(const struct sock *sk, tb->fast_rcv_saddr = sk->sk_rcv_saddr; tb->fast_ipv6_only = ipv6_only_sock(sk); tb->fast_sk_family = sk->sk_family; + tb->fast_sk_reuse = sk->sk_reuse; + tb->fast_bound_dev_if = sk->sk_bound_dev_if; #if IS_ENABLED(CONFIG_IPV6) tb->fast_v6_rcv_saddr = sk->sk_v6_rcv_saddr; #endif -- 2.43.0