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([5.255.118.7]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6b009c6a4fdsm1176582a12.5.2026.10.08.03.04.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Oct 2026 03:04:41 -0700 (PDT) From: Theodor Arsenij Larionov Trichkine To: edumazet@kernel.org, kuniyu@google.com, pabeni@redhat.com, willemb@google.com, davem@davemloft.net, kuba@kernel.org Cc: horms@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Theodor Arsenij Larionov Trichkine Subject: [PATCH net] net: use the full socket in sk_mc_loop() Date: Thu, 8 Oct 2026 13:04:23 +0300 Message-Id: <20261008100423.1256884-1-theodorlarionov@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit tcp_make_synack() sets skb->sk of a SYN-ACK to the request socket. If the SYN-ACK destination is multicast, ip_mc_output() calls sk_mc_loop() on it, and inet_test_bit(MC_LOOP, sk) reads inet_flags, which is past the end of the smaller request_sock object. KASAN reports a slab-out-of-bounds (or slab-use-after-free) read in sk_mc_loop() from tcp_v4_send_synack() when a SYN with a multicast source address reaches a listener. Map the socket to the full socket before reading its flags. Fixes: ca6fb0651883 ("tcp: attach SYNACK messages to request sockets instead of listener") Signed-off-by: Theodor Arsenij Larionov Trichkine --- net/core/sock.c | 1 + 1 file changed, 1 insertion(+) diff --git a/net/core/sock.c b/net/core/sock.c index e8551df8330f..1302c1e848b2 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -769,6 +769,7 @@ bool sk_mc_loop(const struct sock *sk) { if (dev_recursion_level()) return false; + sk = sk_const_to_full_sk(sk); if (!sk) return true; /* IPV6_ADDRFORM can change sk->sk_family under us. */ base-commit: 6d25ffca055a77787c21a36b66c253f76239411b -- 2.34.1