Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1CACE49D59C; Thu, 17 Sep 2026 18:58:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789671532; cv=none; b=TpCzQs/ccu3P4R+NyGmeVtSoy2VwCJr5K7f/hOyhWbtOls2t7RHFXswiOlWrrl0c6+ZY22iqz3aW1PUa4Vy8+BLng7G9mc1ulZH0QrebMqCO2skyoiYUwDJykS3EPymdBacAJEKoTQbXo+kMXLkoDdUO026cUM909qfFReoBpro= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789671532; c=relaxed/simple; bh=Wuezl2kaYoD2IRCYfH93NDlhJxk2bWTrgFlPmhTq+tg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=OpniPPwjrO2UuRcu0ir+0TZ5aZMg9i1TWmAB90R506pJAAtzXxrqiknHv1SWArjrTW5ftl0KyNbb5HTv6dqUxs7ZQaG0fDAkEmLakeWCY5Ax4ElscGA9ttEcRUMuKneQkNHmuXRSP40btUFcc+E//1JFGumlbH79vhvOcFP3MFk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=ZgSZEv0o; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="ZgSZEv0o" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5538E1F000FF; Thu, 17 Sep 2026 18:58:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789671531; bh=lsSrkMBAiz6T9D2YJ/qWeW5qR1A7EE1s7V6eQhX6okY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=ZgSZEv0oH0SpTUKMOl8Q66xcSTaF5BN6lPtjF847Tvj40Z+AAZk2Fz1NC5Puhx5sw B0pC1NJfItAaTS6M5zpWv2QOlZQ/X6H4PGHeMoBGd78zwjCqC+V7i4epIdxEVU8QDg 4+tXOHerCk18fYI2UoWmDi3Em6wGNo2p8NUkzV7k= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Vega , Yong Wang , Ren Wei , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.12 0969/1102] tcp: clamp route advmss to TCP_MIN_MSS Date: Thu, 17 Sep 2026 16:15:12 +0100 Message-ID: <20260917151605.009375356@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260917151539.408551884@linuxfoundation.org> References: <20260917151539.408551884@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yong Wang [ Upstream commit 870a9e42ecc6fe1b8c25d87af043cb0d9c178fe1 ] tcp_select_initial_window() assumes that callers never pass an MSS smaller than 1, but route-derived advmss values can violate that assumption. A too-small explicit RTAX_ADVMSS is one way to get there, but it is not the only one. The same divide-by-zero can also be reached through the "default advmss" path when RTAX_ADVMSS is left at 0 and the effective advmss is later driven down by route MTU and min_adv_mss. Introduce a tcp_dst_advmss() helper that clamps route advmss to TCP_MIN_MSS before TCP consumes it, and use it in the TCP paths that derive advmss from dst metrics. This keeps the effective MSS from dropping to zero before tcp_select_initial_window() rounds the receive window. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Reported-by: Vega Signed-off-by: Yong Wang Signed-off-by: Ren Wei Link: https://patch.msgid.link/251eaf8277fa7c66364c9815c5da01662d269181.1787074852.git.edragain@163.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- include/net/tcp.h | 5 +++++ net/ipv4/tcp_ipv4.c | 2 +- net/ipv4/tcp_minisocks.c | 2 +- net/ipv4/tcp_output.c | 6 +++--- net/ipv6/tcp_ipv6.c | 2 +- 5 files changed, 11 insertions(+), 6 deletions(-) --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1561,6 +1561,11 @@ static inline int tcp_full_space(const s return tcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf)); } +static inline u32 tcp_dst_advmss(const struct dst_entry *dst) +{ + return max_t(u32, dst_metric_advmss(dst), TCP_MIN_MSS); +} + static inline void __tcp_adjust_rcv_ssthresh(struct sock *sk, u32 new_ssthresh) { int unused_mem = sk_unused_reserved_mem(sk); --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -1806,7 +1806,7 @@ struct sock *tcp_v4_syn_recv_sock(const tcp_ca_openreq_child(newsk, dst); tcp_sync_mss(newsk, dst4_mtu(dst)); - newtp->advmss = tcp_mss_clamp(tcp_sk(sk), dst_metric_advmss(dst)); + newtp->advmss = tcp_mss_clamp(tcp_sk(sk), tcp_dst_advmss(dst)); tcp_initialize_rcv_mss(newsk); --- a/net/ipv4/tcp_minisocks.c +++ b/net/ipv4/tcp_minisocks.c @@ -422,7 +422,7 @@ void tcp_openreq_init_rwin(struct reques u32 rcv_wnd; int mss; - mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); + mss = tcp_mss_clamp(tp, tcp_dst_advmss(dst)); window_clamp = READ_ONCE(tp->window_clamp); /* Set this up on the first call only */ req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -127,7 +127,7 @@ static __u16 tcp_advertise_mss(struct so int mss = tp->advmss; if (dst) { - unsigned int metric = dst_metric_advmss(dst); + unsigned int metric = tcp_dst_advmss(dst); if (metric < mss) { mss = metric; @@ -3764,7 +3764,7 @@ struct sk_buff *tcp_make_synack(const st } skb_dst_set(skb, dst); - mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); + mss = tcp_mss_clamp(tp, tcp_dst_advmss(dst)); memset(&opts, 0, sizeof(opts)); now = tcp_clock_ns(); @@ -3918,7 +3918,7 @@ static void tcp_connect_init(struct sock if (!tp->window_clamp) WRITE_ONCE(tp->window_clamp, dst_metric(dst, RTAX_WINDOW)); - tp->advmss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); + tp->advmss = tcp_mss_clamp(tp, tcp_dst_advmss(dst)); tcp_initialize_rcv_mss(sk); --- a/net/ipv6/tcp_ipv6.c +++ b/net/ipv6/tcp_ipv6.c @@ -1489,7 +1489,7 @@ static struct sock *tcp_v6_syn_recv_sock tcp_ca_openreq_child(newsk, dst); tcp_sync_mss(newsk, dst6_mtu(dst)); - newtp->advmss = tcp_mss_clamp(tcp_sk(sk), dst_metric_advmss(dst)); + newtp->advmss = tcp_mss_clamp(tcp_sk(sk), tcp_dst_advmss(dst)); tcp_initialize_rcv_mss(newsk);