From mboxrd@z Thu Jan 1 00:00:00 1970 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 E3795408039 for ; Mon, 31 Aug 2026 12:53:28 +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=1788180811; cv=none; b=c7ZPUARk5GOE8JS8JO+dGEWz9opzmzNzaTrcUS/Qa2/W7qq0WP1uAsAVC9pL7OSlnoHScajiQoUaRHVupRUUz1iOcDZKQQwkBusGpVL2LYBJZgKY1u8CsZATeOvwNerPRvTpz+01KCfhfm4EwRxTJHHOkJoAid0We8dh5HV+wD0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788180811; c=relaxed/simple; bh=g0KDQse8mzHo/FYK4Ov6HlsIgZfEO+jM59wC0FLedUM=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=MI5OzRdMec5Xhftg2GJf+z6qSU8c20tHS9SyksComUkOeqOgiKMpX35kTpgkPM4CnQ2ivTWS57j8k4D4T8cxUTBU8s+HvIffsipjH3nNxnk0Y71ipTlIagv3D+7CDeRNYMnOfLFrvEXoIldy7jqNTXvOdBYPylp2fMeEFVyEOx8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=R/IuICEn; 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="R/IuICEn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A28E31F00A3D; Mon, 31 Aug 2026 12:53:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1788180808; bh=loz7QBIYTLupuSuKllfozgaizpDwulZK4JDOXZWnV6g=; h=Subject:To:Cc:From:Date; b=R/IuICEnewdz3uFO8lXkauNYDXqloAtxaDiFAUT34btbO3xhgTuzBXE7XOGthoLmt WRfEOocC6MN97P2zO7MC/lJPkOO9bo0btOhM4sGDgQ2hDmYn/EqvaZNgJ33WTLERyC HA8nHS/X7ZZ2d/85k6HFvcQhQ1CUDYfdyyCkBbzc= Subject: FAILED: patch "[PATCH] tcp: clamp route advmss to TCP_MIN_MSS" failed to apply to 6.1-stable tree To: edragain@163.com,kuba@kernel.org,vega@nebusec.ai,weir@nebusec.ai Cc: From: Date: Mon, 31 Aug 2026 14:53:06 +0200 Message-ID: <2026083106-glider-shiftless-2e30@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x 870a9e42ecc6fe1b8c25d87af043cb0d9c178fe1 # git commit -s git send-email --to '' --in-reply-to '2026083106-glider-shiftless-2e30@gregkh' --subject-prefix 'PATCH 6.1.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 870a9e42ecc6fe1b8c25d87af043cb0d9c178fe1 Mon Sep 17 00:00:00 2001 From: Yong Wang Date: Wed, 19 Aug 2026 23:22:04 +0800 Subject: [PATCH] tcp: clamp route advmss to TCP_MIN_MSS 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 diff --git a/include/net/tcp.h b/include/net/tcp.h index 2c5b889530b5..670c20876f26 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1782,6 +1782,11 @@ static inline int tcp_full_space(const struct sock *sk) 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); diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index 190c7af4cf92..9f053eb8b46e 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -1736,7 +1736,7 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb, 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); diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c index 12254e6eb2f3..f3fa0b18eda0 100644 --- a/net/ipv4/tcp_minisocks.c +++ b/net/ipv4/tcp_minisocks.c @@ -440,7 +440,7 @@ void tcp_openreq_init_rwin(struct request_sock *req, 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); diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index fcaa04e65189..f2709d585edb 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -143,7 +143,7 @@ static __u16 tcp_advertise_mss(struct sock *sk) 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; @@ -3972,7 +3972,7 @@ struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst, } 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(); @@ -4128,7 +4128,7 @@ static void tcp_connect_init(struct sock *sk) 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); diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c index 9e9155b1b3aa..df9c29eb5c1f 100644 --- a/net/ipv6/tcp_ipv6.c +++ b/net/ipv6/tcp_ipv6.c @@ -1487,7 +1487,7 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff * 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);