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 C3AA347CC69 for ; Tue, 1 Sep 2026 11:11:06 +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=1788261069; cv=none; b=rIIRKkR1i1RuyDfISMIe0AIJb426e1bdtrznudyxZ+CW4a7K9llYIBtgKXyg3uVPhjmqGmL14vVOvblumN1jIo9Vhk6meqOtYnIs/W7okEcI8zD7tOzpfSMDXEEzPPIWyBPKAZPFVNsn+WDDTF0uxtI3HTUC/bSsKHO4JZGrhgc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788261069; c=relaxed/simple; bh=N2MoyBygp87+Z+NIDiAMWXLDR+LZmdoNUaOgOhHks5M=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Df8yD3FiBIzwmeogqP1aPGWCmepeGXQ4271ivjdYuEWvCYHKm+oMU11IHC14VxhXWq6RzFm7YaUDgWVgjAaAg3GR+UucDsRdskMSU8DqxnZOAdOKJRAToCJI2RwbdR+2YiEV+EGv92t3X/a8XGRJhQpRrL1m1VQi3ojKm2lAdMo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oeq3PS5z; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="oeq3PS5z" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3A4901F00A3E; Tue, 1 Sep 2026 11:11:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788261064; bh=zMZRUrOisQ40LTXfqy79z/aZ8xo27jnrhzPmjIrvQRM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=oeq3PS5zdjT9QWhklBacSxzFmCh4gY54X2wJmcmbN2I/nHYZIRn2OFubSqUZLCaCy cAB8n6q638qoi7kAU4lTxlYVwOijHRyZFBigx8L7wIFmWDLOH2+JL0EjcT+u5S3iVI xPbjH9fsr0yA43KiKEe39foTEalkXz31kvSZfLKPSZ8ELqCRMeW8zB+hctlDd4eMwZ eQ+lbZCQwxUwSWBlfSpxcxqmJvNIsQQrfLOv7E9Pc+1BeQdlQL5OHv8MWz18+xHAfX TQt9rZn2jalb3azHVLatjg749X3TFubhgqQ3h0f4kWXsM+NgCC4aA1LII8SgZ+Sosy Xk6iFCL/LFmwg== From: Sasha Levin To: stable@vger.kernel.org Cc: Yong Wang , Vega , Ren Wei , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.12.y 6/6] tcp: clamp route advmss to TCP_MIN_MSS Date: Tue, 1 Sep 2026 07:10:41 -0400 Message-ID: <20260901111041.4174429-6-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260901111041.4174429-1-sashal@kernel.org> References: <2026083105-defuse-publisher-6b6c@gregkh> <20260901111041.4174429-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 --- 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(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index 1cc25e0b3bdea..e027de99d48c5 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1560,6 +1560,11 @@ 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 4d2debf02cce7..bf52dfb153073 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -1800,7 +1800,7 @@ 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 7149ddb098409..b04c0cea7093f 100644 --- a/net/ipv4/tcp_minisocks.c +++ b/net/ipv4/tcp_minisocks.c @@ -422,7 +422,7 @@ 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 296102ed4a96a..4e23991c797c0 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -127,7 +127,7 @@ 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; @@ -3764,7 +3764,7 @@ 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(); @@ -3918,7 +3918,7 @@ 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 b6190f09551d5..57b98ba0d9adf 100644 --- a/net/ipv6/tcp_ipv6.c +++ b/net/ipv6/tcp_ipv6.c @@ -1502,7 +1502,7 @@ 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); -- 2.53.0