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 BA47D4A2611 for ; Tue, 1 Sep 2026 19:28:41 +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=1788290923; cv=none; b=iC8QSHIBNzd3ldoV+7VHokZSwd6uJbdm5IhzF785QoddEoMjCHVsyvYib77wScmOnUzE4lMp7HcUBNjuExCsv49Y/trcNXlyi4irxnK6x3SSr8F9xwcp/F9aUfXswE7jTm7oBdwvwA+NSabHTGgxui2ZMTCjOJZBBLToImepxN4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788290923; c=relaxed/simple; bh=FgWOAVbB31wuIYDirAVCUJpRHKjqbXNFLg2EOuCM+Ng=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GTZpZ2Btg7sW6R5+w/9ZpEYJ4tLjjqLlvNeBWx01Qo73jJqo9PTRF6OzYTFkPN3GB9GclG4Q8yEBdqxvsJWrXFwhIHY04bjdVUzl0a+fEoX0VbgjA3P3AaxIYBYbmOKT5booulY0+ahuUtSkdWodnVS87vDTNXqfLzxYHB5pSHc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IQ67lG7i; 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="IQ67lG7i" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F25511F00ACF; Tue, 1 Sep 2026 19:28:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788290921; bh=OPHs3ArP5PL8zh+CsYIsKI4NvFNRyf/9zqnRtKBRTjw=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=IQ67lG7ixtDu5x/x37HGASLBIks2R2DaOvEEkiele/+OZ2EWhI+c/GsOUFrghArcs bax6FaDIvGn1Bpb1PG3OD9w3ztUAiNx/uLqI6a/tpQrEJmzpzHXdXhykKJbsWosejV JR2GO6RB3AtOAhfaxM2kk3PKxwEFCWv2NQQAnvkMmv/IcwQ+WJeszN+YdidCAFMD1g m+86CV0ZrS6j5m+ehOXqlAfwFxIuFtwTYmWZZNetR5cmR6U+yC1DQIor7I9TuYt8cU BF1iaxNb7b7XmIxjSlF0A8fw/LpR4tILK2c7+FI0lBuELQGNQ9I7TS3VeTE6erm9Zr EaDftRbMAYg7w== From: Sasha Levin To: stable@vger.kernel.org Cc: Yong Wang , Vega , Ren Wei , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.1.y 7/8] tcp: clamp route advmss to TCP_MIN_MSS Date: Tue, 1 Sep 2026 15:28:32 -0400 Message-ID: <20260901192833.1439569-7-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260901192833.1439569-1-sashal@kernel.org> References: <2026083106-glider-shiftless-2e30@gregkh> <20260901192833.1439569-1-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 [ kept `tp->window_clamp` assignment without the unbacked `WRITE_ONCE()` wrapper while applying `tcp_dst_advmss()` substitution ] 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 9632ac801e016..b40ec34a504b0 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1479,6 +1479,11 @@ 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 7be24beed347f..f5c3d228269da 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -1567,7 +1567,7 @@ 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 22b5748a6ee2c..c26306cc6ec30 100644 --- a/net/ipv4/tcp_minisocks.c +++ b/net/ipv4/tcp_minisocks.c @@ -378,7 +378,7 @@ 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 2a4657af3fd51..13726ceda5806 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -125,7 +125,7 @@ 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; @@ -3636,7 +3636,7 @@ 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(); @@ -3753,7 +3753,7 @@ static void tcp_connect_init(struct sock *sk) if (!tp->window_clamp) 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 dd3980655986a..7dfe1ab10b645 100644 --- a/net/ipv6/tcp_ipv6.c +++ b/net/ipv6/tcp_ipv6.c @@ -1352,7 +1352,7 @@ 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