From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792492304; b=ePwf5ceOIrcIwamM1LUy8Dwau1AmZGn5nvynA+y3kLwGk8m5nh3q/E2kQwgj6Z9b/DkV gS1nvrOc5m+NNLjFA33ICQ/v8Fl/g3+VTq1ozQFwuR/gqYKxJ97dLGqjxDnfHZByZ4vRV tBGSaHvm5qJiTG+ucK43jnJIgQGLgkyM9KVMBVdHL+xzXFSHCxSxTA0yNJDXRhRKsNpPi goUjwIxSPT0ijLAwyqnmfayElh/Gg+BwbI8jW7HYU0m0zFlYFD6eAEsoSwMWzPpoCLXQ4 iyao1suKhccC4vzIodzmVPcyAOoFxOjMWnyW4M004j9gZX4dx2gqkkHOzfrvIRs7G0A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792492304; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:Content-Language:From:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=aW+tUhGIytr6myAG/haqiFo8CoeHUsC4Au7jENp7FB0=; b=Stl5wCs28Hmd0nSs9d0xNKzRMaVuUVBoBfZsJmNKCN2s0gnkW4ThfnCLhlSZkXwdaTdB bFCuOGXUlt+1mFL0HJyf/k4RPcHVv6X/9z7Gwr4/YT9qBMgucz7zwhONWiMZIgboXiNP6 FLWy6O9ju/AHJfAoXKGywYeaUL9kJHUb9DKTlwiy3p5KjHvSEpvELzJDzVsAbBQHXERl8 X5y6J8p0zFr/qDq0u+uIvlrpBBQiLJRCccftHxDnS5x/oRR8fYdFFliK1yX7Jkm+mKZXp nCTo21kUu+6KteMDdOqQRAZWLSvG6bu1v1NlybuCM5USgzEyVaX/QT4tOU8WlXk7tMg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=fdIsAXuY; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5FE31606A31A; Tue, 20 Oct 2026 10:31:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=fdIsAXuY Received: by smtp.kernel.org (Postfix) with ESMTPSA id 88FD21F000C4; Tue, 20 Oct 2026 10:31:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792492304; bh=aW+tUhGIytr6myAG/haqiFo8CoeHUsC4Au7jENp7FB0=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=fdIsAXuYNFCvTxZEqUFxtcgLs7ZMUHxO4dBU2zUuVXo8Y32rD52ephxinNlUuIu3u gGBRPorpuUwTZnCjWKqEZMkSC1qPaYfr5ibX6PakxqzZZY+riitZKwvUSrF3t20u7T h4UA9C6LIUYm80TkiBDiFtnzLPj9nAsZxAjm8h6gG2E+uizSFZ47WspBg+5VOTrXnk wYuBOH4BF3oOpTgFtuDC8isv6h/R9eFPaXCp9DbmQTmK/EscMqfaPtR26bN4UxU0/t 38eo7Zotu521jTaRcxY09MfJsOLuG7CJFuC+xeWLONA3dyKCNLZjRcim0bVQTunTsB wIY2MHR+aCLXg== Message-ID: Date: Tue, 20 Oct 2026 12:31:39 +0200 X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net v5] net: ipv4: add zero check for snd_cwnd_clamp To: Kaho Jiang , ncardwell@google.com, kuniyu@google.com, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, edumazet@kernel.org Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, co+71b6509cb791e531@bugs.sh References: <20261019222531.1073-1-kj2864@nyu.edu> Content-Language: en-US From: Eric Dumazet In-Reply-To: <20261019222531.1073-1-kj2864@nyu.edu> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10/20/26 00:25, Kaho Jiang wrote: > User can pass zero to snd_cwnd_clamp via RTAX_CWND type. > This could lead to division of zero error if not checked properly. > > Oops: divide error: 0000 [#1] SMP KASAN NOPTI > Call Trace: > > tcp_reno_cong_avoid (net/ipv4/tcp_cong.c:510 (discriminator 1)) > tcp_ack (net/ipv4/tcp_input.c:3517 net/ipv4/tcp_input.c:3873 net/ipv4/tcp_input.c:4440) > tcp_rcv_established (net/ipv4/tcp_input.c:6685) > tcp_v4_do_rcv (net/ipv4/tcp_ipv4.c:1854) > tcp_v4_rcv (net/ipv4/tcp_ipv4.c:2248) > ip_protocol_deliver_rcu (net/ipv4/ip_input.c:207 (discriminator 1)) > ip_local_deliver_finish (net/ipv4/ip_input.c:241 (discriminator 1)) > ip_local_deliver (./include/linux/netfilter.h:325 ./include/linux/netfilter.h:319 net/ipv4/ip_input.c:262) > ip_rcv (./include/net/dst.h:481 (discriminator 6) net/ipv4/ip_input.c:492 (discriminator 6) ./include/linux/netfilter.h:325 (discriminator 6) ./include/li) > __netif_receive_skb_one_core (net/core/dev.c:6297 (discriminator 4)) > __netif_receive_skb (net/core/dev.c:6410) > process_backlog (net/core/dev.c:6761) > __napi_poll.constprop.0 (net/core/dev.c:7830) > net_rx_action (net/core/dev.c:7893 net/core/dev.c:8050) > handle_softirqs (kernel/softirq.c:645) > __irq_exit_rcu (kernel/softirq.c:679 kernel/softirq.c:519 kernel/softirq.c:758) > irq_exit_rcu (kernel/softirq.c:775) > sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1062 (discriminator 35) arch/x86/kernel/apic/apic.c:1062 (discriminator 35)) > RIP: 0010:tcp_cong_avoid_ai (net/ipv4/tcp_cong.c:482) > > Fix by checking if user pass in zero as parameter, > if so reject the value zero. > > Fixes: 814d488c6126 ("tcp: fix the timid additive increase on stretch ACKs") > Cc: stable@vger.kernel.org > Reported-by: co+71b6509cb791e531@bugs.sh > Assisted-by: LLM > Signed-off-by: Kaho Jiang > --- > include/net/tcp.h | 2 +- > net/ipv4/metrics.c | 4 ++++ > 2 files changed, 5 insertions(+), 1 deletion(-) > > diff --git a/include/net/tcp.h b/include/net/tcp.h > index 4416cdf9bf30..9f605d9ecb35 100644 > --- a/include/net/tcp.h > +++ b/include/net/tcp.h > @@ -1522,7 +1522,7 @@ static inline u32 tcp_snd_cwnd(const struct tcp_sock *tp) > static inline void tcp_snd_cwnd_set(struct tcp_sock *tp, u32 val) > { > WARN_ON_ONCE((int)val <= 0); > - WRITE_ONCE(tp->snd_cwnd, val); > + WRITE_ONCE(tp->snd_cwnd, max(val, 1U)); No. Please do not hide bugs. I repeat : Do not change tcp_snd_cwnd_set() > } > > static inline bool tcp_in_slow_start(const struct tcp_sock *tp) > diff --git a/net/ipv4/metrics.c b/net/ipv4/metrics.c > index ad40762a8b38..cb36686973e5 100644 > --- a/net/ipv4/metrics.c > +++ b/net/ipv4/metrics.c > @@ -54,6 +54,10 @@ static int ip_metrics_convert(struct nlattr *fc_mx, > NL_SET_ERR_MSG(extack, "Unknown flag set in feature mask in metrics attribute"); > return -EINVAL; > } > + if (type == RTAX_CWND && !val) { > + NL_SET_ERR_MSG(extack, "RTAX_CWND must be greater than zero"); > + return -EINVAL; > + } > metrics[type - 1] = val; > } But is it really fixing anything ? I guess this is why you added the max() in tcp_snd_cwnd_set() because you did not understand the issue. An unlocked CWND of zero is harmless. I think a better fix would be: diff --git a/net/ipv4/metrics.c b/net/ipv4/metrics.c index ad40762a8b38379e4ccdc505e3885adb8dfff763..b7f8c47f72f9707adb4ef4dde5558af23b46a502 100644 --- a/net/ipv4/metrics.c +++ b/net/ipv4/metrics.c @@ -60,6 +60,12 @@ static int ip_metrics_convert(struct nlattr *fc_mx, if (ecn_ca) metrics[RTAX_FEATURES - 1] |= DST_FEATURE_ECN_CA; + if ((metrics[RTAX_LOCK - 1] & (1 << RTAX_CWND)) && + !metrics[RTAX_CWND - 1]) { + NL_SET_ERR_MSG(extack, "Locked cwnd metric must be non zero"); + return -EINVAL; + } + return 0; } Note that my email address is edumazet@kernel.org Make sure to refresh your git tree, because git should have handled the change automatically. pw-bot: cr