From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-dy1-f170.google.com (mail-dy1-f170.google.com [74.125.82.170]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C4F042E6CC7 for ; Sat, 18 Apr 2026 16:32:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.82.170 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776529942; cv=none; b=M6zAqN7uYWAxDq/Dvs12pFrc+6kSR1yzwXlJK1Y+2c721Yp+uPOA5y0n3ZsGsw99OZthiQc7KNDRgG7cwI2w0qVtXjFNhJGZ94SFSaHHbMfH74Kwgy0EC9hL5Q+O4M1zIh9X7ISWazwlvtr0n+/SK1VzdYCukVjO6UwxqIRdQMg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776529942; c=relaxed/simple; bh=M7B2FiAQ68bmq17gT51ms1yjCM5hrhJ8ivTJGQv6vmI=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=EarGMnSRBZmscgWP/qKHwyUd6GE2Ulb+3vzyCkJ1CqoBkf/hGMFqbQvSpjizRVacucOVs/l/G/L4SElOiDbtPtFGBUgeSBY4M8RAMdtF8vy/YLtZNGOIWih49OI0y1IJvT7lDnDWKXp/2fPrRY0USi8OoqGZo9sUANUiW3lGkm4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=To7DAt54; arc=none smtp.client-ip=74.125.82.170 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="To7DAt54" Received: by mail-dy1-f170.google.com with SMTP id 5a478bee46e88-2e622a9da9cso2429860eec.0 for ; Sat, 18 Apr 2026 09:32:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1776529940; x=1777134740; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=3kxoQx5x6kYpwthdIyOArHGCLCerv98lrw2KVJASpKc=; b=To7DAt54CBNFikgfoMwt+Ya3cmFxCxyD2DJ+v0gEiFWAKqQr/40RXAYp4UXnokoipq IvRQPVJJ6uDmPe1b+7gQ8p25CwcVYdG1iUcHWOLDfN9DtSjsBCfz8+0AfxhCzsqA4L1s 9p0FmEj1ddfNcl8m0/cbT5EEdqe8nvTMVdEoNDix/b8Hp1SZVD7d5EVuSsM6tzMBYSHH 3Yqyt/b+IDS8b6vcmmj2edgVDr5DtFbhhyGBaStBfNh7/xocyY6Fnslep1MdxcZ7g5Gy 2boB6h1Pw/Nlj7A9250L+4IpiitDzpmdzmK/cO8W9LB8x9xDmaNQ3r5xDNGWR448CJax k28Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1776529940; x=1777134740; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=3kxoQx5x6kYpwthdIyOArHGCLCerv98lrw2KVJASpKc=; b=ax83qj7LHysbLvxOZGelyyFFuiVSdUFH1QzElF7X6LAdxhs9PZZgi9hZBKEtLqgUCZ 3Vi+59WRYst7R7w6TlEvnI8oCWpyfkd91SLbQAdLKRTgvkCf1OUeIiMdqZpS/fnx44Th tV2qdSSJL16EElLVaEf2ZQFwkYv1X99FX3Y2t7t1qpanCHTs6zMOPHySD52XBRxVImsZ M7Q6RMjwxRy+Kq+TGHBpWaOUrLxIoCv9O+481w2PIxBAl8XZyJ8N3GqfPkhsiRxEB2ei TqObIhK7/2shrPlTB2EzE4re1OK0akGeImfQf7jEhABpw5WDwen0wl5mbx3sEDhu5izc llAQ== X-Forwarded-Encrypted: i=1; AFNElJ8WEgNoPzZ42icZ14WHPH4b0+iFqr9dL5d9pAoDACARnF539w0ZoQ4oFNLHZMvWjLDI0E30dW53mt/f7hAnkIY=@vger.kernel.org X-Gm-Message-State: AOJu0YxH8yPyKSYw21ZNODApQYydmLJUh2T49y5JsKOD9Vn3ELWDbDAP jeB6HtR44ABagcdWRZeK8dlGmQV8qeOFjGhd2ImsSPbXyaRKdwoynRTC X-Gm-Gg: AeBDieselSf5Rk2/ENtQGAPg2dYhDIklKuMr2dCVtsLrG5igBRnOxnMf7Bxduy5KnQT IXswi2l3xkPkSBEx6//t1UKsahLlQkIbeizGmFEB2QJdPGEpaKohIpx9d2acEAf1jVSO/QINg78 ZUrmk2Zs9d9MW4/AsinHpWnjEdfGbTcOag8TanZqFUpollAZtwXUii8X4fgH2UZpZQewnDS/Slu DP+y3/4FcSkl9TQIbibSyn6oFrN7mUMEjQWQhOukv8pbRBMMMxoImdCaLgE6hxqMpHgcPzYkaMw tP7cn6HcI+g2isEWoUOTo60Jnn/zcNSZ5kO+d3b6JAnVcSr34Q3ZwDfKMv6GetjYrRqndzt0kgE bkRSY/f18cHrBMzEK9ZZfOUockSjtguOvs2wCL2RbSFPt5RWhXayVrZ7/1k6t6wpnD4iruXN0U1 wVkTeY/toFwK5yrIjwXBNRySc5XyYZuYZOhjCt0VGAHt2nNnoAQLJN4hYS+7cwMuEL084rE/ZhH KmcS1sh9EC+HfsNUa+z X-Received: by 2002:a05:7301:5784:b0:2de:c5ca:c1f3 with SMTP id 5a478bee46e88-2e465293dfdmr3688244eec.4.1776529939859; Sat, 18 Apr 2026 09:32:19 -0700 (PDT) Received: from efaec68ba852.tailc0aff1.ts.net ([206.206.192.132]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2e536e54562sm6894368eec.0.2026.04.18.09.32.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 18 Apr 2026 09:32:18 -0700 (PDT) From: Weiming Shi To: Pablo Neira Ayuso , Florian Westphal , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Phil Sutter , Simon Horman , netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org, Xiang Mei , Weiming Shi Subject: [PATCH nf] netfilter: xt_TCPMSS: check skb_dst before path-MTU clamping Date: Sat, 18 Apr 2026 09:30:58 -0700 Message-ID: <20260418163057.2611503-2-bestswngs@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: netfilter-devel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When TCPMSS with CLAMP_PMTU is used via nft_compat in a non-base chain, par->hook_mask is set to 0, bypassing the checkentry hook validation. The target can then run at PRE_ROUTING where skb_dst is NULL, causing a null-ptr-deref in tcpmss_mangle_packet(): KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] RIP: 0010:tcpmss_mangle_packet (include/net/dst.h:219 net/netfilter/xt_TCPMSS.c:105) tcpmss_tg4 (net/netfilter/xt_TCPMSS.c:202) nft_target_eval_xt (net/netfilter/nft_compat.c:87) nft_do_chain (net/netfilter/nf_tables_core.c:287) nf_hook_slow (net/netfilter/core.c:623) Check skb_dst() for NULL before calling dst_mtu(). Fixes: 493618a92c6a ("netfilter: nft_compat: fix hook validation for non-base chains") Reported-by: Xiang Mei Signed-off-by: Weiming Shi --- net/netfilter/xt_TCPMSS.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c index 116a885adb3c..79b5e475e23e 100644 --- a/net/netfilter/xt_TCPMSS.c +++ b/net/netfilter/xt_TCPMSS.c @@ -102,7 +102,12 @@ tcpmss_mangle_packet(struct sk_buff *skb, if (info->mss == XT_TCPMSS_CLAMP_PMTU) { struct net *net = xt_net(par); unsigned int in_mtu = tcpmss_reverse_mtu(net, skb, family); - unsigned int min_mtu = min(dst_mtu(skb_dst(skb)), in_mtu); + unsigned int min_mtu; + + if (!skb_dst(skb)) + return -1; + + min_mtu = min(dst_mtu(skb_dst(skb)), in_mtu); if (min_mtu <= minlen) { net_err_ratelimited("unknown or invalid path-MTU (%u)\n", -- 2.43.0