From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.netfilter.org (mail.netfilter.org [217.70.190.124]) (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 232603D649F; Sat, 16 May 2026 11:56:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.70.190.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778932601; cv=none; b=A4WMlN/4Vk7lwdpQioPmKs4O+j+WfZGnxz1Kax3tJlLFpCeEmcmoTkdGM90zMaW3LMfb4hBWKmVCG06PKWfIUzcU88JLZR1tykt5MMufTgUBfPe9yFN1JdDus5x+DBnnUJTcleuYkZFhllvA9hGum0qhU9C4vVQe/LN/Q+9R/qk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778932601; c=relaxed/simple; bh=fUhc3No5F31SupMyXeBkRp+8c9BKgzQXYGX99CL2u1g=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=CyCyF61F1oNxFtDHeMh+s2gOFiYYpTHcqTjvWX+qKClazd1ytUHB9g87mRGNt/PZWG0/PyqiOeJLWn9tOsYI8DaVcyfw1FAEd9yDrHo/VefEnpGLhIHeH8HOPhz3XpX7bb+bGyuwe3y8e+BuQhaSGnf4VNMmWMpRx0jKGR+0CvE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=netfilter.org; spf=pass smtp.mailfrom=netfilter.org; dkim=pass (2048-bit key) header.d=netfilter.org header.i=@netfilter.org header.b=QZcWZrEV; arc=none smtp.client-ip=217.70.190.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=netfilter.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=netfilter.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=netfilter.org header.i=@netfilter.org header.b="QZcWZrEV" Received: from localhost.localdomain (mail-agni [217.70.190.124]) by mail.netfilter.org (Postfix) with ESMTPSA id 84426601A5; Sat, 16 May 2026 13:56:32 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=netfilter.org; s=2025; t=1778932593; bh=57GA0S6LBPkf3G9fBfZQH51PjmOpFsu1dMlcjI//taQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=QZcWZrEV8G+R0z7LC+Xjyr0XHySTq6TbO8dnMyL3A16cDXR+zxvF9xYiBpABeVs8H 3+QGXYln8vkZiuXSwHtUOm/mpSWD8QPw6K0KYsGLpSTA5do33dAjVdTw3u1volpLVB m06lF2afv1QrcqnkpIIOXXkiPKA9BupX4qCIDqEuNRy1jCNwxNwlxEIl2j2hNnsZ49 rO0xgMcBz+qzqceVsIKe7ROkvpsqC78DxBy4wICIGzc+aNCSh3FoGdr93aBIldWxRR YdOoyE9sa2qFIzEjewKL6Tr8jeAEuF1h9fMpiAlXA0bD8oOIl+mzf0UelJls8LFnt7 tMGUGexRSs74Q== From: Pablo Neira Ayuso To: netfilter-devel@vger.kernel.org Cc: davem@davemloft.net, netdev@vger.kernel.org, kuba@kernel.org, pabeni@redhat.com, edumazet@google.com, fw@strlen.de, horms@kernel.org Subject: [PATCH net 01/12] netfilter: nf_conntrack_helper: fix possible null deref during error log Date: Sat, 16 May 2026 13:56:16 +0200 Message-ID: <20260516115627.967773-2-pablo@netfilter.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260516115627.967773-1-pablo@netfilter.org> References: <20260516115627.967773-1-pablo@netfilter.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Florian Westphal Reported by sashiko: there is a small race window. If a helper module is unloaded or a userspace-defined helper is removed, nf_conntrack_helper_unregister() sets ->helper to NULL. Handle this safely. This needs a second patch to close related race during nf_conntrack_helper_unregister(). Fixes: b20ab9cc63ca ("netfilter: nf_ct_helper: better logging for dropped packets") Signed-off-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conntrack_helper.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/net/netfilter/nf_conntrack_helper.c b/net/netfilter/nf_conntrack_helper.c index b594cd244fe1..17e971bd4c74 100644 --- a/net/netfilter/nf_conntrack_helper.c +++ b/net/netfilter/nf_conntrack_helper.c @@ -321,8 +321,8 @@ __printf(3, 4) void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct, const char *fmt, ...) { + const char *helper_name = "(null)"; const struct nf_conn_help *help; - const struct nf_conntrack_helper *helper; struct va_format vaf; va_list args; @@ -331,14 +331,17 @@ void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct, vaf.fmt = fmt; vaf.va = &args; - /* Called from the helper function, this call never fails */ help = nfct_help(ct); + if (help) { + const struct nf_conntrack_helper *helper; - /* rcu_read_lock()ed by nf_hook_thresh */ - helper = rcu_dereference(help->helper); + helper = rcu_dereference(help->helper); + if (helper) + helper_name = helper->name; + } nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL, - "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf); + "helper %s dropping packet: %pV ", helper_name, &vaf); va_end(args); } -- 2.47.3