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 11CAB5012BD; Fri, 18 Sep 2026 15:16:00 +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=1789744562; cv=none; b=HOxY4m3KrRVxVwCMU0ZqR1K/+/UCHJ1RN6eExgT1b/8nSEFjLgD9qMm0xvatYe3G2U0Egn7Z15XiRRmsF55HqzNza//vXho3/0yx8+RnEpwtDsdKS0M93veR9Ws1B8vnIG6wKl1zeqvC2ZLN/Yq4UJCcp/UXaKOpcP6ykn1djLM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789744562; c=relaxed/simple; bh=joZY4Up6a26RE7aKPDySANBWpP7OSk0AEhi+9eQ8eeI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=jsKOmJCWbpq2Waso3W2Yb2luE/TC6G+tdV+7ENJb+a0VjFVUo472OC6E5deSzqa/r/shqgC7OzcUdUMHJCfbvoV5cj3XU1P6iHJmyFiEpMG7tUI1BWir1JjU+zobExCwbWHYyHpFG4SQiRmANxqDmgLVZGhQCENCsENkOWfGqxw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nyw66CJ8; 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="nyw66CJ8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6F2941F00899; Fri, 18 Sep 2026 15:15:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789744560; bh=N+JWiSDFunzUFCTH/f0pJTTjhja0GHkiOsC71uOEz5s=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=nyw66CJ8ZRiaQwVH9hSq1T1fLvxLDgaaS/vRGwRLCzKyJdfQ2BLDCLDplJ+T7VG34 vooBozBGyQtkaiFHqpMLseeiI9oCwJ1C0o9UXRtYZHsiUbzANFtSvcExxHJMuAh0OQ 30sKNuMlU5e4mou9L2VSdVZzYh2pk+dhvZz5AMN8lvYV+58vOTAGFoGY7fdra/BuJY JDovFy0mLDLg8AGbGAzXYrAqx+E3qv9P5hvpcaX+ad3uRWxY4C59kBk75BSBDkoxx7 2ZXd9htbTkgcWKdhsxpM14VD0BpixJoHFZPOkRei7g21qjo11MgVFDBG3MRco3rfgx IjC7xQQ11FXaA== Date: Fri, 18 Sep 2026 16:15:56 +0100 From: Simon Horman To: Nguyen Ngoc Thang Cc: netdev@vger.kernel.org, Jamal Hadi Salim , Jiri Pirko , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Paul Blakey , linux-kernel@vger.kernel.org, syzbot+6cc37aba98dac721c415@syzkaller.appspotmail.com Subject: Re: [PATCH net] net/sched: act_ct: don't WARN on benign flow_offload_alloc() failure Message-ID: <20260918151556.GP51261@horms.kernel.org> References: <20260915150816.36487-1-ngocthang2710.1999@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260915150816.36487-1-ngocthang2710.1999@gmail.com> On Tue, Sep 15, 2026 at 10:08:16PM +0700, Nguyen Ngoc Thang wrote: > flow_offload_alloc() returns NULL when the conntrack entry is dying > (e.g. raced with a conntrack flush) or when the GFP_ATOMIC allocation > fails; both are expected under load and neither is a kernel bug. This > path runs from softirq on every committed packet, so with > panic_on_warn=1 an unprivileged user can panic the box just by racing > a conntrack flush against a `tc ... action ct commit` classifier. > > Reproduced with a custom repro under QEMU: a small, fixed set of UDP > flows through `tc filter ... action ct commit` on lo, raced against > threads flooding bare ctnetlink CT_DELETE (flush) requests. Hits > WARNING: net/sched/act_ct.c:437 (tcf_ct_flow_table_add(), inlined > into tcf_ct_act() in this build) within ~15s on the unpatched kernel; > same setup is clean on the patched kernel. The fix itself is > behavior-preserving: both branches already did `goto err_alloc` > before and after, only the WARN is removed. > > Fixes: 64ff70b80fd4 ("net/sched: act_ct: Offload established connections to flow table") > Reported-by: syzbot+6cc37aba98dac721c415@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=6cc37aba98dac721c415 > Signed-off-by: Nguyen Ngoc Thang Reviewed-by: Simon Horman