From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from Chamillionaire.breakpoint.cc (Chamillionaire.breakpoint.cc [91.216.245.30]) (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 A779E13B2B9; Wed, 5 Jun 2024 19:08:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.216.245.30 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717614521; cv=none; b=tmi5XUjNoo/3TpHKeuEGzOxKAzm6mDvy8kiMt1qeoXTjgy4pkthVdvJDecstEMzgUXgNBBYaBG6rCCKU9oxcQIp20YMCy3SJ4m/FTCpW9tsUIQOgjri6aHEeGl3FRV+Vnk30KgQd23ZvwAts+/Zv7zbScSc8Hfd1VRXuqXfxUJk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717614521; c=relaxed/simple; bh=7EnfzMOiEYBQ7hcFoX27M8Thq/+WVF/h4UrPULuDK7E=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=AqSJiSKR+hLoog/KuVCe7Ug3I4qaQ/ABDgV46xpvViGAe9zd9QuzkEMrTECinzMM8mHJiumZmmuh4oomHtAX5MRF5WXiz9NVM34+WycyRS54Yt/tdEIpb+Wdp9ujsZaMuSnmQq3SVYIhs+g5gbLn+OHtg/h2kBIIXaebnBkT6cc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=strlen.de; spf=pass smtp.mailfrom=strlen.de; arc=none smtp.client-ip=91.216.245.30 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=strlen.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=strlen.de Received: from fw by Chamillionaire.breakpoint.cc with local (Exim 4.92) (envelope-from ) id 1sEvzt-00050l-P8; Wed, 05 Jun 2024 21:08:33 +0200 Date: Wed, 5 Jun 2024 21:08:33 +0200 From: Florian Westphal To: Pablo Neira Ayuso Cc: Christoph Paasch , Florian Westphal , Netfilter , Paolo Abeni , netdev@vger.kernel.org, daniel@iogearbox.net, willemb@google.com Subject: Re: [PATCH nf] netfilter: nf_reject: init skb->dev for reset packet Message-ID: <20240605190833.GB7176@breakpoint.cc> References: <20240604120311.27300-1-fw@strlen.de> <20240605181450.GA7176@breakpoint.cc> Precedence: bulk X-Mailing-List: netdev@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: User-Agent: Mutt/1.10.1 (2018-07-13) Pablo Neira Ayuso wrote: [ CC Willem ] > On Wed, Jun 05, 2024 at 08:14:50PM +0200, Florian Westphal wrote: > > Christoph Paasch wrote: > > > > Reported-by: Christoph Paasch > > > > Suggested-by: Paolo Abeni > > > > Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/494 > > > > Signed-off-by: Florian Westphal > > > > > > I just gave this one a shot in my syzkaller instances and am still hitting the issue. > > > > No, different bug, this patch is correct. > > > > I refuse to touch the flow dissector. > > I see callers of ip_local_out() in the tree which do not set skb->dev. > > I don't understand this: > > bool __skb_flow_dissect(const struct net *net, > const struct sk_buff *skb, > struct flow_dissector *flow_dissector, > void *target_container, const void *data, > __be16 proto, int nhoff, int hlen, unsigned int flags) > { > [...] > WARN_ON_ONCE(!net); > if (net) { > > it was added by 9b52e3f267a6 ("flow_dissector: handle no-skb use case") > > Is this WARN_ON_ONCE() bogus? When this was added (handle dissection from bpf prog, per netns), the correct solution would have been to pass 'struct net' explicitly via skb_get_hash() and all variants. As that was likely deemed to be too much code churn it tries to infer struct net via skb->{dev,sk}. So there are several options here: 1. remove the WARN_ON_ONCE and be done with it 2. remove the WARN_ON_ONCE and pretend net was init_net 3. also look at skb_dst(skb)->dev if skb->dev is unset, then back to 1) or 2) 4. stop using skb_get_hash() from netfilter (but there are likely other callers that might hit this). 5. fix up callers, one by one 6. assign skb->dev inside netfilter if its unset 3 and 2 combined are probably going to be the least invasive. 5 might take some time, we now know two, namely tcp resets generated from netfilter and igmp_send_report(). No idea if there are more. I dislike 3) mainly because of the 'guess the netns' design, not because it adds more code to a way too large function however, so maybe its acceptable?