From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.netfilter.org (mail.netfilter.org [217.70.188.207]) by smtp.subspace.kernel.org (Postfix) with ESMTP id B1593163 for ; Thu, 9 Jan 2025 00:03:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.70.188.207 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736381016; cv=none; b=XWsFnK/iF3IY9hIlmRDglHa907DNA8veaeMjL/C4nwZ4jTr8lEx7xJDNuIsderpnlY24y94fZp8n9bwPGlLXqcAO+FR8GoDqSU7hBZik/UxJPxi7m6su0f0Katml9zQQn9hYzbznTEaXM0ceMnJRXOICe+uDrntAa7S+8MxOpBA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736381016; c=relaxed/simple; bh=JZ2LHp4rTtj8Ku7Hz364Mxvd7/Iv4bpj+olylwf7cag=; h=Date:From:To:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=WBe6rQCDBKjjdKYO3fGXyEJt6iCa84FUI70iHTychP08z+inZomHngGnEyQUnOvYN84VymXrQwZp4ZKRqlYCPogNFBzdhuv/IglM8AfDtVi2irhtRt6LBVADgsMSC5StVo6p4+nWzNMs/NG/tLyiRSEhP29zVg4s5YvyjZgCCAo= 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; arc=none smtp.client-ip=217.70.188.207 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 Date: Thu, 9 Jan 2025 01:03:25 +0100 From: Pablo Neira Ayuso To: Phil Sutter , Alyssa Ross , netfilter-devel@vger.kernel.org, Joshua Lant Subject: Re: [PATCH nftables] include: fix for musl with iptables v1.8.11 Message-ID: References: <20241219231001.1166085-2-hi@alyssa.is> Precedence: bulk X-Mailing-List: netfilter-devel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Hi Phil, On Thu, Jan 09, 2025 at 12:49:53AM +0100, Phil Sutter wrote: > Hi Pablo, > > On Thu, Jan 09, 2025 at 12:34:01AM +0100, Pablo Neira Ayuso wrote: > > On Fri, Dec 20, 2024 at 01:33:42PM +0100, Phil Sutter wrote: > > > On Fri, Dec 20, 2024 at 01:07:56PM +0100, Alyssa Ross wrote: > > > > On Fri, Dec 20, 2024 at 12:50:42PM +0100, Phil Sutter wrote: > > > > > Hi Alyssa, > > > > > > > > > > On Fri, Dec 20, 2024 at 12:10:02AM +0100, Alyssa Ross wrote: > > > > > > Since iptables commit 810f8568 (libxtables: xtoptions: Implement > > > > > > XTTYPE_ETHERMACMASK), nftables failed to build for musl libc: > > > > > > > > > > > > In file included from /nix/store/bvffdqfhyxvx66bqlqqdmjmkyklkafv6-musl-1.2.5-dev/include/netinet/et… > > > > > > from /nix/store/kz6fymqpgbrj6330s6wv4idcf9pwsqs4-iptables-1.8.10-de… > > > > > > from src/xt.c:30: > > > > > > /nix/store/bvffdqfhyxvx66bqlqqdmjmkyklkafv6-musl-1.2.5-dev/include/netinet/if_ether.h:115:8: error: redefinition of 'struct ethhdr' > > > > > > 115 | struct ethhdr { > > > > > > | ^~~~~~ > > > > > > In file included from ./include/linux/netfilter_bridge.h:8, > > > > > > from ./include/linux/netfilter_bridge/ebtables.h:1, > > > > > > from src/xt.c:27: > > > > > > /nix/store/bvffdqfhyxvx66bqlqqdmjmkyklkafv6-musl-1.2.5-dev/include/linux/if_ether.h:173:8: note: originally defined here > > > > > > 173 | struct ethhdr { > > > > > > | ^~~~~~ > > > > > > > > > > > > The fix is to use libc's version of if_ether.h before any kernel > > > > > > headers, which takes care of conflicts with the kernel's struct ethhdr > > > > > > definition by defining __UAPI_DEF_ETHHDR, which will tell the kernel's > > > > > > header not to define its own version. > > > > > > > > > > What I don't like about this is how musl tries to force projects to not > > > > > include linux/if_ether.h directly. From the project's view, this is a > > > > > workaround not a fix. > > > > > > > > My understanding is that it's a general principle of using any libc on > > > > Linux that if there's both a libc and kernel header for the same thing, > > > > the libc header should be used. libc headers will of course include > > > > other libc headers in preference to kernel headers, so if you also > > > > include the kernel headers you're likely to end up with conflicts. > > > > Whether conflicts occur in any particular case depends on how a > > > > particular libc chooses to expose a particular kernel API. I could be > > > > misremembering, but I believe the same thing can happen with Glibc — > > > > some headers under sys/ cause conflicts with their corresponding kernel > > > > headers if both are included. While this case is musl specific, I > > > > think the principle applies to all libcs. > > > > > > While this may be true for the vast majority of user space programs, > > > netfilter tools and libraries are a bit special in how close they > > > interface with the kernel. Not all netfilter-related kernel API is > > > exposed by glibc, for instance. Including (some) kernel headers is > > > therefore unavoidable, and (as your patch shows) order of inclusion > > > becomes subtly relevant in ways which won't show when compile-testing > > > against glibc only. > > > > > > > > > Signed-off-by: Alyssa Ross > > > > > > --- > > > > > > A similar fix would solve the problem properly in iptables, which was > > > > > > worked around with 76fce228 ("configure: Determine if musl is used for build"). > > > > > > The __UAPI_DEF_ETHHDR is supposed to be set by netinet/if_ether.h, > > > > > > rather than manually by users. > > > > > > > > > > Why does 76fce228 not work for you? > > > > > > > > It does work, but that's a fix for iptables. This is a fix for > > > > nftables. I could have submitted a copy of the iptables fix, but I > > > > don't think it's the best fix due to its reliance on internal macros > > > > that are not part of the public interface. > > > > > > Ah, sorry! Patch subject and description managed to confuse me. > > > > > > Pablo, what's your opinion? Maybe we should strive for the same solution > > > for the problem in all netfilter user space, so either take what we have > > > in iptables or adjust iptables to what nftables decides how things > > > should be? > > > > I see, you mean to use this (from iptables): > > > > commit 76fce22826f8e860b5eb5b5a2463040c17ff85da > > Author: Joshua Lant > > Date: Wed Aug 28 13:47:31 2024 +0100 > > > > configure: Determine if musl is used for build > > > > and adapt to use it from nftables (and everywhere else). > > > > Alyssa's patch is more simple, but it is mangling a cache kernel > > header. > > Right, so the fixing should start in kernel repo, then update the cached > header in nftables. > > > Is this configure.ac workaround needed everywhere in the netfilter.org > > trees to make musl happy? > > AIUI, only in those including linux/if_ether.h directly. ;) Hm. I am looking at include/uapi/linux/netfilter_bridge.h and... #include #include #include #include #include I don't understand why all those #include need to be there, this header file contains only defines an enumeration... git annotate takes me to: 607ca46e97a1 ("UAPI: (Scripted) Disintegrate include/linux") Silly question: Does it break any netfilter userspace software if #include is moved from that kernel header file to to the non-uapi netfilter_bridge.h header file. > Though there is such include in nftables' src/payload.c which remains > unchanged by Alyssa's patch. Not sure if intentional, maybe there are > factors which make the include harmless. This is userspace, I guess we can replace it with userspace netinet/ header variant. > > I don't see any better option at this stage. > > According to a quick grep, there are currently six spots including > linux/if_ether.h (including one cached kernel header). I like about the > configure hack that it avoids breaking musl by accident via some > seemingly unrelated patch. Just one less thing to keep in mind, but this > is just me. I appreciate other opinions! Agreed, avoiding the configure kludge would be good. > Cheers, Phil > > PS: Can't we just fix musl instead? *hides*