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 86693204C36 for ; Wed, 8 Jan 2025 23:34:04 +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=1736379247; cv=none; b=TCmR0/p8oQjqW6SX6CgAgff8qfrO+17BvoazYIl5h7Lc+XWBR57SLh/XZrdnTkIMj62gWZc2E5Ljs4m1AVScFOmpIEzky1D0BC97S6RRWvTBrylYfK/pzL6tvLoyFOpfVNPefW17gKdtJAfcK2nJ1KKafbQ0TtEP9g5/Un7nJuk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736379247; c=relaxed/simple; bh=DTIf8XkDkDxofJNkIguYSnbdcGyvEa1gAvnCPjRBYG8=; h=Date:From:To:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=fVTGUXJ7OxIgRGskPLWiJfF+X/9VPLnlCE909KczkmoGu/V1lob6ns1sekGnEJ7hrpxxM1egwhcI4NSM3ZJqmujQE1QqSVcCt+b4+KCKjR1bKqHDTsMk1jTlwC0nYSKkRgCvMcDSCny63N0sp860cWPJZqnBSyEKsRN+g4c/ezI= 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 00:34:01 +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, 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. Is this configure.ac workaround needed everywhere in the netfilter.org trees to make musl happy? I don't see any better option at this stage. Thanks.