From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 907ABC43334 for ; Tue, 28 Jun 2022 00:58:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241666AbiF1A6h (ORCPT ); Mon, 27 Jun 2022 20:58:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54374 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242060AbiF1A6e (ORCPT ); Mon, 27 Jun 2022 20:58:34 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 34AA01CFE5; Mon, 27 Jun 2022 17:58:33 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id CD4F7B81C0A; Tue, 28 Jun 2022 00:58:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id BBEABC341C8; Tue, 28 Jun 2022 00:58:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1656377910; bh=x4KMhmowxPAczUMJ6x4nBeCjlIDio89Zlndd34Eza5Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rmtqPrxs/EakAnLyUZ+T1Y6Y2PuUVWE1p/lPmqQBXiapPC1WBd92tcHfgEnTJibSz 8Cqh6wp+mGRPQenFwVH/ncudi5b7Tg0x4DYK6LYwUDkNgU3v8Yk/6Or0HzPxa5QXgF OYkHqjzJwOTAIzA6m0DkNzWrhG6StDZ8wiRdHVw+Wnp/Deq+bcAy4GlTPygKnkBgqV sUW1DRx9UPn831OT0MRefhs1kf7ZlvXFnW9s3XTKUzsS60aUSNGKPAXfxyQi7QqZvQ a8VxNxF80uRWuCVjsLU3WaCLAUnTapHIuQJvInOf0IrcXvC7dKlHhnQt1FhIxUdbDj Qy7qblTn3AnuA== Date: Tue, 28 Jun 2022 02:58:25 +0200 From: "Gustavo A. R. Silva" To: Jason Gunthorpe Cc: Daniel Borkmann , Kees Cook , linux-kernel@vger.kernel.org, x86@kernel.org, dm-devel@redhat.com, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-can@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux1394-devel@lists.sourceforge.net, io-uring@vger.kernel.org, lvs-devel@vger.kernel.org, linux-mtd@lists.infradead.org, kasan-dev@googlegroups.com, linux-mmc@vger.kernel.org, nvdimm@lists.linux.dev, netfilter-devel@vger.kernel.org, coreteam@netfilter.org, linux-perf-users@vger.kernel.org, linux-raid@vger.kernel.org, linux-sctp@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-scsi@vger.kernel.org, target-devel@vger.kernel.org, linux-usb@vger.kernel.org, virtualization@lists.linux-foundation.org, v9fs-developer@lists.sourceforge.net, linux-rdma@vger.kernel.org, alsa-devel@alsa-project.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH][next] treewide: uapi: Replace zero-length arrays with flexible-array members Message-ID: <20220628005825.GA161566@embeddedor> References: <20220627180432.GA136081@embeddedor> <6bc1e94c-ce1d-a074-7d0c-8dbe6ce22637@iogearbox.net> <20220628004052.GM23621@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220628004052.GM23621@ziepe.ca> Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Mon, Jun 27, 2022 at 09:40:52PM -0300, Jason Gunthorpe wrote: > On Mon, Jun 27, 2022 at 08:27:37PM +0200, Daniel Borkmann wrote: > > On 6/27/22 8:04 PM, Gustavo A. R. Silva wrote: > > > There is a regular need in the kernel to provide a way to declare > > > having a dynamically sized set of trailing elements in a structure. > > > Kernel code should always use “flexible array members”[1] for these > > > cases. The older style of one-element or zero-length arrays should > > > no longer be used[2]. > > > > > > This code was transformed with the help of Coccinelle: > > > (linux-5.19-rc2$ spatch --jobs $(getconf _NPROCESSORS_ONLN) --sp-file script.cocci --include-headers --dir . > output.patch) > > > > > > @@ > > > identifier S, member, array; > > > type T1, T2; > > > @@ > > > > > > struct S { > > > ... > > > T1 member; > > > T2 array[ > > > - 0 > > > ]; > > > }; > > > > > > -fstrict-flex-arrays=3 is coming and we need to land these changes > > > to prevent issues like these in the short future: > > > > > > ../fs/minix/dir.c:337:3: warning: 'strcpy' will always overflow; destination buffer has size 0, > > > but the source string has length 2 (including NUL byte) [-Wfortify-source] > > > strcpy(de3->name, "."); > > > ^ > > > > > > Since these are all [0] to [] changes, the risk to UAPI is nearly zero. If > > > this breaks anything, we can use a union with a new member name. > > > > > > [1] https://en.wikipedia.org/wiki/Flexible_array_member > > > [2] https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays > > > > > > Link: https://github.com/KSPP/linux/issues/78 > > > Build-tested-by: https://lore.kernel.org/lkml/62b675ec.wKX6AOZ6cbE71vtF%25lkp@intel.com/ > > > Signed-off-by: Gustavo A. R. Silva > > > --- > > > Hi all! > > > > > > JFYI: I'm adding this to my -next tree. :) > > > > Fyi, this breaks BPF CI: > > > > https://github.com/kernel-patches/bpf/runs/7078719372?check_suite_focus=true > > > > [...] > > progs/map_ptr_kern.c:314:26: error: field 'trie_key' with variable sized type 'struct bpf_lpm_trie_key' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] > > struct bpf_lpm_trie_key trie_key; > > ^ > > This will break the rdma-core userspace as well, with a similar > error: > > /usr/bin/clang-13 -DVERBS_DEBUG -Dibverbs_EXPORTS -Iinclude -I/usr/include/libnl3 -I/usr/include/drm -g -O2 -fdebug-prefix-map=/__w/1/s=. -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -Wmissing-prototypes -Wmissing-declarations -Wwrite-strings -Wformat=2 -Wcast-function-type -Wformat-nonliteral -Wdate-time -Wnested-externs -Wshadow -Wstrict-prototypes -Wold-style-definition -Werror -Wredundant-decls -g -fPIC -std=gnu11 -MD -MT libibverbs/CMakeFiles/ibverbs.dir/cmd_flow.c.o -MF libibverbs/CMakeFiles/ibverbs.dir/cmd_flow.c.o.d -o libibverbs/CMakeFiles/ibverbs.dir/cmd_flow.c.o -c ../libibverbs/cmd_flow.c > In file included from ../libibverbs/cmd_flow.c:33: > In file included from include/infiniband/cmd_write.h:36: > In file included from include/infiniband/cmd_ioctl.h:41: > In file included from include/infiniband/verbs.h:48: > In file included from include/infiniband/verbs_api.h:66: > In file included from include/infiniband/ib_user_ioctl_verbs.h:38: > include/rdma/ib_user_verbs.h:436:34: error: field 'base' with variable sized type 'struct ib_uverbs_create_cq_resp' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] > struct ib_uverbs_create_cq_resp base; > ^ > include/rdma/ib_user_verbs.h:644:34: error: field 'base' with variable sized type 'struct ib_uverbs_create_qp_resp' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] > struct ib_uverbs_create_qp_resp base; > > Which is why I gave up trying to change these.. > > Though maybe we could just switch off -Wgnu-variable-sized-type-not-at-end during configuration ? No. I think now we can easily workaround these sorts of problems with something like this: struct flex { any_type any_member; union { type array[0]; __DECLARE_FLEX_ARRAY(type, array_flex); }; }; and use array_flex in kernel-space. The same for the one-elment arrays in UAPI: struct flex { any_type any_member; union { type array[1]; __DECLARE_FLEX_ARRAY(type, array_flex); }; }; I'll use the idiom above to resolve all these warnings in a follow-up patch. :) Thanks -- Gustavo