From nobody Thu Nov 21 22:18:38 2024 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 B6B671D1F56; Mon, 18 Nov 2024 18:01:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731952882; cv=none; b=YVDwO8bSVuARxsqT+cMpWeZigXtUky1+ISj3Rb4uxRSZ6CNph/KfakeQ8B5x1ekJt07R3xh3tvzCH+fQ013UO1zmuNk6H/AC76oKgezhUC48io9x5opbqtxm6cnrglJBJYnKAIKE90ffFquN1pVhXV/q8qHGlXRgkZccgZbeqKc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731952882; c=relaxed/simple; bh=zfB93JeM7MiYyZSDcH+Cv62cIp0qVV5wlF6CFxF1K18=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition; b=FlZ2cUBopiXuO1CwhtbGZmU/F5DbL5WPEVqLUfl1tfiI5zQN8yDHCQQKdquCAINL2NVxnLAOrnzF9fnMWFjL30kX3iV8gCMw9d+Vc2Ah3c1+QdSho5//Y+nI4YtU+d3EZs80/tM4oHgIo7JT03T72EYjraFDX8BWy9mL/X16IQ4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ADFMxlH5; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ADFMxlH5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 43352C4CEDB; Mon, 18 Nov 2024 18:01:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1731952882; bh=zfB93JeM7MiYyZSDcH+Cv62cIp0qVV5wlF6CFxF1K18=; h=Date:From:To:Cc:Subject:From; b=ADFMxlH5rEq8MwweLsqJrwre6fEPPlvK7CfR5WASeU6ROG/lDPKs4cDH3pGwbh+L0 2Cxs/HCqT8+pYR3g+KpjUwpu72SIMJRMsCm4mTnczc2KwtZC93Lc3Akrz6bRcw3NBv 1gJtB1Df5vt1jxPkN1YHiWP6QPhdMgOkX2TktPc4n42dqyFVlwZtwD9fixO7UspKF1 h1pTL//ZOUmRluUB6LBq5wS7vDbXIHyMtSlIL+Ew+si0+mYUuAGpVMPfoDdtlG0Ih0 Vc9KchHneimofvsWYT/chcPV8espz8AFrjPSr0xH4sRyrxIW6lxw5ioC/dPiGU/fWo LmpLLNIi/tpwg== Date: Mon, 18 Nov 2024 12:01:17 -0600 From: "Gustavo A. R. Silva" To: Trond Myklebust , Anna Schumaker , Chuck Lever , Jeff Layton , Neil Brown , Olga Kornievskaia , Dai Ngo , Tom Talpey Cc: linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" , linux-hardening@vger.kernel.org Subject: [PATCH][next] fs: nfs: acl: Avoid -Wflex-array-member-not-at-end warning Message-ID: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" -Wflex-array-member-not-at-end was introduced in GCC-14, and we are getting ready to enable it, globally. So, in order to avoid ending up with a flexible-array member in the middle of other structs, we use the `struct_group_tagged()` helper to create a new tagged `struct posix_acl_hdr`. This structure groups together all the members of the flexible `struct posix_acl` except the flexible array. As a result, the array is effectively separated from the rest of the members without modifying the memory layout of the flexible structure. We then change the type of the middle struct member currently causing trouble from `struct posix_acl` to `struct posix_acl_hdr`. We also want to ensure that when new members need to be added to the flexible structure, they are always included within the newly created tagged struct. For this, we use `static_assert()`. This ensures that the memory layout for both the flexible structure and the new tagged struct is the same after any changes. This approach avoids having to implement `struct posix_acl_hdr` as a completely separate structure, thus preventing having to maintain two independent but basically identical structures, closing the door to potential bugs in the future. We also use `container_of()` whenever we need to retrieve a pointer to the flexible structure, through which we can access the flexible-array member, if necessary. So, with these changes, fix the following warning: fs/nfs_common/nfsacl.c:45:26: warning: structure containing a flexible arra= y member is not at the end of another structure [-Wflex-array-member-not-at= -end] Signed-off-by: Gustavo A. R. Silva --- fs/nfs_common/nfsacl.c | 8 +++++--- include/linux/posix_acl.h | 11 ++++++++--- 2 files changed, 13 insertions(+), 6 deletions(-) diff --git a/fs/nfs_common/nfsacl.c b/fs/nfs_common/nfsacl.c index ea382b75b26c..e2eaac14fd8e 100644 --- a/fs/nfs_common/nfsacl.c +++ b/fs/nfs_common/nfsacl.c @@ -42,7 +42,7 @@ struct nfsacl_encode_desc { }; =20 struct nfsacl_simple_acl { - struct posix_acl acl; + struct posix_acl_hdr acl; struct posix_acl_entry ace[4]; }; =20 @@ -112,7 +112,8 @@ int nfsacl_encode(struct xdr_buf *buf, unsigned int bas= e, struct inode *inode, xdr_encode_word(buf, base, entries)) return -EINVAL; if (encode_entries && acl && acl->a_count =3D=3D 3) { - struct posix_acl *acl2 =3D &aclbuf.acl; + struct posix_acl *acl2 =3D + container_of(&aclbuf.acl, struct posix_acl, hdr); =20 /* Avoid the use of posix_acl_alloc(). nfsacl_encode() is * invoked in contexts where a memory allocation failure is @@ -177,7 +178,8 @@ bool nfs_stream_encode_acl(struct xdr_stream *xdr, stru= ct inode *inode, return false; =20 if (encode_entries && acl && acl->a_count =3D=3D 3) { - struct posix_acl *acl2 =3D &aclbuf.acl; + struct posix_acl *acl2 =3D + container_of(&aclbuf.acl, struct posix_acl, hdr); =20 /* Avoid the use of posix_acl_alloc(). nfsacl_encode() is * invoked in contexts where a memory allocation failure is diff --git a/include/linux/posix_acl.h b/include/linux/posix_acl.h index e2d47eb1a7f3..62d497763e25 100644 --- a/include/linux/posix_acl.h +++ b/include/linux/posix_acl.h @@ -27,11 +27,16 @@ struct posix_acl_entry { }; =20 struct posix_acl { - refcount_t a_refcount; - unsigned int a_count; - struct rcu_head a_rcu; + /* New members MUST be added within the struct_group() macro below. */ + struct_group_tagged(posix_acl_hdr, hdr, + refcount_t a_refcount; + unsigned int a_count; + struct rcu_head a_rcu; + ); struct posix_acl_entry a_entries[] __counted_by(a_count); }; +static_assert(offsetof(struct posix_acl, a_entries) =3D=3D sizeof(struct p= osix_acl_hdr), + "struct member likely outside of struct_group_tagged()"); =20 #define FOREACH_ACL_ENTRY(pa, acl, pe) \ for(pa=3D(acl)->a_entries, pe=3Dpa+(acl)->a_count; pa