From mboxrd@z Thu Jan 1 00:00:00 1970 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 39F8115198D; Wed, 5 Feb 2025 14:11:10 +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=1738764670; cv=none; b=BMqXZE71pYjsh0U1dnnhG/nxnrR0vF/Kj/8EempbL74chx8jQUZMlduq72/A3lNxLai/uEmEmfSXoxWnbFR1PI7TXvlQnvdQOtDXkjHyfrUxCtfct1lWwL2podSqNXgC4jqFyL9AbQnSzwv1eyjlDVbBFXaqyFGe/pwXJ5z9JiE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738764670; c=relaxed/simple; bh=MkBrW83E83JxBCXrhFthWYfVkvOxdS1yoeVlbf0Rmpo=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=Mn9lKkjspW0W3OJ5OphQQKlTuIyvAkpe4OwKvIa8uWtVf0yJ7srWmHvN3niGEq8ugF9ME3C3P5+5W/MPBkVS1lPLYTF1BcTqoJRCmBnOMn6imZAhyLyWYe2qTC67NtE/kOezO8LPJZzIHVLJAfcp4eaCBefY8uvUN5uYGCOQpMU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=uzrnztJ6; 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="uzrnztJ6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 150FCC4CED1; Wed, 5 Feb 2025 14:11:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1738764670; bh=MkBrW83E83JxBCXrhFthWYfVkvOxdS1yoeVlbf0Rmpo=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=uzrnztJ6wVL4IFcAqlwATtZc1rxSoYPwnpX42GwlzzaYWInOXGiNCyKBQsbftt0In hvdhUFhgBb8rZutvamDxr9Xx6d+c8FXi6tEaqQZGeAvQRCmyKXJ1XqFuCFxMD2XJlJ TG/qWiL/wtQkkBnI4mt/kOCWJpq4HazDpdOJXK5/fRjmhdtyoMKnV1FFbz3Q4vg0mb EclE5jlfD5KYm6Fdo9vlExlx9iSegZ/jRVA6UFPeWCfWBTowo4V6OEvcDLTbYNg8BN ngedUOcIiGF9RACnYdaNPC4PWaJmvV2YiK6L7T2o7lEyct30nCMOO1qZuB+Nt6um/c 6xD+AFC5DCiDw== Message-ID: <2f98596d5403080ac3d2757482207d84ce1502a9.camel@kernel.org> Subject: Re: [RESEND PATCH][next] fs: nfs: acl: Avoid -Wflex-array-member-not-at-end warning From: Jeff Layton To: "Gustavo A. R. Silva" , Chuck Lever , Neil Brown , Olga Kornievskaia , Dai Ngo , Tom Talpey , Trond Myklebust , Anna Schumaker Cc: linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Date: Wed, 05 Feb 2025 09:11:08 -0500 In-Reply-To: References: Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn VluJH0/RcxEeFbnSaswVChNSGa7mXJrTR22lRL6ZPjdMgS2Km90haWPRc8Wolcz07Y2se0xpGVLEQ cDEsvv5IMmeMe1/qLZ6NaVkNuL3WOXvxaVT9USW1+/SGipO2IpKJjeDZfehlB/kpfF24+RrK+seQf 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Yy9YbXtWctUz8uvDR7shsQxAhX3qO7DilMtuGo1v97I/Kx4gXQ52syh/w6EBny71CZrOgD6kJwPVV AaM1LRC28muq91WCFhs/nzHozpbzcheyGtMUI2Ao4K6mnY+3zIuXPygZMFr9KXE6fF7HzKxKuZMJO aEZCiDOq0anx6FmOzs5E6Jqdpo/mtI8beK+BE7Va6ni7YrQlnT0i3vaTVMTiCThbqsB20VrbMjlhp f8lfK1XVNbRq/R7GZ9zHESlsa35ha60yd/j3pu5hT2xyy8krV8vGhHvnJ1XRMJBAB/UYb6FyC7S+m QZIQXVeAA+smfTT0tDrisj1U5x6ZB9b3nBg65kc= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.3 (3.54.3-1.fc41) Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2025-02-04 at 13:33 +1030, Gustavo A. R. Silva wrote: > -Wflex-array-member-not-at-end was introduced in GCC-14, and we are > getting ready to enable it, globally. >=20 > 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. >=20 > 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`. >=20 > 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. >=20 > 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. >=20 > 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. >=20 > So, with these changes, fix the following warning: >=20 > fs/nfs_common/nfsacl.c:45:26: warning: structure containing a flexible ar= ray member is not at the end of another structure [-Wflex-array-member-not-= at-end] >=20 > 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(-) >=20 > 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 b= ase, 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, st= ruct 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= posix_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