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 3B413C0015E for ; Thu, 13 Jul 2023 05:44:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232495AbjGMFoy (ORCPT ); Thu, 13 Jul 2023 01:44:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33322 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232641AbjGMFox (ORCPT ); Thu, 13 Jul 2023 01:44:53 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 868451989; Wed, 12 Jul 2023 22:44:52 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 23B4761A24; Thu, 13 Jul 2023 05:44:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7361CC433C8; Thu, 13 Jul 2023 05:44:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1689227091; bh=6XCJ3zXa9Yfor+KTu4kClEjr5YTvx3XG0W6PUIBvJgw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=XTVmWzDPSv1Nkby5x97GOJHvh7hc11w1GC1heEkW/FEgs3OTB+N2jp6Da/D1rAclD l+vOzUHModm+y+JXOKWuSelpyC5D+b4PTvFoKOsqug9u3eN/K0J9jRdAEhqc9dMDYV /gg/fuTv7Rs4oxdX27ZOC6XzxIb0wVTVnTTpHJ48A7hHwPPGbmSZ6SnHoJFQxBDe9a K15fzypJaKzu5NbY4cEmB5uYqFjs2Ed0LSlavD/+bHOwMqJNDj+LhPl/Xk82zn93Vu R0ViGF6fI3czvdmGc3Ad7YMLteN7qQWMJdv/HkSldPKBXIoR0fPYReWWGK6joR/hH8 x20Cp+yaPAFGw== Date: Wed, 12 Jul 2023 22:44:50 -0700 From: "Darrick J. Wong" To: Christoph Hellwig Cc: Kees Cook , Carlos Maiolino , Dave Chinner , Jeff Layton , Eric Biggers , "Gustavo A. R. Silva" , linux-xfs@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH] libxfs: Redefine 1-element arrays as flexible arrays Message-ID: <20230713054450.GQ108251@frogsfrogsfrogs> References: <20230711222025.never.220-kees@kernel.org> <20230712053738.GD108251@frogsfrogsfrogs> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org On Wed, Jul 12, 2023 at 06:09:31AM -0700, Christoph Hellwig wrote: > On Tue, Jul 11, 2023 at 10:37:38PM -0700, Darrick J. Wong wrote: > > Here's my version, where I go for a straight a[1] -> a[] conversion and > > let downstream attrlist ioctl users eat their lumps. What do you think > > of the excess-documentation approach? > > I think this is roughtly the right thing, with one big caveat: > > > + /* In Linux 6.5 this flex array was changed from list[1] to list[]. */ > > For all the format headers there's no need for these comments. We've > done this for various other structures that had the old one size arrays > and never bothered. Dave looked at an earlier version and wanted the comments for xfs_da_format.h to steer people at the entsize helpers. I more or less agree that it's overkill everywhere else though. > > diff --git a/libxfs/xfs_fs.h b/libxfs/xfs_fs.h > > index 9c60ebb3..8927ecb2 100644 > > --- a/libxfs/xfs_fs.h > > +++ b/libxfs/xfs_fs.h > > @@ -588,16 +588,19 @@ typedef struct xfs_attrlist_cursor { > > * > > * NOTE: struct xfs_attrlist must match struct attrlist defined in libattr, and > > * struct xfs_attrlist_ent must match struct attrlist_ent defined in libattr. > > + * > > + * WARNING: In Linux 6.5, al_offset and a_name were changed from array[1] to > > + * array[]. Anyone using sizeof is (already) broken! > > */ > > struct xfs_attrlist { > > __s32 al_count; /* number of entries in attrlist */ > > __s32 al_more; /* T/F: more attrs (do call again) */ > > - __s32 al_offset[1]; /* byte offsets of attrs [var-sized] */ > > + __s32 al_offset[]; /* byte offsets of attrs [var-sized] */ > > }; > > > > struct xfs_attrlist_ent { /* data from attr_list() */ > > __u32 a_valuelen; /* number bytes in value of attr */ > > - char a_name[1]; /* attr name (NULL terminated) */ > > + char a_name[]; /* attr name (NULL terminated) */ > > }; > > Now these are currently exposed in a xfsprogs headeer and IFF someone > is using them it would break them in nasty ways. That being said, > xfsprogs itself doesn't use them as it relies on identically layed > out but differntly named structures from libattr. > > So I think we should just move these two out of xfs_fs.h, because > while they document a UAPI, they aren't actually used by userspace. > > With that the need for any caution goes away and we can just fix the > definition without any caveats. So I looked at the libattr headers for Ubuntu 22.04 and saw this: /* * List the names and sizes of the values of all the attributes of an object. * "Cursor" must be allocated and zeroed before the first call, it is used * to maintain context between system calls if all the attribute names won't * fit into the buffer on the first system call. * The return value is -1 on error (w/errno set appropriately), 0 on success. */ extern int attr_list(const char *__path, char *__buffer, const int __buffersize, int __flags, attrlist_cursor_t *__cursor) __attribute__ ((deprecated ("Use listxattr or llistxattr instead"))); extern int attr_listf(int __fd, char *__buffer, const int __buffersize, int __flags, attrlist_cursor_t *__cursor) __attribute__ ((deprecated ("Use flistxattr instead"))); I take that as a sign that they could drop all these xfs-specific APIs one day, which means we ought to keep them in xfs_fs.h. --D