From mboxrd@z Thu Jan 1 00:00:00 1970 MIME-Version: 1.0 Sender: keescook@google.com In-Reply-To: <20180111170119.GB19241@thunk.org> References: <1515636190-24061-1-git-send-email-keescook@chromium.org> <1515636190-24061-14-git-send-email-keescook@chromium.org> <20180111170119.GB19241@thunk.org> From: Kees Cook Date: Thu, 11 Jan 2018 15:05:14 -0800 Message-ID: Content-Type: text/plain; charset="UTF-8" Subject: [kernel-hardening] Re: [PATCH 13/38] ext4: Define usercopy region in ext4_inode_cache slab cache To: Theodore Ts'o , Kees Cook , LKML , David Windsor , Andreas Dilger , Ext4 Developers List , Linus Torvalds , Alexander Viro , Andrew Morton , Andy Lutomirski , Christoph Hellwig , Christoph Lameter , "David S. Miller" , Laura Abbott , Mark Rutland , "Martin K. Petersen" , Paolo Bonzini , Christian Borntraeger , Christoffer Dall , Dave Kleikamp , Jan Kara , Luis de Bethencourt , Marc Zyngier , Rik van Riel , Matthew Garrett , "linux-fsdevel@vger.kernel.org" , linux-arch , Network Development , Linux-MM , kernel-hardening@lists.openwall.com List-ID: On Thu, Jan 11, 2018 at 9:01 AM, Theodore Ts'o wrote: > On Wed, Jan 10, 2018 at 06:02:45PM -0800, Kees Cook wrote: >> The ext4 symlink pathnames, stored in struct ext4_inode_info.i_data >> and therefore contained in the ext4_inode_cache slab cache, need >> to be copied to/from userspace. > > Symlink operations to/from userspace aren't common or in the hot path, > and when they are in i_data, limited to at most 60 bytes. Is it worth > it to copy through a bounce buffer so as to disallow any usercopies > into struct ext4_inode_info? If this is the only place it's exposed, yeah, that might be a way to avoid the per-FS patches. This would, AIUI, require changing readlink_copy() to include a bounce buffer, and that would require an allocation. I kind of prefer just leaving the per-FS whitelists, as then there's no global overhead added. -Kees -- Kees Cook Pixel Security