From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Sun, 14 Jan 2018 14:34:56 -0800 From: Matthew Wilcox To: Kees Cook Cc: Theodore Ts'o , 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 Subject: Re: [PATCH 13/38] ext4: Define usercopy region in ext4_inode_cache slab cache Message-ID: <20180114223455.GA32027@bombadil.infradead.org> References: <1515636190-24061-1-git-send-email-keescook@chromium.org> <1515636190-24061-14-git-send-email-keescook@chromium.org> <20180111170119.GB19241@thunk.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: On Thu, Jan 11, 2018 at 03:05:14PM -0800, Kees Cook wrote: > 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. I think Ted was proposing having a per-FS patch that would, say, copy up to 60 bytes to the stack, then memcpy it into the ext4_inode_info. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org