Date: Sun, 14 Jan 2018 14:34:56 -0800 From: Matthew Wilcox <willy@...radead.org> To: Kees Cook <keescook@...omium.org> Cc: Theodore Ts'o <tytso@....edu>, LKML <linux-kernel@...r.kernel.org>, David Windsor <dave@...lcore.net>, Andreas Dilger <adilger.kernel@...ger.ca>, Ext4 Developers List <linux-ext4@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Alexander Viro <viro@...iv.linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, Andy Lutomirski <luto@...nel.org>, Christoph Hellwig <hch@...radead.org>, Christoph Lameter <cl@...ux.com>, "David S. Miller" <davem@...emloft.net>, Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>, "Martin K. Petersen" <martin.petersen@...cle.com>, Paolo Bonzini <pbonzini@...hat.com>, Christian Borntraeger <borntraeger@...ibm.com>, Christoffer Dall <christoffer.dall@...aro.org>, Dave Kleikamp <dave.kleikamp@...cle.com>, Jan Kara <jack@...e.cz>, Luis de Bethencourt <luisbg@...nel.org>, Marc Zyngier <marc.zyngier@....com>, Rik van Riel <riel@...hat.com>, Matthew Garrett <mjg59@...gle.com>, "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org>, Network Development <netdev@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>, kernel-hardening@...ts.openwall.com Subject: Re: [PATCH 13/38] ext4: Define usercopy region in ext4_inode_cache slab cache 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 <tytso@....edu> 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.
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