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Date: Thu, 11 Jan 2018 12:01:19 -0500
From: Theodore Ts'o <tytso@....edu>
To: Kees Cook <keescook@...omium.org>
Cc: linux-kernel@...r.kernel.org, David Windsor <dave@...lcore.net>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	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-arch@...r.kernel.org, netdev@...r.kernel.org,
	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 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?

					- Ted

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