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Date: Thu, 11 Jan 2018 12:01:19 -0500
From: Theodore Ts'o <tytso@mit.edu>
Subject: Re: [PATCH 13/38] ext4: Define usercopy region in ext4_inode_cache
 slab cache
Message-ID: <20180111170119.GB19241@thunk.org>
References: <1515636190-24061-1-git-send-email-keescook@chromium.org>
 <1515636190-24061-14-git-send-email-keescook@chromium.org>
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In-Reply-To: <1515636190-24061-14-git-send-email-keescook@chromium.org>
Sender: owner-linux-mm@kvack.org
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To: Kees Cook <keescook@chromium.org>
Cc: linux-kernel@vger.kernel.org, David Windsor <dave@nullcore.net>, Andreas Dilger <adilger.kernel@dilger.ca>, linux-ext4@vger.kernel.org, Linus Torvalds <torvalds@linux-foundation.org>, Alexander Viro <viro@zeniv.linux.org.uk>, Andrew Morton <akpm@linux-foundation.org>, Andy Lutomirski <luto@kernel.org>, Christoph Hellwig <hch@infradead.org>, Christoph Lameter <cl@linux.com>, "David S. Miller" <davem@davemloft.net>, Laura Abbott <labbott@redhat.com>, Mark Rutland <mark.rutland@arm.com>, "Martin K. Petersen" <martin.petersen@oracle.com>, Paolo Bonzini <pbonzini@redhat.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Christoffer Dall <christoffer.dall@linaro.org>, Dave Kleikamp <dave.kleikamp@oracle.com>, Jan Kara <jack@suse.cz>, Luis de Bethencourt <luisbg@kernel.org>, Marc Zyngier <marc.zyngier@arm.com>, Rik van Riel <riel@redhat.com>, Matthew Garrett <mjg59@google.com>, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, netdev@vger.kernel.org, linux-mm@kvack.org, kernel-hardening@lists.openwall.com

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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