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Date: Mon, 28 Aug 2017 14:57:14 -0700
From: Kees Cook <keescook@...omium.org>
To: "Darrick J. Wong" <darrick.wong@...cle.com>
Cc: LKML <linux-kernel@...r.kernel.org>, David Windsor <dave@...lcore.net>,
linux-xfs@...r.kernel.org, Linux-MM <linux-mm@...ck.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v2 15/30] xfs: Define usercopy region in xfs_inode slab cache
On Mon, Aug 28, 2017 at 2:49 PM, Darrick J. Wong
<darrick.wong@...cle.com> wrote:
> On Mon, Aug 28, 2017 at 02:34:56PM -0700, Kees Cook wrote:
>> From: David Windsor <dave@...lcore.net>
>>
>> The XFS inline inode data, stored in struct xfs_inode_t field
>> i_df.if_u2.if_inline_data and therefore contained in the xfs_inode slab
>> cache, needs to be copied to/from userspace.
>>
>> cache object allocation:
>> fs/xfs/xfs_icache.c:
>> xfs_inode_alloc(...):
>> ...
>> ip = kmem_zone_alloc(xfs_inode_zone, KM_SLEEP);
>>
>> fs/xfs/libxfs/xfs_inode_fork.c:
>> xfs_init_local_fork(...):
>> ...
>> if (mem_size <= sizeof(ifp->if_u2.if_inline_data))
>> ifp->if_u1.if_data = ifp->if_u2.if_inline_data;
>
> Hmm, what happens when mem_size > sizeof(if_inline_data)? A slab object
> will be allocated for ifp->if_u1.if_data which can then be used for
> readlink in the same manner as the example usage trace below. Does
> that allocated object have a need for a usercopy annotation like
> the one we're adding for if_inline_data? Or is that already covered
> elsewhere?
Yeah, the xfs helper kmem_alloc() is used in the other case, which
ultimately boils down to a call to kmalloc(), which is entirely
whitelisted by an earlier patch in the series:
https://lkml.org/lkml/2017/8/28/1026
(It's possible that at some future time we can start segregating
kernel-only kmallocs from usercopy-able kmallocs, but for now, there
are no plans for this.)
-Kees
--
Kees Cook
Pixel Security
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