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Message-ID: <6a2eb4e1-1654-5025-4edd-dd3faf978aad@kernel.org>
Date: Tue, 29 Aug 2017 18:10:14 +0100
From: Luis de Bethencourt <luisbg@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: LKML <linux-kernel@...r.kernel.org>, David Windsor <dave@...lcore.net>,
Salah Triki <salah.triki@...il.com>, Linux-MM <linux-mm@...ck.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v2 10/30] befs: Define usercopy region in befs_inode_cache
slab cache
On 08/29/2017 04:36 PM, Kees Cook wrote:
> On Tue, Aug 29, 2017 at 3:12 AM, Luis de Bethencourt <luisbg@...nel.org> wrote:
>> Hello Kees,
>>
>> This is great. Thanks :)
>>
>> Will merge into my befs tree.
>
> Hi! Actually, this depends on the rest of the series, which should be
> merged together. If you can Ack this, I'll include it in my usercopy
> tree.
>
> Thanks!
>
> -Kees
>
Sure!
Acked-by: Luis de Bethencourt <luisbg@...nel.org>
>>
>> Luis
>>
>>
>> On 08/28/2017 10:34 PM, Kees Cook wrote:
>>>
>>> From: David Windsor <dave@...lcore.net>
>>>
>>> befs symlink pathnames, stored in struct befs_inode_info.i_data.symlink
>>> and therefore contained in the befs_inode_cache slab cache, need to be
>>> copied to/from userspace.
>>>
>>> cache object allocation:
>>> fs/befs/linuxvfs.c:
>>> befs_alloc_inode(...):
>>> ...
>>> bi = kmem_cache_alloc(befs_inode_cachep, GFP_KERNEL);
>>> ...
>>> return &bi->vfs_inode;
>>>
>>> befs_iget(...):
>>> ...
>>> strlcpy(befs_ino->i_data.symlink, raw_inode->data.symlink,
>>> BEFS_SYMLINK_LEN);
>>> ...
>>> inode->i_link = befs_ino->i_data.symlink;
>>>
>>> example usage trace:
>>> readlink_copy+0x43/0x70
>>> vfs_readlink+0x62/0x110
>>> SyS_readlinkat+0x100/0x130
>>>
>>> fs/namei.c:
>>> readlink_copy(..., link):
>>> ...
>>> copy_to_user(..., link, len);
>>>
>>> (inlined in vfs_readlink)
>>> generic_readlink(dentry, ...):
>>> struct inode *inode = d_inode(dentry);
>>> const char *link = inode->i_link;
>>> ...
>>> readlink_copy(..., link);
>>>
>>> In support of usercopy hardening, this patch defines a region in the
>>> befs_inode_cache slab cache in which userspace copy operations are
>>> allowed.
>>>
>>> This region is known as the slab cache's usercopy region. Slab caches can
>>> now check that each copy operation involving cache-managed memory falls
>>> entirely within the slab's usercopy region.
>>>
>>> This patch is modified from Brad Spengler/PaX Team's PAX_USERCOPY
>>> whitelisting code in the last public patch of grsecurity/PaX based on my
>>> understanding of the code. Changes or omissions from the original code are
>>> mine and don't reflect the original grsecurity/PaX code.
>>>
>>> Signed-off-by: David Windsor <dave@...lcore.net>
>>> [kees: adjust commit log, provide usage trace]
>>> Cc: Luis de Bethencourt <luisbg@...nel.org>
>>> Cc: Salah Triki <salah.triki@...il.com>
>>> Signed-off-by: Kees Cook <keescook@...omium.org>
>>> ---
>>> fs/befs/linuxvfs.c | 14 +++++++++-----
>>> 1 file changed, 9 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/fs/befs/linuxvfs.c b/fs/befs/linuxvfs.c
>>> index 4a4a5a366158..1c2dcbee79dd 100644
>>> --- a/fs/befs/linuxvfs.c
>>> +++ b/fs/befs/linuxvfs.c
>>> @@ -444,11 +444,15 @@ static struct inode *befs_iget(struct super_block
>>> *sb, unsigned long ino)
>>> static int __init
>>> befs_init_inodecache(void)
>>> {
>>> - befs_inode_cachep = kmem_cache_create("befs_inode_cache",
>>> - sizeof (struct
>>> befs_inode_info),
>>> - 0, (SLAB_RECLAIM_ACCOUNT|
>>> -
>>> SLAB_MEM_SPREAD|SLAB_ACCOUNT),
>>> - init_once);
>>> + befs_inode_cachep = kmem_cache_create_usercopy("befs_inode_cache",
>>> + sizeof(struct befs_inode_info), 0,
>>> + (SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD|
>>> + SLAB_ACCOUNT),
>>> + offsetof(struct befs_inode_info,
>>> + i_data.symlink),
>>> + sizeof_field(struct befs_inode_info,
>>> + i_data.symlink),
>>> + init_once);
>>> if (befs_inode_cachep == NULL)
>>> return -ENOMEM;
>>>
>>
>>
>
>
>
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