linux-kernel - Re: [PATCH v2 10/30] befs: Define usercopy region in befs_inode

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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;
>>>
>>
>>
> 
> 
>