linux-kernel - Re: CVE-2016-7097 causes acl leak

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Message-ID: <3db72683-e810-38f8-87c8-dc7fa6a50aa6@android.com>
Date:   Wed, 14 Dec 2016 12:20:50 -0800
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        aneesh.kumar@...ux.vnet.ibm.com, Jan Kara <jack@...e.cz>
Subject: Re: CVE-2016-7097 causes acl leak

On 12/13/2016 04:00 PM, Greg KH wrote:
> On Tue, Dec 13, 2016 at 03:42:58PM -0800, Mark Salyzyn wrote:
>> On 12/12/2016 10:26 PM, Cong Wang wrote:
>>> On Mon, Dec 12, 2016 at 4:26 PM, Mark Salyzyn <salyzyn@...roid.com> wrote:
>>>> The leaks were introduced in 9p, gfs2, jfs and xfs drivers only.
>>> Only the 9p case is obvious to me:
>>>
>>> diff --git a/fs/9p/acl.c b/fs/9p/acl.c
>>> index b3c2cc7..082d227 100644
>>> --- a/fs/9p/acl.c
>>> +++ b/fs/9p/acl.c
>>> @@ -277,6 +277,7 @@ static int v9fs_xattr_set_acl(const struct
>>> xattr_handler *handler,
>>>           case ACL_TYPE_ACCESS:
>>>                   if (acl) {
>>>                           struct iattr iattr;
>>> +                       struct posix_acl *old_acl = acl;
>>>
>>>                           retval = posix_acl_update_mode(inode,
>>> &iattr.ia_mode, &acl);
>>>                           if (retval)
>>> @@ -287,6 +288,7 @@ static int v9fs_xattr_set_acl(const struct
>>> xattr_handler *handler,
>>>                                    * by the mode bits. So don't
>>>                                    * update ACL.
>>>                                    */
>>> +                               posix_acl_release(old_acl);
>>>                                   value = NULL;
>>>                                   size = 0;
>>>                           }
>>>
>>>
>>> The rest are anti-pattern (modifying parameters on stack via address)
>>> but look correct.
>> Greg KH: Beware that this similar fix needs to be applied to _backports_ to
>> stable kernel trees on other filesystem driver that have the same pattern
>> (with local posix_acl_release(acl) calls). I have found that depending on
>> vintage these would include this driver 9p, and possibly gfs2, jfs and xfs.
>> Be aware.
> I don't understand what you mean here.  What needs to be "backported" to
> the stable tree?  What commit in Linus's tree do I pick?  If not a
> commit there, where is it?
>
> totally confused,
>
> greg k-h

In 3.10-stable if you took the original CVE-2016-7097 fix it could break 
four file system drivers, the fix for each would 'look like' this one 
fix for the 9p driver.

-- Mark