Re: CVE-2016-7097 causes acl leak

Mark Salyzyn
2016-12-15T15:22:34Z

On 12/14/2016 03:30 PM, Greg KH wrote:
> On Wed, Dec 14, 2016 at 12:20:50PM -0800, Mark Salyzyn wrote:
>> 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@android.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.
> Did I take the fix in 3.10-stable? What was the git commit id? Is 3.10
> "broken" in this way? Is any other stable kernel broken?
>
> I still don't have any idea of what is going on here...
>
> greg k-h

Nothing is going on here, it is a heads up, eventually CVE's get
backported to stable as we do take them in through those paths. Telling
you to be aware that the original commit causes a leak, and my
experience has found that the leak affects these four file system drivers.

-- Mark