Re: CVE-2016-7097 causes acl leak

Mark Salyzyn
2016-12-14T20:20:54Z

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.

-- Mark