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

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Date:   Wed, 14 Dec 2016 15:30:06 -0800
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Mark Salyzyn <salyzyn@...roid.com>
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 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@...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.

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