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Subject: Re: CVE-2016-7097 causes acl leak
To: Cong Wang <xiyou.wangcong@gmail.com>
References: <bb7177d2-08dc-d75c-9012-26e3b2888461@android.com>
 <CAM_iQpX59wQ+ngjLG3WhBXHG5hiHUFDU9SDmz9V2HCGDTRTMXw@mail.gmail.com>
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 <CAM_iQpUp2rFhsu+VZ_FN5RJyTA69mEbqvFju2+0O2VjeLKj5jg@mail.gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>, aneesh.kumar@linux.vnet.ibm.com,
        Jan Kara <jack@suse.cz>, Greg KH <gregkh@linuxfoundation.org>
From: Mark Salyzyn <salyzyn@android.com>
Message-ID: <5c0398cb-9ef2-42f3-0c46-e2e65fe92da9@android.com>
Date: Tue, 13 Dec 2016 15:42:58 -0800
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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.


Sincerely -- Mark Salyzyn