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

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Date:   Tue, 13 Dec 2016 07:55:23 -0800
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     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 12/12/2016 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
I chose to modify posix_acl_update_mode as follows and set release_acl 
in the specific drivers, it clears the *acl reference to nul preventing 
posix_acl_release from functioning in these other driver paths:

  */
int posix_acl_update_mode(struct inode *inode, umode_t *mode_p,
               struct posix_acl **acl, ++++bool release_acl)
{
     umode_t mode = inode->i_mode;
     int error;

     error = posix_acl_equiv_mode(*acl, &mode);
     if (error < 0)
         return error;
     if (error == 0) +{
+        if (release_acl)
+            posix_acl_release(*acl);
         *acl = NULL;
+    }
     if (!in_group_p(inode->i_gid) &&
         !capable_wrt_inode_uidgid(inode, CAP_FSETID))
         mode &= ~S_ISGID;
     *mode_p = mode;
     return 0;
}
EXPORT_SYMBOL(posix_acl_update_mode);