Re: CVE-2016-7097 causes acl leak

Mark Salyzyn
2016-12-13T15:56:06Z

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
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);