Re: CVE-2016-7097 causes acl leak

[Mark Salyzyn]

On 12/12/2016 10:26 PM, Cong Wang wrote:
On Mon, Dec 12, 2016 at 4:26 PM, Mark Salyzyn <saly...@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);