Re: CVE-2016-7097 causes acl leak

From: Mark Salyzyn
Date: Tue Dec 13 2016 - 18:44:06 EST

On 12/12/2016 10:26 PM, Cong Wang wrote:
On Mon, Dec 12, 2016 at 4:26 PM, Mark Salyzyn <salyzyn@xxxxxxxxxxx> 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,
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