Re: CVE request -- linux kernel: Setting a POSIX ACL via setxattr doesn't clear the setgid bit

[Vladis Dronov <vdronov () redhat com>]

Hello,
 
Honestly, I do not see a relation between this patch and overlays. The patch
touches the code of underlying filesystems. So, most probably, upperdir ACL
issue is not fixed by this suggested patch.

Best regards,
Vladis Dronov | Red Hat, Inc. | Product Security Engineer


----- Original Message -----
From: me () halfdog net
To: oss-security () lists openwall com, "Vladis Dronov" <vdronov () redhat com>
Sent: Saturday, August 27, 2016 1:24:47 PM
Subject: Re: [oss-security] CVE request -- linux kernel: Setting a POSIX ACL via setxattr doesn't clear the setgid bit

Vladis Dronov writes:
> Hello,
>
> We would like to ask for a CVE-ID for the following securuty flaw.
>
> When file permissions are modified via chmod(2) and the user is not in
> the owning group or capable of CAP_FSETID, the setgid bit is cleared in
> inode_change_ok().  Setting a POSIX ACL via setxattr(2) sets the file
> permissions as well as the new ACL, but doesn't clear the setgid bit in
> a similar way; this allows to bypass the check in chmod(2).
> ...

Does this also fix the upperdir ACL access gain from
http://www.halfdog.net/Security/2016/UserNamespaceOverlayfsXattrSetgidPrivilegeEscalation/
?

The overlayfs upperdir part is already fixed, so the one would
have to execute replacement commands for the steps already prohibited
by the userns/overlayfs fixes.

hd