[PATCH 3.14 37/52] userns: Dont allow unprivileged creation of gid mappings

From: Greg Kroah-Hartman
Date: Tue Jan 06 2015 - 21:10:48 EST


3.14-stable review patch. If anyone has any objections, please let me know.

------------------

From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>

commit be7c6dba2332cef0677fbabb606e279ae76652c3 upstream.

As any gid mapping will allow and must allow for backwards
compatibility dropping groups don't allow any gid mappings to be
established without CAP_SETGID in the parent user namespace.

For a small class of applications this change breaks userspace
and removes useful functionality. This small class of applications
includes tools/testing/selftests/mount/unprivilged-remount-test.c

Most of the removed functionality will be added back with the addition
of a one way knob to disable setgroups. Once setgroups is disabled
setting the gid_map becomes as safe as setting the uid_map.

For more common applications that set the uid_map and the gid_map
with privilege this change will have no affect.

This is part of a fix for CVE-2014-8989.

Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
kernel/user_namespace.c | 5 -----
1 file changed, 5 deletions(-)

--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -814,11 +814,6 @@ static bool new_idmap_permitted(const st
if (uid_eq(uid, file->f_cred->fsuid))
return true;
}
- else if (cap_setid == CAP_SETGID) {
- kgid_t gid = make_kgid(ns->parent, id);
- if (gid_eq(gid, file->f_cred->fsgid))
- return true;
- }
}

/* Allow anyone to set a mapping that doesn't require privilege */


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/