tree 40ff3ad2233bc6f08bcde250acc87a29af9ad0af
parent be7c6dba2332cef0677fbabb606e279ae76652c3
author Eric W. Biederman <ebiederm@xmission.com> 1417825590 -0600
committer Eric W. Biederman <ebiederm@xmission.com> 1418166512 -0600

userns: Check euid no fsuid when establishing an unprivileged uid mapping

setresuid allows the euid to be set to any of uid, euid, suid, and
fsuid.  Therefor it is safe to allow an unprivileged user to map
their euid and use CAP_SETUID privileged with exactly that uid,
as no new credentials can be obtained.

I can not find a combination of existing system calls that allows setting
uid, euid, suid, and fsuid from the fsuid making the previous use
of fsuid for allowing unprivileged mappings a bug.

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

Cc: stable@vger.kernel.org
Reviewed-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>