Commit 80dd00a2 authored Dec 05, 2014 by Eric W. Biederman

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>

parent be7c6dba

kernel/user_namespace.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -819,7 +819,7 @@ static bool new_idmap_permitted(const struct file *file,
		u32 id = new_map->extent[0].lower_first;
		if (cap_setid == CAP_SETUID) {
		kuid_t uid = make_kuid(ns->parent, id);
		if (uid_eq(uid, file->f_cred->fsuid))
		if (uid_eq(uid, file->f_cred->euid))
		return true;
		}
		}

Admin message