Commit ce8670ce authored by Eric W. Biederman's avatar Eric W. Biederman Committed by Luis Henriques

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

commit 80dd00a2 upstream.

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.
Reviewed-by: default avatarAndy Lutomirski <luto@amacapital.net>
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent 57d188c3
......@@ -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;
}
}
......
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