linux-kernel - Re: [PATCH v2 04/10] ovl: make ioctl() safe

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Message-ID: <e5876ecc-1cce-76d0-528-40b9bc54d0c2@namei.org>
Date:   Tue, 8 Dec 2020 17:57:29 -0800 (PST)
From:   James Morris <jmorris@...ei.org>
To:     Miklos Szeredi <mszeredi@...hat.com>
cc:     "Eric W . Biederman" <ebiederm@...ssion.com>,
        linux-fsdevel@...r.kernel.org, linux-unionfs@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v2 04/10] ovl: make ioctl() safe

On Mon, 7 Dec 2020, Miklos Szeredi wrote:

> ovl_ioctl_set_flags() does a capability check using flags, but then the
> real ioctl double-fetches flags and uses potentially different value.
> 
> The "Check the capability before cred override" comment misleading: user
> can skip this check by presenting benign flags first and then overwriting
> them to non-benign flags.

Is this a security bug which should be fixed in stable?

-- 
James Morris
<jmorris@...ei.org>