linux-kernel - Re: [PATCH] serial: core: fix suspicious security_locked

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Message-ID: <YJUyJcNT9RDaJc4P@kroah.com>
Date:   Fri, 7 May 2021 14:27:17 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Ondrej Mosnacek <omosnace@...hat.com>
Cc:     linux-serial@...r.kernel.org, David Howells <dhowells@...hat.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Jiri Slaby <jirislaby@...nel.org>, selinux@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        James Morris <jmorris@...ei.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: core: fix suspicious security_locked_down() call

On Fri, May 07, 2021 at 01:57:19PM +0200, Ondrej Mosnacek wrote:
> The commit that added this check did so in a very strange way - first
> security_locked_down() is called, its value stored into retval, and if
> it's nonzero, then an additional check is made for (change_irq ||
> change_port), and if this is true, the function returns. However, if
> the goto exit branch is not taken, the code keeps the retval value and
> continues executing the function. Then, depending on whether
> uport->ops->verify_port is set, the retval value may or may not be reset
> to zero and eventually the error value from security_locked_down() may
> abort the function a few lines below.
> 
> I will go out on a limb and assume that this isn't the intended behavior
> and that an error value from security_locked_down() was supposed to
> abort the function only in case (change_irq || change_port) is true.

Are you _sure_ about this?

Verification from the authors and users of this odd feature might be
good to have, as I am loath to change how this works without them
weighing in here.

thanks,

greg k-h