linux-kernel - Re: [PATCH 02/27] Add a SysRq option to lift kernel lockdown

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Message-ID: <15833.1551974371@warthog.procyon.org.uk>
Date:   Thu, 07 Mar 2019 15:59:31 +0000
From:   David Howells <dhowells@...hat.com>
To:     Matthew Garrett <matthewgarrett@...gle.com>
Cc:     dhowells@...hat.com, jmorris@...ei.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/27] Add a SysRq option to lift kernel lockdown

Matthew Garrett <matthewgarrett@...gle.com> wrote:

> +		/* Ban synthetic events from some sysrq functionality */
> +		if ((from == SYSRQ_FROM_PROC || from == SYSRQ_FROM_SYNTHETIC) &&
> +		    op_p->enable_mask & SYSRQ_DISABLE_USERSPACE)
> +			printk("This sysrq operation is disabled from userspace.\n");
>  		/*
>  		 * Should we check for enabled operations (/proc/sysrq-trigger
>  		 * should not) and is the invoked operation enabled?
>  		 */
> -		if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
> +		if (from == SYSRQ_FROM_KERNEL || sysrq_on_mask(op_p->enable_mask)) {

There's some missing logic here.  Probably an else is missing, but it seems
more than that.

David