linux-kernel - Re: [PATCH] kernel/printk/printk.c: check_syslog

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Date:	Thu, 14 May 2015 15:01:54 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Vasily Averin <vvs@...n.com>
Cc:	linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
	Josh Boyer <jwboyer@...hat.com>, Eric Paris <eparis@...hat.com>
Subject: Re: [PATCH] kernel/printk/printk.c: check_syslog_permissions()
 cleanup

On Sun, 10 May 2015 09:35:53 +0300 Vasily Averin <vvs@...n.com> wrote:

> Fixes: 637241a900cb ("kmsg: honor dmesg_restrict sysctl on /dev/kmsg")
> 
> Final version of patch 637241a900cb ("kmsg: honor dmesg_restrict sysctl
> on /dev/kmsg") lost few hooks. As result security_syslog() is not checked
> inside check_syslog_permissions() if dmesg_restrict is set,
> or it can be called twice in do_syslog().

I'm not seeing how security_syslog() is called twice from do_syslog(). 
Put more details in the changelog, please.

> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -484,11 +484,11 @@ int check_syslog_permissions(int type, bool from_file)
>  	 * already done the capabilities checks at open time.
>  	 */
>  	if (from_file && type != SYSLOG_ACTION_OPEN)
> -		return 0;
> +		goto ok;

This seems wrong - we should only call security_syslog() for opens?

>  	if (syslog_action_restricted(type)) {
>  		if (capable(CAP_SYSLOG))
> -			return 0;
> +			goto ok;
>  		/*
>  		 * For historical reasons, accept CAP_SYS_ADMIN too, with
>  		 * a warning.
>
> ...
>
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