linux-kernel - Re: [PATCH] printk: fix printk.devkmsg sysctl

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Date:   Fri, 27 Jan 2017 16:01:41 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Rabin Vincent <rabin.vincent@...s.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        Rabin Vincent <rabinv@...s.com>
Subject: Re: [PATCH] printk: fix printk.devkmsg sysctl

On Fri, Jan 27, 2017 at 02:11:46PM +0100, Rabin Vincent wrote:
> From: Rabin Vincent <rabinv@...s.com>
> 
> The comment says that it doesn't want to accept trailing crap but that's
> just what it allows:

...

> @@ -177,7 +177,7 @@ int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write,
>  		 * Do not accept an unknown string OR a known string with
>  		 * trailing crap...
>  		 */
> -		if (err < 0 || (err + 1 != *lenp)) {

Grr, that's that damn '\n'

echo off > /proc/sys/kernel/printk_devkmsg

works, of course.

Ok, I don't want to relax the strncmp() above and would still like to
return the exact length compared.

So please change the check above to allow the following inputs:

	<str>

or

	<str>\n

I.e., a trailing, *optional*, '\n' is allowed.

This way we're accepting the two most common ways to input strings:

$ echo <str> > ...

and 

$ echo -n <str> > ...

Thanks!

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--