Re: [PATCH] printk: fix printk.devkmsg sysctl

[Rabin Vincent]

On Fri, Jan 27, 2017 at 04:01:41PM +0100, Borislav Petkov wrote:
> On Fri, Jan 27, 2017 at 02:11:46PM +0100, Rabin Vincent wrote:
> > @@ -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.

proc_dostring() eats the '\n' and stops after that so we never see it or
what comes after, so we need an strlen():

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