linux-kernel - Re: [PATCH] printk: Add kernel parameter to disable writes to /dev/kmsg

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Date:	Mon, 25 Apr 2016 14:40:56 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Subject: Re: [PATCH] printk: Add kernel parameter to disable writes to
 /dev/kmsg

On Mon, 25 Apr 2016 20:32:50 +0200
Borislav Petkov <bp@...en8.de> wrote:

> On Mon, Apr 25, 2016 at 01:08:53PM -0400, Steven Rostedt wrote:
> > [ Sorry for the resend, I forgot to add "[PATCH]" to the subject, which
> >   may make this fail filters. ]
> > 
> > Over the weekend my server was acting funny. The display wasn't working
> > well, and I assumed that a driver was going bad. I went to look at the
> > kernel dmesg, but the buffer only had the following over and over:  
> 
> ...
> 
> > +	disable_devkmsg_write
> > +			Disable writing to /dev/kmsg. This prevents user space
> > +			tools from writing into the kernel printk buffers.
> > +			When set, opening /dev/kmsg for write mode will return
> > +			-EPERM.  
> 
> I like the general idea.
> 
> Perhaps can call that param "printk.disable_devkmsg" or so with the
> proper namespace and in light of printk.always_kmsg_dump=...
> 

I agree. And Uwe Kleine-König suggested to make it read_mostly.

I'll send a v2.

-- Steve