linux-kernel - Re: [RFC PATCH] cmdline: Hide "debug" from /proc/cmdline

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Date:	Wed, 2 Apr 2014 15:37:02 -0700
From:	Greg KH <greg@...ah.com>
To:	Mateusz Guzik <mguzik@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
	Ingo Molnar <mingo@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Kay Sievers <kay@...y.org>
Subject: Re: [RFC PATCH] cmdline: Hide "debug" from /proc/cmdline

On Thu, Apr 03, 2014 at 12:12:13AM +0200, Mateusz Guzik wrote:
> On Wed, Apr 02, 2014 at 02:42:19PM -0400, Steven Rostedt wrote:
> > It has come to our attention that a system running a specific user
> > space init program will not boot if you add "debug" to the kernel
> > command line. What happens is that the user space tool parses the
> > kernel command line, and if it sees "debug" it will spit out so much
> > information that the system fails to boot. This basically renders the
> > "debug" option for the kernel useless.
> > 
> > This bug has been reported to the developers of said tool
> > here:
> > 
> >   https://bugs.freedesktop.org/show_bug.cgi?id=76935
> > 
> > The response is:
> > 
> > "Generic terms are generic, not the first user owns them."
> > 
> > That is, the "debug" statement on the *kernel* command line is not
> > owned by the kernel just because it was the first user of it, and
> > they refuse to fix their bug.
> > 
> > Well, my response is, we OWN the kernel command line, and as such, we
> > can keep the users from seeing stuff on it if we so choose. And with
> > that, I propose this patch, which hides "debug" from /proc/cmdline,
> > such that we don't have to worry about tools parsing for it and causing
> > hardship for those trying to debug the kernel.
> > 
> 
> Well, parsing kernel cmdline by systemd is a bad idea, and hiding
> "debug" is even worse. What will happen when the next keyword clashes?
> And how should I check the kernel is booted with "debug"?
> 
> If there is a real need to pass arguments to systemd, how about a
> dedicated option (initargs= or whatever, where it has to be last in
> cmdline), then systemd would be spawned with these arguments and would
> just go over its argv.

Right now it looks like systemd relies on everything with a "systemd."
namespace on the command line, with the exception of "quiet" and
"debug".  I've just submitted a patch to systemd to fix up "debug", and
odds are, "quiet" should be switched as well, but unless anyone runs
into a problem with it, I'll leave that alone for now.

thanks,

greg k-h
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