linux-kernel - Re: [PATCH] tracing/syscalls: ignore numbers outside NR

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Date:	Thu, 30 Oct 2014 07:52:23 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Rabin Vincent <rabin@....in>,
	linux-arm-kernel@...ts.infradead.org,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing/syscalls: ignore numbers outside NR_syscalls'
 range

On Thu, 30 Oct 2014 07:10:39 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Thu, 30 Oct 2014 10:18:08 +0000
> Russell King - ARM Linux <linux@....linux.org.uk> wrote:
> 
> > On Thu, Oct 30, 2014 at 01:26:06AM -0700, Christoph Hellwig wrote:
> > > On Wed, Oct 29, 2014 at 11:06:58PM +0100, Rabin Vincent wrote:
> > > > ARM has some private syscalls (for example, set_tls(2)) which lie
> > > > outside the range of NR_syscalls.  If any of these are called while
> > > > syscall tracing is being performed, out-of-bounds array access will
> > > > occur in the ftrace and perf sys_{enter,exit} handlers.
> > > 
> > > While this patch looks like good caution, having syscalls outside of
> > > NR_syscalls seems like a receipe for a disaster.  Can you try to fix
> > > that issue as ell, please?
> > 
> > No.  We've had them since the inception of Linux on ARM.  They predate
> > this tracing crap by more than a decade.  We're not changing them
> > because that would be a massive user API breakage.
> > 
> 
> Since syscall tracing is only broken on ARM, then the fix needs to be
> ARM specific, and not remove the check for all other architectures that
> have a sane NR_syscalls variable.

Bah, I misread the patch. I shouldn't read patches before having my
morning coffee :-/

I read it backwards. I thought it was removing the checks for
NR_syscalls, and not adding them.

I'm fine with the patch as is, and will take it.

But I agree that the syscall tracing code needs a rewrite to handle
these types of issues. It has problems with compat calls as well, which
we simply ignore.

Sorry for the confusion.

-- Steve
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