linux-kernel - Re: FTRACE_WARN_ON((rec->flags & ~FTRACE_FL

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Date:	Thu, 30 Jan 2014 08:55:33 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Dave Jones <davej@...hat.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: FTRACE_WARN_ON((rec->flags & ~FTRACE_FL_MASK) == 0))

On Thu, 30 Jan 2014 00:32:32 -0500
Dave Jones <davej@...hat.com> wrote:

> On Wed, Jan 29, 2014 at 11:50:43PM -0500, Steven Rostedt wrote:
>  > Are you running as root?  If not, you found another way to get perf to start function tracing.
> 
> Good point. In this case, I was trying some new experimental trinity code
> that starts as root, generates fd's, then drops privs before doing syscalls.
> 
> So the "generate fds" part did some perf_event_open's as root, yeah.
> 
> While that's less scary from a security pov than it was last time, it's still
> something that aparently needs fixing.
> 

OK, then I'm not as worried (phew!). But you are correct, this needs to
be fixed. How do I run just perf commands from trinity? I do not think
this occurs from any other systemcall needing to be run.

Peter, Jiri,

Although we fixed the bug that let a normal user enable function
tracing from perf, we never figured out why perf screws up the function
tracing filter accounting. That will happen if you either use a
uninitialized ftrace hash, or modify the hash without using the ftrace
API. If it is the latter, it is probably done by some kind of use after
free.

-- Steve
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