linux-kernel - Re: [RFC][PATCH] exec: Fix use after free of tracepoint trace_sched_process

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Message-ID: <20140204190007.GA8996@redhat.com>
Date:	Tue, 4 Feb 2014 20:00:07 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...IV.linux.org.uk>,
	David Smith <dsmith@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Igor Zhbanov <i.zhbanov@...sung.com>,
	Christoph Hellwig <hch@...radead.org>,
	Paul Menage <menage@...gle.com>
Subject: Re: [RFC][PATCH] exec: Fix use after free of tracepoint
	trace_sched_process_exec

On 02/04, Steven Rostedt wrote:
>
> Now to fix this we need to save the filename before calling
> search_binary_handler(). But we don't want to save it if we are not
> tracing. Why slow everyone else down?

Yes, but it would be much simpler to dup filename unconditionally.

Note also that in this case we can kill linux_binprm->tcomm[] and
simplify filename_to_taskname().

> This works, but is rather ugly.

Yes ;)

> Looking for any other suggestions here.

Perhaps we can change flush_old_exec() to do

	if (!current->mm) {
		bprm->filename = kstrdup(bprm->filename);
		if (bprm->filename)
			bprm->filename_was_dupped = true; // for free_bprm()
		else
			bprm->filename = "//enomem";
	}

This won't penalize the normal exec, and this should fix the problem
afaics.

Perhaps, instead of "//enomem" flush_old_exec() should simply fail,
in this case we can kill bprm->tcomm[] too.

Oleg.

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