linux-kernel - Re: [PATCH 3.10-rc7] Fix: kernel/ptrace.c: ptrace_peek_siginfo() missing __put

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Date:	Sat, 29 Jun 2013 11:29:40 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Andrey Vagin <avagin@...nvz.org>,
	Roland McGrath <roland@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Dave Jones <davej@...hat.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Pedro Alves <palves@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3.10-rc7] Fix: kernel/ptrace.c: ptrace_peek_siginfo()
 missing __put_user() validation

On Fri, Jun 28, 2013 at 6:49 AM, Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
> This __put_user() could be used by unprivileged processes to write into
> kernel memory. The issue here is that even if copy_siginfo_to_user()
> fails, the error code is not checked before __put_user() is executed.
> Luckily, ptrace_peek_siginfo() has been added within the 3.10-rc cycle,
> so it has not hit a stable release yet.

Why do those stupid

    __put_user(info.si_code, &uinfo->si_code))

things exist at all?

As far as I can tell, copy_siginfo_to_user[32]() already copies
si_code. Is the field really so important that it has to be copied
twice, just to make sure the write makes it?

Ok, ok, I see the explanation in the commit message that introduced
this, but it sure as hell isn't obvious from actually looking at the
code. I'm applying the patch, but I think this should have been a
comment in the code as well.

                 Linus
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