linux-kernel - Re: [PATCH v3 1/3] x86/ptrace: Stop setting TS

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Date:	Mon, 25 Jul 2016 09:57:36 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Pedro Alves <palves@...hat.com>, Oleg Nesterov <oleg@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	Borislav Petkov <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>
Subject: Re: [PATCH v3 1/3] x86/ptrace: Stop setting TS_COMPAT in ptrace code

On Jul 24, 2016 11:38 PM, "Ingo Molnar" <mingo@...nel.org> wrote:
>
>
> * Andy Lutomirski <luto@...capital.net> wrote:
>
> > On Mon, Jun 20, 2016 at 4:39 PM, Andy Lutomirski <luto@...nel.org> wrote:
> > > Setting TS_COMPAT in ptrace is wrong: if we happen to do it during
> > > syscall entry, then we'll confuse seccomp and audit.  (The former
> > > isn't a security problem: seccomp is currently entirely insecure if a
> > > malicious ptracer is attached.)  As a minimal fix, this patch adds a
> > > new flag TS_I386_REGS_POKED that handles the ptrace special case.
> >
> > Hi Ingo-
> >
> > Could you apply this one patch for 4.8?  While I don't think it's a
> > significant security issue in 4.7 or earlier, leaving it unfixed in
> > 4.8 will introduce a potentially unpleasant interaction with some
> > seccomp changes that are queued up in the
> > security tree for 4.8.
> >
> > It will have a trivially-resolvable conflict with -mm.
> >
> > The rest of the series this is in can wait.
>
> I don't mind the rest of the series either - could you please repost it (with the
> review feedback addressed)?

I'm nervous about it for a couple reasons involving the fact that it's
user visible.

1. It doesn't make gdb work right in all the cases that gdb currently
gets wrong.  I haven't had time to think about whether there's a
minimal tweak that would fix this.

2. It might have annoying interactions with seccomp whitelists.  I
don't know that for sure, but I still don't love it.


Patch 1 is only user-visible in the case where the current behavior is
clearly wrong, so I'd personally be more comfortable applying just
patch 1 for 4.8.

--Andy