linux-kernel - Re: [PATCH 1/2] ptrace: don't modify flags on PTRACE

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Date:	Fri, 09 Sep 2011 14:58:02 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Indan Zupancic <indan@....nu>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/2] ptrace: don't modify flags on PTRACE_SETOPTIONS
 failure

On Fri, 2011-09-09 at 14:44 +0200, Indan Zupancic wrote:
> Hello,
> 
> On Fri, September 9, 2011 08:24, Denys Vlasenko wrote:
> > It's very unlikely that there is userspace code in the wild which
> > will be affected by this change: it should have the form
> >
> >     ptrace(PTRACE_SETOPTIONS, pid, 0, PTRACE_O_BOGUSOPT)
> >
> > where PTRACE_O_BOGUSOPT is a constant unknown to the kernel.
> > But kernel headers, naturally, don't contain any
> > PTRACE_O_BOGUSOPTs, thus the only way userspace can use one
> > if it defines one itself. I can't see why anyone would do such
> > a thing deliberately.
> 
> The only realistic case is when a program compiled on a newer
> kernel is run on an older kernel, when it does things like
> 
> #ifndef PTRACE_O_TRACEFORK
> 	opts |= PTRACE_O_TRACEFORK;
> #endif
> 
> and happened to work on older kernels because it didn't check
> the return value.

Well, older kernels, of course, will have *old* behavior
of SETOPTIONS too! My patch will not magically propagate
back in time and change behavior of old kernels :)

-- 
vda


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