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

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Message-ID: <1d564f4f4bec21945a4577fa0d84dc2e.squirrel@webmail.greenhost.nl>
Date:	Fri, 9 Sep 2011 18:22:49 +0200
From:	"Indan Zupancic" <indan@....nu>
To:	"Denys Vlasenko" <dvlasenk@...hat.com>
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, September 9, 2011 14:58, Denys Vlasenko wrote:
> 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 :)

In that case your patch should be allowed to magically propagate
forward in time and change the behavior of future kernels.

Greetings,

Indan


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