netdev - Re: [EXAMPLE CODE] Parasite thread injection and TCP connection hijacking

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Date:	Sat, 6 Aug 2011 09:15:45 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	Tejun Heo <tj@...nel.org>
Cc:	Matt Helsley <matthltc@...ibm.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Nathan Lynch <ntl@...ox.com>,
	Oren Laadan <orenl@...columbia.edu>,
	Daniel Lezcano <dlezcano@...ibm.com>, S@....edu,
	"James E.J. Bottomley" <JBottomley@...allels.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [EXAMPLE CODE] Parasite thread injection and TCP connection hijacking

On Sat, Aug 6, 2011 at 9:00 AM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Sat, Aug 06, 2011 at 08:45:28AM -0400, Andy Lutomirski wrote:
>> > 2. Decide where to inject the foreign code and save the original code
>> >    with PTRACE_PEEKDATA.  Tracer can poke any mapped area regardless
>> >    of protection flags but it can't add execution permission to the
>> >    code, so it needs to choose memory area which already has X flag
>> >    set.  The example code uses the page the %rip is in.
>>
>> If the process is executing from the vsyscall page, then you'll
>> probably fail.  (Admittedly, this is rather unlikely, given that the
>> vsyscalls are now exactly one instruction.)  Presumably you also
>> fail if executing from a read-only MAP_SHARED mapping.
>
> Heh, yeah, I originally thought about scanning /proc/PID/maps to look
> for the page to use but was lazy and just used %rip.  I think that
> should work.  I'll note the problem in README.
>
>> Windows has a facility to more-or-less call mmap on behalf of
>> another process, and another one to directly inject a thread into a
>> remote process.  It's traditional to use them for this type of
>> manipulation. Perhaps Linux should get the same thing.  (Although
>> you could accomplish much the same thing if you could create a task
>> with your mm but the tracee's fs.)
>
> Actually, the only thing we need on x86_64 is two bytes for the
> syscall instruction because all params are passed through registers
> anyway.  We can just set up parameters for mmap, turn on single step,
> point %rip to syscall in the vsyscall page.  So, either way, I don't
> think this would be too difficult to solve.

Not any more -- that syscall instruction is gone as of 3.1.  You could
search through the vdso to find a syscall, but that seems fragile.

Why not just add a ptrace command to issue a syscall?

--Andy
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