Re: Compat 32-bit syscall entry from 64-bit task!? [was: Re:[RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF]

[Chris Evans]

On Mon, Jan 23, 2012 at 8:56 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> On 01/18, Chris Evans wrote:
>>
>> Thanks, Oleg. Seems like this would be a nice change to have. As we
>> can see, people do use ptrace() as a security technology.
>
> OK, I'll send it.
>
>> With this in place, you can also (where possible) set up the tracee
>> with PR_SET_PDEATHSIG==SIGKILL. And then, you have defences again
>> either of the tracer or tracee dying from a stray SIGKILL.
>
> This can only help if the tracer is the natural parent, is it enough?
>
> Indan suggested PTRACE_O_SIGKILL_ON_DEATH, perhaps it makes sense.

Yeah, this takes care of all cases.

One caveat I can think of with the implementation: in the parent
exit() path, the child's SIGKILL needs to be delivered _before_ the
tracer is detached. Otherwise it might feasible wake up and run for a
bit :)


Cheers
Chris

>
> Oleg.
>
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