Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF

[Will Drewry <wad@chromium.org>]

On Thu, Jan 12, 2012 at 12:44 PM, Andrew Lutomirski <luto@mit.edu> wrote:
> On Thu, Jan 12, 2012 at 10:32 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>> On Thu, Jan 12, 2012 at 10:18 AM, Andrew Lutomirski <luto@mit.edu> wrote:
>>>
>>> Like this?
>>>
>>> http://lkml.indiana.edu/hypermail/linux/kernel/1003.3/01225.html
>>
>> I don't know the execve_nosecurity patches, so the diff makes little
>> sense to me, but yeah, I wouldn't expect it to be more than a couple
>> of lines. Exactly *how* you set the bit etc is not something I care
>> deeply about, prctl seems about as good as anything.
>>
>>> Note that there's a huge can of worms if execve is allowed but
>>> suid/sgid is not: selinux may elevate privileges on exec of pretty
>>> much anything.  (I think that this is a really awful idea, but it's in
>>> the kernel, so we're stuck with it.)
>>
>> You can do any amount of crazy things with selinux, but the other side
>> of the coin is that it would also be trivial to teach selinux about
>> this same "restricted environment" bit, and just say that a process
>> with that bit set doesn't get to match whatever selinux privilege
>> escalation rules..
>>
>> I really don't think this is just about "execve cannot do setuid". I
>> think it's about the process being marked as restricted.
>>
>> So in your patch, I think that "PR_RESTRICT_EXEC" bit is wrong. It
>> should simply be "PR_RESTRICT_ME", and be done with it, and not try to
>> artificially limit it to be some "execve feature", and more think of
>> it as a "this is a process that has *no* extra privileges at all, and
>> can never get them".
>
> Fair enough.  I'll submit the simpler patch tonight.

This sounds cool.  Do you think you'll go for a new task_struct member
or will it a securebit?  (Seems like securebits might be too tied to
posix file caps, but I figured I'd ask).

I'm planning on going ahead and mocking up your potential patch so I
can respin this series using it and make sure I understand the
interactions.

thanks!
will