Re: [PATCH v2] seccomp: add ptrace options for suspend/resume

[Kees Cook <keescook@chromium.org>]

On Thu, Jun 4, 2015 at 11:03 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> On 06/04, Kees Cook wrote:
>>
>> On Wed, Jun 3, 2015 at 3:09 PM, Tycho Andersen
>> > @@ -556,6 +557,11 @@ static int ptrace_setoptions(struct task_struct *child, unsigned long data)
>> >         if (data & ~(unsigned long)PTRACE_O_MASK)
>> >                 return -EINVAL;
>> >
>> > +#ifdef CONFIG_CHECKPOINT_RESTORE
>> > +       if (data & PTRACE_O_SUSPEND_SECCOMP && !may_suspend_seccomp())
>> > +               return -EPERM;
>> > +#endif
>>
>> I'd like to avoid seeing any #ifdefs added to the .c files. Using a
>> static inline for may_suspend_seccomp() should cause this statement to
>> be eliminated by the compiler.
>
> Agreed, me too, but see below.
>
>> > @@ -590,6 +590,11 @@ void secure_computing_strict(int this_syscall)
>> >  {
>> >         int mode = current->seccomp.mode;
>> >
>> > +#ifdef CONFIG_CHECKPOINT_RESTORE
>> > +       if (unlikely(current->ptrace & PT_SUSPEND_SECCOMP))
>> > +               return;
>> > +#endif
>>
>> Could PT_SUSPEND_SECCOMP be defined to "0" with not
>> CONFIG_CHECKPOINT_RESTORE? Then this wouldn't need ifdefs, and should
>> be similarly eliminated by the compiler.
>
> Yes, but this way we add another ugly ifdef into .h, and if you read
> this code it is not clear that this check should be eliminated by gcc.
>
> I'd suggest
>
>         if (config_enabled(CONFIG_CHECKPOINT_RESTORE) &&
>             unlikely(current->ptrace & PT_SUSPEND_SECCOMP))
>                 return;

Ah! Yes, that makes things nicer.

-Kees

-- 
Kees Cook
Chrome OS Security