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SubjectRe: [PATCH] Yama: turn process ancestry check into function
On Wed, Jul 14, 2010 at 09:19:09AM +0900, Tetsuo Handa wrote:
> Kees Cook wrote:
> > +static int task_is_descendant(struct task_struct *parent,
> > + struct task_struct *child)
> > +{
> > + int rc = 0;
> > + struct task_struct *walker = child;
> > +
> > + if (!parent || !child)
> > + return 0;
>
> parent (== current) is !NULL and
> child (in original code) is !NULL.
> You can remove this check unless you are planning to call
> this function from other places.

I'd like the flexibility to call it with NULLs. But yes, at present, it
never will be NULL.

> > + if (mode == PTRACE_MODE_ATTACH &&
> > + ptrace_scope &&
> > + !task_is_descendant(current, child) &&
> > + !capable(CAP_SYS_PTRACE))
> > + rc = -EPERM;
>
> I don't know how heavy capable(CAP_SYS_PTRACE) is.
> But checking !capable(CAP_SYS_PTRACE) before
> !task_is_descendant(current, child) might be lighter.

That's the order I had before, but in looking at some of the other code, it
seemed like moving it to the end made more logical sense. Since checking
PTRACE attach isn't a common or time-sensitive operation, I figured trying
to tune it wasn't critical.

-Kees

--
Kees Cook
Ubuntu Security Team


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