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SubjectRe: [PATCH] Yama: turn process ancestry check into function
Quoting Kees Cook (kees.cook@canonical.com):
> On Wed, Jul 14, 2010 at 09:19:09AM +0900, Tetsuo Handa wrote:
> > > + 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.

Yes the reason to keep it like this is that capable(CAP_SYS_PTRACE)
will set PF_SUPERPRIV if it passes. You don't want to do that unless
the capability was actually required.

-serge


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