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SubjectRe: [rfc 4/4] prctl: PR_SET_MM -- Introduce PR_SET_MM_MAP operation, v3
On Thu, Jul 24, 2014 at 12:31:54PM -0700, Kees Cook wrote:
...
> > +
> > +#ifdef CONFIG_STACK_GROWSUP
> > + if (may_adjust_brk(rlimit(RLIMIT_STACK),
> > + stack_vma->vm_end,
> > + prctl_map->start_stack, 0, 0))
> > +#else
> > + if (may_adjust_brk(rlimit(RLIMIT_STACK),
> > + prctl_map->start_stack,
> > + stack_vma->vm_start, 0, 0))
> > +#endif
> > + goto out;
>
> Ah! Sorry, I missed this use of may_adjust_brk here. Perhaps rename
> it, since we're not checking brk here, and pass the RLIMIT_* value to
> the function, which can look it up itself? "check_vma_rlimit" ?

Yeah, a name is a bit confusing, but I guess check_vma_rlimit() is not
much better ;-) What we do inside -- we test if a sum of two intervals
or arguments in this helper so that it won't care about the logical
context it been called from, but then realized that this would be a way
too much of unneeded complexity. So if noone else pop with better suggestion
on name i'll update it to check_vma_rlimit (because it's more general
in compare to may_adjust_brk :-).

> > +
> > + /*
> > + * Finally, make sure the caller has the rights to
> > + * change /proc/pid/exe link: only local root should
> > + * be allowed to.
> > + */
> > + if (prctl_map->exe_fd != (u32)-1) {
> > + struct user_namespace *ns = current_user_ns();
> > + const struct cred *cred = current_cred();
> > +
> > + if (!uid_eq(cred->uid, make_kuid(ns, 0)) ||
> > + !gid_eq(cred->gid, make_kgid(ns, 0)))
> > + goto out;
> > + }
>
> I got tricked for a moment here. :) I see that even if we pass this
> check, prctl_set_mm_exe_file will still do the additional checks too
> during prctl_set_mm_map. Excellent!

Yeah.

> >
> > +#ifdef CONFIG_CHECKPOINT_RESTORE
> > + if (opt == PR_SET_MM_MAP || opt == PR_SET_MM_MAP_SIZE)
> > + return prctl_set_mm_map(opt, (const void __user *)addr, arg4);
> > +#endif
> > +
> > if (!capable(CAP_SYS_RESOURCE))
> > return -EPERM;
> >
> >
>
> I think this is looking good. Thanks for the refactoring!

Thanks a huge for comments!!!


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