On Tue, 15 Aug 2017 22:18:19 -0400 Rik van Riel <riel@xxxxxxxxxx> wrote:
> > > --- a/mm/madvise.c
> > > +++ b/mm/madvise.c
> > > @@ -80,6 +80,17 @@ static long madvise_behavior(struct
> > > vm_area_struct *vma,
> > > __ }
> > > __ new_flags &= ~VM_DONTCOPY;
> > > __ break;
> > > + case MADV_WIPEONFORK:
> > > + /* MADV_WIPEONFORK is only supported on anonymous
> > > memory. */
> > > + if (vma->vm_file || vma->vm_flags & VM_SHARED) {
> > > + error = -EINVAL;
> > > + goto out;
> > > + }
> > > + new_flags |= VM_WIPEONFORK;
> > > + break;
> > > + case MADV_KEEPONFORK:
> > > + new_flags &= ~VM_WIPEONFORK;
> > > + break;
> > > __ case MADV_DONTDUMP:
> > > __ new_flags |= VM_DONTDUMP;
> > > __ break;
> >
> > It seems odd to permit MADV_KEEPONFORK against other-than-anon vmas?
>
> Given that the only way to set VM_WIPEONFORK is through
> MADV_WIPEONFORK, calling MADV_KEEPONFORK on an
> other-than-anon vma would be equivalent to a noop.
>
> If new_flags == vma->vm_flags, madvise_behavior() will
> immediately exit.
Yes, but calling MADV_WIPEONFORK against an other-than-anon vma is
presumably a userspace bug. A bug which will probably result in
userspace having WIPEONFORK memory which it didn't want. The kernel
can trivially tell userspace that it has this bug so why not do so?
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