On Fri, 18 Aug 2017 12:28:29 -0400 Rik van Riel <riel@xxxxxxxxxx> wrote:
> On Thu, 2017-08-17 at 15:50 -0700, Andrew Morton wrote:
> > 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?
>
> Uh, what?
>
Braino. I meant MADV_KEEPONFORK. Calling MADV_KEEPONFORK against an
other-than-anon vma is a presumptive userspace bug and the kernel
should report that.
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