Re: mm: NULL ptr deref handling mmaping of special mappings

Cyrill Gorcunov
2014-05-14T22:11:44Z

On Wed, May 14, 2014 at 02:33:54PM -0700, Andy Lutomirski wrote:
> On Wed, May 14, 2014 at 2:31 PM, Andrew Morton
> <akpm@linux-foundation.org> wrote:
> > On Wed, 14 May 2014 17:11:00 -0400 Sasha Levin <sasha.levin@oracle.com> wrote:
> >
> >> > In my linux-next all that code got deleted by Andy's "x86, vdso:
> >> > Reimplement vdso.so preparation in build-time C" anyway. What kernel
> >> > were you looking at?
> >>
> >> Deleted? It appears in today's -next. arch/x86/vdso/vma.c:124 .
> >>
> >> I don't see Andy's patch removing that code either.
> >
> > ah, OK, it got moved from arch/x86/vdso/vdso32-setup.c into
> > arch/x86/vdso/vma.c.
> >
> > Maybe you managed to take a fault against the symbol area between the
> > _install_special_mapping() and the remap_pfn_range() call, but mmap_sem
> > should prevent that.
> >
> > Or the remap_pfn_range() call never happened. Should map_vdso() be
> > running _install_special_mapping() at all if
> > image->sym_vvar_page==NULL?
>
> I'm confused: are we talking about 3.15-rcsomething or linux-next?
> That code changed.
>
> Would this all make more sense if there were just a single vma in
> here? cc: Pavel and Cyrill, who might have to deal with this stuff in
> CRIU

Well, for criu we've not modified any vdso kernel's code (except
setting VM_SOFTDIRTY for this vdso VMA in _install_special_mapping).
And never experienced problems Sasha points. Looks like indeed in
-next code is pretty different from mainline one. To figure out
why I need to fetch -next branch and get some research. I would
try to do that tomorrow (still hoping someone more experienced
in mm system would beat me on that).