Re: UBSAN: array-index-out-of-bounds in kernel/bpf/arraymap.c:177

[Andrii Nakryiko]

On Mon, May 18, 2020 at 5:09 PM Qian Cai <cai@xxxxxx> wrote:
>
> On Mon, May 18, 2020 at 7:55 PM Andrii Nakryiko
> <andrii.nakryiko@xxxxxxxxx> wrote:
> >
> > On Sun, May 17, 2020 at 7:45 PM Qian Cai <cai@xxxxxx> wrote:
> > >
> > > With Clang 9.0.1,
> > >
> > > return array->value + array->elem_size * (index & array->index_mask);
> > >
> > > but array->value is,
> > >
> > > char value[0] __aligned(8);
> >
> > This, and ptrs and pptrs, should be flexible arrays. But they are in a
> > union, and unions don't support flexible arrays. Putting each of them
> > into anonymous struct field also doesn't work:
> >
> > /data/users/andriin/linux/include/linux/bpf.h:820:18: error: flexible
> > array member in a struct with no named members
> >    struct { void *ptrs[] __aligned(8); };
> >
> > So it probably has to stay this way. Is there a way to silence UBSAN
> > for this particular case?
>
> I am not aware of any way to disable a particular function in UBSAN
> except for the whole file in kernel/bpf/Makefile,
>
> UBSAN_SANITIZE_arraymap.o := n
>
> If there is no better way to do it, I'll send a patch for it.


That's probably going to be too drastic, we still would want to
validate the rest of arraymap.c code, probably. Not sure, maybe
someone else has better ideas.