On Sat, 30 Sep 2023, Kees Cook wrote:
> On Sat, Sep 30, 2023 at 11:14:47AM +0200, Christophe JAILLET wrote:
> > Prepare for the coming implementation by GCC and Clang of the __counted_by
> > attribute. Flexible array members annotated with __counted_by can have
> > their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> > (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> > functions).
> >
> > Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
> > ---
> > This patch is part of a work done in parallel of what is currently worked
> > on by Kees Cook.
> >
> > My patches are only related to corner cases that do NOT match the
> > semantic of his Coccinelle script[1].
>
> Nice!
>
> struct comedi_lrange {
> int length;
> struct comedi_krange range[];
> };
> ...
> static const struct comedi_lrange range_rti800_ai_10_bipolar = {
> 4, {
> BIP_RANGE(10),
> BIP_RANGE(1),
> BIP_RANGE(0.1),
> BIP_RANGE(0.02)
> }
> };
>
> I'm struggling to come up with a way for Coccinelle to find this kind of
> thing in other places...
Kees, what exactly are you trying to match? Static allocations?
julia
>
> > In this case, it is been spotted because of comedi_alloc_spriv().
> > All other usages of struct comedi_lrange seem to be static definition of
> > the structure that explicitly set the .length field.
>
> Ah-ha, I found it in drivers/comedi/drivers/das16.c das16_ai_range():
>
> lrange = comedi_alloc_spriv(s,
> struct_size(lrange, range, 1));
>
> I was also able to find this:
>
> union jr3_pci_single_range {
> struct comedi_lrange l;
> char _reserved[offsetof(struct comedi_lrange, range[1])];
> };
>
> Which looks a lot like DEFINE_FLEX:
> https://lore.kernel.org/linux-hardening/20230912115937.1645707-2-przemyslaw.kitszel@xxxxxxxxx/
> But that above for stack varaibles rather than globals. But I'm way off
> topic now. ;)
>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
>
> >
> > [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> > ---
> > include/linux/comedi/comedidev.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/comedi/comedidev.h b/include/linux/comedi/comedidev.h
> > index 0a1150900ef3..c08416a7364b 100644
> > --- a/include/linux/comedi/comedidev.h
> > +++ b/include/linux/comedi/comedidev.h
> > @@ -633,7 +633,7 @@ extern const struct comedi_lrange range_unknown;
> > */
> > struct comedi_lrange {
> > int length;
> > - struct comedi_krange range[];
> > + struct comedi_krange range[] __counted_by(length);
> > };
> >
> > /**
> > --
> > 2.34.1
> >
>
> --
> Kees Cook
>
