Re: [PATCH bpf v3 1/2] bpf_trace: check size for overflow in bpf_kprobe_multi_link_attach

[Yonghong Song]

On 5/18/22 1:00 PM, Eugene Syromiatnikov wrote:
> On Wed, May 18, 2022 at 09:34:22AM -0700, Yonghong Song wrote:
> > On 5/18/22 5:22 AM, Eugene Syromiatnikov wrote:
> > > -	size = cnt * sizeof(*syms);
> > > +	if (check_mul_overflow(cnt, (u32)sizeof(*syms), &size))
> > > +		return -EOVERFLOW;
> >
> > In mm/util.c kvmalloc_node(), we have
> >
> >          /* Don't even allow crazy sizes */
> >          if (unlikely(size > INT_MAX)) {
> >                  WARN_ON_ONCE(!(flags & __GFP_NOWARN));
> >                  return NULL;
> >          }
> >
> > Basically the maximum size to be allocated in INT_MAX.
> >
> > Here, we have 'size' as u32, which means if the size is 0xffff0000,
> > the check_mul_overflow will return false (no overflow) but
> > kvzalloc will still have a warning.
> >
> > I think we should change the type of 'size' to be 'int' which
> > should catch the above case and be consistent with
> > what kvmalloc_node() intends to warn.
>
> Huh, it's a bitmore complicated as check_mul_overflow requires types to
> match; what do you think about
>
> +	if (check_mul_overflow(cnt, (u32)sizeof(*syms), &size) || size > INT_MAX)
>
> ?

This works for me.