linux-kernel - Re: [PATCH] overflow.h: Rename __ab_c_size() to __calc

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Date:   Fri, 5 Apr 2019 09:13:24 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        LKML <linux-kernel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH] overflow.h: Rename __ab_c_size() to __calc_size()

On Fri, Apr 5, 2019 at 1:24 AM Borislav Petkov <bp@...en8.de> wrote:
>
> On Fri, Apr 05, 2019 at 10:09:31AM +0200, Rasmus Villemoes wrote:
> > On 05/04/2019 09.52, Borislav Petkov wrote:
> > > On Fri, Apr 05, 2019 at 08:26:45AM +0200, Rasmus Villemoes wrote:
> >
> > >> It computes a*b+c with overflow checking at each step. calc_size
> > >> is way too generic and doesn't say anything at all about how the
> > >> calc(ulation) is done.
> > >
> > > Ok, whatever.
> > >
> > > Then it would need at least a comment above it to state what it does. I
> > > don't want to go and parse the macros each time.
> >
> > It's an internal helper, and struct_size is fully kernel-doc'ed. But
> > yeah, a comment wouldn't hurt, and let's rename the parameters so they
> > match the abc naming.
> >
> > diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> > index 40b48e2133cb..6534a727cadb 100644
> > --- a/include/linux/overflow.h
> > +++ b/include/linux/overflow.h
> > @@ -278,11 +278,15 @@ static inline __must_check size_t
> > array3_size(size_t a, size_t b, size_t c)
> >         return bytes;
> >  }
> >
> > -static inline __must_check size_t __ab_c_size(size_t n, size_t size,
> > size_t c)
> > +/*
> > + * Compute a*b+c, returning SIZE_MAX on overflow. Internal helper for
> > + * struct_size() below.
> > + */

May as well make this kern-doc too?

> > +static inline __must_check size_t __ab_c_size(size_t a, size_t b, size_t c)
> >  {
> >         size_t bytes;
> >
> > -       if (check_mul_overflow(n, size, &bytes))
> > +       if (check_mul_overflow(a, b, &bytes))
> >                 return SIZE_MAX;
> >         if (check_add_overflow(bytes, c, &bytes))
> >                 return SIZE_MAX;
> >
> >
>
> Reported-by: Borislav Petkov <bp@...e.de>
> Acked-by: Borislav Petkov <bp@...e.de>

Acked-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook