linux-kernel - Re: [PATCH v4 2/6] treewide: use prandom_u32

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Message-ID: <Y0DssPFp2rY+TrPp@zx2c4.com>
Date:   Fri, 7 Oct 2022 21:21:20 -0600
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
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Subject: Re: [PATCH v4 2/6] treewide: use prandom_u32_max() when possible

On Fri, Oct 07, 2022 at 03:47:44PM -0700, Kees Cook wrote:
> > diff --git a/lib/test_vmalloc.c b/lib/test_vmalloc.c
> > index 4f2f2d1bac56..56ffaa8dd3f6 100644
> > --- a/lib/test_vmalloc.c
> > +++ b/lib/test_vmalloc.c
> > @@ -151,9 +151,7 @@ static int random_size_alloc_test(void)
> >  	int i;
> >  
> >  	for (i = 0; i < test_loop_count; i++) {
> > -		n = prandom_u32();
> > -		n = (n % 100) + 1;
> > -
> > +		n = prandom_u32_max(n % 100) + 1;
> >  		p = vmalloc(n * PAGE_SIZE);
> >  
> >  		if (!p)
> 
> This looks wrong. Cocci says:
> 
> -               n = prandom_u32();
> -               n = (n % 100) + 1;
> +               n = prandom_u32_max(100) + 1;

I agree that's wrong, but what rule did you use to make Cocci generate
that?

Jason