linux-kernel - Re: [PATCH] lib: vsprintf: fix invalid arg check

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Message-ID: <20101112174203.GA10430@albatros>
Date:	Fri, 12 Nov 2010 20:42:03 +0300
From:	Vasiliy Kulikov <segooon@...il.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	kernel-janitors@...r.kernel.org,
	André Goddard Rosa <andre.goddard@...il.com>,
	Joe Perches <joe@...ches.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Bjorn Helgaas <bjorn.helgaas@...com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib: vsprintf: fix invalid arg check

On Thu, Nov 11, 2010 at 13:34 -0800, David Rientjes wrote:
> On Fri, 12 Nov 2010, Vasiliy Kulikov wrote:
> > OK, if the main reason here is return value type, then the correct
> > handling should be:
> > 
> > 	/* Reject out-of-range values early.  Large positive sizes are
> > 	   used for unknown buffer sizes. */
> > -	if (WARN_ON_ONCE((int) size < 0))
> > +	if (WARN_ON_ONCE(size > INT_MAX)
> > 		return 0;
> > 
> > This should catch all underflows and too big integers.
> > 
> 
> That is equivalent since size_t is always unsigned;

Not equivalent:

void test_size(size_t size)
{
    char buffer[128];
    sprintf(buffer, "size %lx is BAD", size);
    snprintf(buffer, size, "size %lx is OK", size);
    pr_info("%s\n", buffer);
    if (size > INT_MAX)
        pr_info("%lx is catched by (size) > INT_MAX", size);
}

static int init(void) {
        test_size(0x7FFFFFFF);
        test_size(0x80000000);
        test_size(0x80000001);
        test_size(0xFFFFFFFF);
        test_size(0x100000000);
        test_size(0x100000001);
        test_size(0x17fffffff);
        test_size(0x180000000);
        test_size(0x180000001);

        return 0;
}


Output on x86_64:

[12486.542047] size 7fffffff is OK
[12486.542051] size 80000000 is BAD
[12486.542053] 80000000 is catched by (size) > INT_MAX
[12486.542055] size 80000001 is BAD
[12486.542057] 80000001 is catched by (size) > INT_MAX
[12486.542059] size ffffffff is BAD
[12486.542061] ffffffff is catched by (size) > INT_MAX
[12486.542063] size 100000000 is OK
[12486.542065] 100000000 is catched by (size) > INT_MAX
[12486.542067] size 100000001 is OK
[12486.542069] 100000001 is catched by (size) > INT_MAX
[12486.542071] size 17fffffff is OK
[12486.542073] 17fffffff is catched by (size) > INT_MAX
[12486.542075] size 180000000 is BAD
[12486.542077] 180000000 is catched by (size) > INT_MAX
[12486.542079] size 180000001 is BAD
[12486.542081] 180000001 is catched by (size) > INT_MAX


-- 
Vasiliy
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