linux-kernel - Re: [PATCH v3 3/3] lib/string_helpers.c: Change semantics of string_escape

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Date:	Sat, 21 Feb 2015 02:35:45 +0100
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH v3 3/3] lib/string_helpers.c: Change semantics of string_escape_mem

On Tue, Feb 10 2015, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:

>> >> ---
>> >> index ab0d30e1e18f..5f759c3c2f60 100644
>> >> --- a/lib/test-string_helpers.c
>> >> +++ b/lib/test-string_helpers.c
>> >> @@ -264,12 +264,12 @@ static __init void test_string_escape(const char *name,
>> >>  				      const struct test_string_2 *s2,
>> >>  				      unsigned int flags, const char *esc)
>> >>  {
>> >> -	int q_real = 512;
>> >> -	char *out_test = kmalloc(q_real, GFP_KERNEL);
>> >> -	char *out_real = kmalloc(q_real, GFP_KERNEL);
>> >> +	size_t out_size = 512;
>> >> +	char *out_test = kmalloc(out_size, GFP_KERNEL);
>> >> +	char *out_real = kmalloc(out_size, GFP_KERNEL);
>> >>  	char *in = kmalloc(256, GFP_KERNEL);
>> >> -	char *buf = out_real;
>> >>  	int p = 0, q_test = 0;
>> >> +	int q_real;
>> >>  
>> >>  	if (!out_test || !out_real || !in)
>> >>  		goto out;
>> >> @@ -301,29 +301,26 @@ static __init void test_string_escape(const char *name,
>> >>  		q_test += len;
>> >>  	}
>> >>  
>> >> -	q_real = string_escape_mem(in, p, &buf, q_real, flags, esc);
>> >> +	q_real = string_escape_mem(in, p, out_real, out_size, flags, esc);
>> >>  
>> >>  	test_string_check_buf(name, flags, in, p, out_real, q_real, out_test,
>> >>  			      q_test);
>> >> +
>> >> +	memset(out_real, 'Z', out_size);
>> >> +	q_real = string_escape_mem(in, p, out_real, 0, flags, esc);
>> >> +	if (q_real != q_test)
>> >> +		pr_warn("Test '%s' failed: flags = %u, osz = 0, expected %d, got %d\n",
>> >> +			name, flags, q_test, q_real);
>> >> +	if (memchr_inv(out_real, 'Z', out_size))
>> >> +		pr_warn("Test '%s' failed: osz = 0 but string_escape_mem wrote to the buffer\n",
>> >> +			name);
>> >> +
>> >
>> > So, why couldn't we split this to separate test case? It seems I already
>> > pointed this out.
>> >
>> 
>> This actually provides better coverage
>
> I do not see much advantage of doing so. You may create a loop with
> random number for in-size and check. So, I prefer to see separate case
> for that.

It's not about the size, it's about exercising all the various escape_*
helpers, to ensure that they all respect the end of the buffer, while
still returning the correct would-be output size. For that, one needs to
call string_escape_mem with various combinations of flags and input
buffers. The logic for that is already in place in test_string_escape
and its caller, and I see no point in duplicating all that.

If you insist on a separate function for doing the overflow testing,
I'll just rip it out from my code and let you add such a test later.

I've updated 2/3 with the early returns you suggested, but I'll wait a
little before sending out a v4.

Rasmus
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