linux-kernel - Re: [PATCH 1/2] lib/test

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Date:   Tue, 30 Aug 2022 09:32:19 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Kent Overstreet <kent.overstreet@...ux.dev>
Cc:     linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH 1/2] lib/test_printf.c: Add ip6 tests

On 30/08/2022 03.47, Sergey Senozhatsky wrote:
> On (22/08/29 20:31), Kent Overstreet wrote:
>> diff --git a/lib/test_printf.c b/lib/test_printf.c
>> index 4bd15a593f..6a56dbf076 100644
>> --- a/lib/test_printf.c
>> +++ b/lib/test_printf.c
>> @@ -18,6 +18,7 @@
>>  #include <linux/dcache.h>
>>  #include <linux/socket.h>
>>  #include <linux/in.h>
>> +#include <linux/in6.h>
>>  
>>  #include <linux/gfp.h>
>>  #include <linux/mm.h>
>> @@ -61,6 +62,9 @@ do_test(int bufsize, const char *expect, int elen,
>>  		pr_warn("vsnprintf(buf, %d, \"%s\", ...) returned %d, expected %d\n",
>>  			bufsize, fmt, ret, elen);
>>  		return 1;
>> +		pr_warn("vsnprintf(buf, %d, \"%s\", ...) returned %d, expected %d (%s != %s)\n",
>> +			bufsize, fmt, ret, elen, test_buffer, expect);
>> +		return 1;
>>  	}
> 
> I assume you intended to replace first pr_warn() with the second one?

Probably, but that's not ok. The test framework does not trust
vsnprintf(), especially not when it does not behave as expected. So I
very much carefully do not treat the buffer as a nul-terminated string
until I have verified that it does have a nul character (that's tested a
few lines below), and then when I compare the buffer contents can I pass
it as a %s argument. Also note how that test takes the 'we may be
testing a truncated write' into consideration, by printing the expect
string via %.*s.

tl;dr, please just remove that hunk.

Rasmus