[pycrypto] Possible problem in src/_fastmath.c

[Dwayne C. Litzenberger]

On Thu, Oct 16, 2008 at 08:08:32AM -0400, Dwayne C. Litzenberger wrote:
> On Thu, Oct 16, 2008 at 03:39:29AM +0400, Sergey Chernov wrote:
>> See patch:
>> ----------------------------------------------------------------------------
>> diff --git a/src/_fastmath.c b/src/_fastmath.c
>> index d06d697..a0aa181 100755
>> --- a/src/_fastmath.c
>> +++ b/src/_fastmath.c
>> @@ -28,6 +28,7 @@ longObjToMPZ (mpz_t m, PyLongObject * p)
>> 		size = p->ob_size;
>> 	else
>> 		size = -p->ob_size;
>> +	mpz_clear( m );
>> 	for (i = 0; i < size; i++)
>> 	{
>> 		mpz_set_ui (temp, p->ob_digit[i]);
>> ----------------------------------------------------------------------------
>>
>> Current usage do not discover the bug as 'm' is always just-initialized.
>> Still it, as I think, may cause trouble later.
>
> Sergey,
>
> What is the purpose of your patch?  What bug are you referring to?
>
> Are you trying to set m to zero at the top of the loop?  Looking at the GMP 
> documentation (http://gmplib.org/manual/Initializing-Integers.html), I see 
> that mpz_init() and mpz_clear() have similar usages as malloc() and free(), 
> so I'm pretty sure that I do not want to apply your patch as-is.

Perhaps you meant this?

-------------------------------------------------------------------------------
diff --git a/src/_fastmath.c b/src/_fastmath.c
index d06d697..caf8e7b 100755
--- a/src/_fastmath.c
+++ b/src/_fastmath.c
@@ -28,6 +28,7 @@ longObjToMPZ (mpz_t m, PyLongObject * p)
                 size = p->ob_size;
         else
                 size = -p->ob_size;
+       mpz_set_ui (m, 0);
         for (i = 0; i < size; i++)
         {
                 mpz_set_ui (temp, p->ob_digit[i]);
-------------------------------------------------------------------------------


-- 
Dwayne C. Litzenberger <dlitz at dlitz.net>
  Key-signing key   - 19E1 1FE8 B3CF F273 ED17  4A24 928C EC13 39C2 5CF7
  Annual key (2008) - 4B2A FD82 FC7D 9E38 38D9  179F 1C11 B877 E780 4B45
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