[pycrypto] Possible problem in src/_fastmath.c

Dwayne C. Litzenberger dlitz at dlitz.net
Thu Oct 16 06:08:32 CST 2008

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.


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.

- Dwayne

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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