Uninitialized memory bug found in /mpn/generic/mod_1_1.c

marco.bodrato at tutanota.com marco.bodrato at tutanota.com
Thu Aug 31 19:33:46 CEST 2023


31 ago 2023, 18:06 da vincent at vinc17.net:

> I don't think that this is sufficient for the test.
> The code Brett mentioned is for MOD_1_1P_METHOD = 2.

The code Brett mentioned is mixed, I fear.
Looking at mpn/generic/mod_1_1.c,if MOD_1_1P_METHOD == 1, the value[2] in the array is always set and always used;
if MOD_1_1P_METHOD == 2, the value[2] is set only if cnt!=0, and it is used only if cnt!=0.
There are also some assembler code implementations, each one with its couple of functions.

> So, in mpn/generic/mod_1_1.c, I also changed
> # define MOD_1_1P_METHOD 1    /* need to make sure this is 2 for asm testing */

Not enough, MOD_1_1P_METHOD may be defined by gmp-mparam.h
One should also check how MOD_1N_TO_MOD_1_1_THRESHOLD interact with the tests.

> ASSERT (bmodb[2] != -1);

> But even with that, I don't get any failure.
Actually it is possible to trigger this, if you put it in the wrong place, I mean, outside the branch actually using the value... but it is not interesting.


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