Commit 9e989810 authored by Geoff Thorpe's avatar Geoff Thorpe
Browse files

BN_div() cleanup: replace the use of BN_sub and BN_add with bn_sub_words 

and bn_add_words to avoid using fake bignums to window other bignums that
can lead to corruption. This change allows all bignum tests to pass with
BN_DEBUG and BN_DEBUG_RAND debugging and valgrind. NB: This should be
tested on a few different architectures and configuration targets, as the
bignum code this deals with is quite preprocessor (and assembly) sensitive.

Submitted by: Nils Narsch
Reviewed by: Geoff Thorpe, Ulf Moeller
parent ec2179cf

crypto/bn/bn_div.c

+45 −36
Original line number Diff line number Diff line
@@ -179,13 +179,15 @@ int BN_div(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m, const BIGNUM *d, 
int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,

	   BN_CTX *ctx)

	{

	int norm_shift,i,j,loop;

	int norm_shift,i,loop;

	BIGNUM *tmp,wnum,*snum,*sdiv,*res;

	BN_ULONG *resp,*wnump;

	BN_ULONG d0,d1;

	int num_n,div_n;



	if (dv)

		bn_check_top(dv);

	if (rm)

		bn_check_top(rm);

	bn_check_top(num);

	bn_check_top(divisor);
@@ -224,15 +226,16 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor, 
	div_n=sdiv->top;

	num_n=snum->top;

	loop=num_n-div_n;



	/* Lets setup a 'window' into snum

	 * This is the part that corresponds to the current

	 * 'area' being divided */

	BN_init(&wnum);

	wnum.flags = BN_FLG_STATIC_DATA; /* prevent accidental "expands" */

	wnum.neg   = 0;

	wnum.d     = &(snum->d[loop]);

	wnum.top   = div_n;

#ifdef BN_DEBUG_RAND

	/* only needed when BN_ucmp messes up the values between top and max */

	wnum.dmax  = snum->dmax - loop; /* so we don't step out of bounds */

#endif



	/* Get the top 2 words of sdiv */

	/* div_n=sdiv->top; */
@@ -251,22 +254,32 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor, 
	/* space for temp */

	if (!bn_wexpand(tmp,(div_n+1))) goto err;



	bn_correct_top(&wnum);

	if (BN_ucmp(&wnum,sdiv) >= 0)

		{

		if (!BN_usub(&wnum,&wnum,sdiv)) goto err;

#ifdef BN_DEBUG_RAND

		/* If BN_DEBUG_RAND is defined BN_ucmp changes (via

		 * bn_pollute) the const bignum arguments =>

		 * clean the values between top and max again */

		bn_clear_top2max(&wnum);

#endif

		bn_sub_words(wnum.d, wnum.d, sdiv->d, div_n);

		*resp=1;

		res->d[res->top-1]=1;

		}

	else

		res->top--;

	/* if res->top == 0 then clear the neg value otherwise decrease

	 * the resp pointer */

	if (res->top == 0)

		res->neg = 0;

	else

		resp--;



	for (i=0; i<loop-1; i++)

	for (i=0; i<loop-1; i++, wnump--, resp--)

		{

		BN_ULONG q,l0;

		/* the first part of the loop uses the top two words of

		 * snum and sdiv to calculate a BN_ULONG q such that

		 * | wnum - sdiv * q | < sdiv */

#if defined(BN_DIV3W) && !defined(OPENSSL_NO_ASM)

		BN_ULONG bn_div_3_words(BN_ULONG*,BN_ULONG,BN_ULONG);

		q=bn_div_3_words(wnump,d1,d0);
@@ -350,31 +363,26 @@ X) -> 0x%08X\n", 
#endif /* !BN_DIV3W */



		l0=bn_mul_words(tmp->d,sdiv->d,div_n,q);

		wnum.d--; wnum.top++; wnum.dmax++;

		tmp->d[div_n]=l0;

		/* XXX: Couldn't we replace this with;

		 *    tmp->top = div_n;

		 *    bn_fix_top(tmp);

		 */

		for (j=div_n+1; j>0; j--)

			if (tmp->d[j-1]) break;

		tmp->top=j;



		j=wnum.top;

		bn_correct_top(&wnum);

		if (!BN_sub(&wnum,&wnum,tmp)) goto err;



		snum->top=snum->top+wnum.top-j;



		if (wnum.neg)

		wnum.d--;

		/* ingore top values of the bignums just sub the two 

		 * BN_ULONG arrays with bn_sub_words */

		if (bn_sub_words(wnum.d, wnum.d, tmp->d, div_n+1))

			{

			/* Note: As we have considered only the leading

			 * two BN_ULONGs in the calculation of q, sdiv * q

			 * might be greater than wnum (but then (q-1) * sdiv

			 * is less or equal than wnum)

			 */

			q--;

			j=wnum.top;

			if (!BN_add(&wnum,&wnum,sdiv)) goto err;

			snum->top+=wnum.top-j;

			if (bn_add_words(wnum.d, wnum.d, sdiv->d, div_n))

				/* we can't have an overflow here (assuming

				 * that q != 0, but if q == 0 then tmp is

				 * zero anyway) */

				(*wnump)++;

			}

		*(resp--)=q;

		wnump--;

		/* store part of the result */

		*resp = q;

		}

	if (rm != NULL)

		{
@@ -391,6 +399,7 @@ X) -> 0x%08X\n", 
	BN_CTX_end(ctx);

	return(1);

err:

	if (rm)

		bn_check_top(rm);

	BN_CTX_end(ctx);

	return(0);