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SP int: fixes from review by Claude

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1. sp_cond_swap_ct_ex (line ~5524) — XOR typo: b->sign ^= b->sign always
zeroed the sign. Fixed to b->sign ^= t->sign to correctly swap signs.
2. sp_mod_d (line ~7271) — Negative modulo correction was applied even
when the remainder was 0. Added (*r != 0) guard to avoid producing d
instead of 0.
3. sp_lshb (line ~8444) — Left-shift size check was off. Refactored to
correctly distinguish between pure-digit shifts and bit-within-digit
shifts when checking if the result fits, using separate overflow checks
for each case.
4. _sp_mulmod_tmp (line ~12160) — Zero inputs caused an allocation of
size 0, which is problematic. Added an early path: if either operand is
zero, set result to zero and skip the allocation/multiply entirely.
5. sp_mod_2d — copy path (line ~14762) — XMEMCPY copied digits *
SP_WORD_SIZEOF bytes but a may have fewer than digits used digits. Fixed
to copy min(a->used, digits) digits to avoid reading uninitialized
memory.
6. sp_mod_2d — negation loop (line ~14782) — Negation loop iterated
over r->used, which could exceed digits. Fixed to loop over min(r->used,
digits).
7. _sp_sqrmod (line ~17314) — Same zero-input issue as _sp_mulmod_tmp.
Added early zero path to skip the allocation/squaring when input is
zero.
8. sp_lcm (line ~19838) — Typo in sign check: b->sign >= MP_NEG
(comparing against a value that is 1, so >= 1 would also match MP_ZPOS)
changed to b->sign == MP_NEG.
This commit is contained in:
Sean Parkinson
2026-04-16 19:01:53 +10:00
parent f086e91cbf
commit c119a21931
1 changed files with 52 additions and 34 deletions
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wolfcrypt/src/sp_int.c
+52 -34
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@@ -8546,14 +8546,17 @@ static int sp_lshb(sp_int* a, int n)
if (a->used != 0) {
/* Calculate number of digits to shift. */
sp_size_t s = (sp_size_t)n >> SP_WORD_SHIFT;
/* Get count of bits to move in digit. */
n &= (int)SP_WORD_MASK;
/* Ensure number has enough digits for result. */
if (a->used + s >= a->size) {
if ((n != 0) && (a->used + s >= a->size)) {
err = MP_VAL;
}
else if ((s > 0) && (a->used + s > a->size)) {
err = MP_VAL;
}
if (err == MP_OKAY) {
/* Get count of bits to move in digit. */
n &= (int)SP_WORD_MASK;
/* Check whether this is a complicated case. */
if (n != 0) {
unsigned int i;
@@ -12258,24 +12261,30 @@ static int _sp_mulmod_tmp(const sp_int* a, const sp_int* b, const sp_int* m,
sp_int* r)
{
int err = MP_OKAY;
/* Create temporary for multiplication result. */
DECL_SP_INT(t, a->used + b->used);
ALLOC_SP_INT(t, a->used + b->used, err, NULL);
if (err == MP_OKAY) {
err = sp_init_size(t, (sp_size_t)(a->used + b->used));
if (sp_iszero(a) || sp_iszero(b)) {
_sp_zero(r);
}
else {
/* Create temporary for multiplication result. */
DECL_SP_INT(t, a->used + b->used);
/* Multiply and reduce. */
if (err == MP_OKAY) {
err = sp_mul(a, b, t);
}
if (err == MP_OKAY) {
err = sp_mod(t, m, r);
}
ALLOC_SP_INT(t, a->used + b->used, err, NULL);
if (err == MP_OKAY) {
err = sp_init_size(t, (sp_size_t)(a->used + b->used));
}
/* Dispose of an allocated SP int. */
FREE_SP_INT(t, NULL);
/* Multiply and reduce. */
if (err == MP_OKAY) {
err = sp_mul(a, b, t);
}
if (err == MP_OKAY) {
err = sp_mod(t, m, r);
}
/* Dispose of an allocated SP int. */
FREE_SP_INT(t, NULL);
}
return err;
}
@@ -14851,7 +14860,8 @@ int sp_mod_2d(const sp_int* a, int e, sp_int* r)
if (err == MP_OKAY) {
/* Copy a into r if not same pointer. */
if (a != r) {
XMEMCPY(r->dp, a->dp, digits * (word32)SP_WORD_SIZEOF);
sp_size_t cnt = (a->used < digits) ? a->used : digits;
XMEMCPY(r->dp, a->dp, cnt * (word32)SP_WORD_SIZEOF);
r->used = a->used;
#ifdef WOLFSSL_SP_INT_NEGATIVE
r->sign = a->sign;
@@ -14870,9 +14880,10 @@ int sp_mod_2d(const sp_int* a, int e, sp_int* r)
if (a->sign == MP_NEG) {
unsigned int i;
sp_int_digit carry = 0;
sp_size_t cnt = (r->used < digits) ? r->used : digits;
/* Negate value. */
for (i = 0; i < r->used; i++) {
for (i = 0; i < cnt; i++) {
sp_int_digit next = r->dp[i] > 0;
r->dp[i] = (sp_int_digit)0 - r->dp[i] - carry;
carry |= next;
@@ -17401,24 +17412,31 @@ int sp_sqr(const sp_int* a, sp_int* r)
static int _sp_sqrmod(const sp_int* a, const sp_int* m, sp_int* r)
{
int err = MP_OKAY;
/* Create temporary for multiplication result. */
DECL_SP_INT(t, a->used * 2);
ALLOC_SP_INT(t, a->used * 2, err, NULL);
if (err == MP_OKAY) {
err = sp_init_size(t, a->used * 2U);
if (sp_iszero(a)) {
_sp_zero(r);
}
else {
/* Create temporary for multiplication result. */
DECL_SP_INT(t, a->used * 2);
ALLOC_SP_INT(t, a->used * 2, err, NULL);
if (err == MP_OKAY) {
err = sp_init_size(t, a->used * 2U);
}
/* Square and reduce. */
if (err == MP_OKAY) {
err = sp_sqr(a, t);
}
if (err == MP_OKAY) {
err = sp_mod(t, m, r);
}
/* Dispose of an allocated SP int. */
FREE_SP_INT(t, NULL);
}
/* Square and reduce. */
if (err == MP_OKAY) {
err = sp_sqr(a, t);
}
if (err == MP_OKAY) {
err = sp_mod(t, m, r);
}
/* Dispose of an allocated SP int. */
FREE_SP_INT(t, NULL);
return err;
}