From e4f8545e36fb28249864ff7f3a73b6460f6882c3 Mon Sep 17 00:00:00 2001
From: Sean Parkinson <sean@wolfssl.com>
Date: Mon, 15 Feb 2021 10:29:45 +1000
Subject: [PATCH] SP math all: sp_exch fixed up

---
 wolfcrypt/src/dh.c     | 5 +++++
 wolfcrypt/src/dsa.c    | 5 +++++
 wolfcrypt/src/sp_int.c | 9 ++++++++-
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/wolfcrypt/src/dh.c b/wolfcrypt/src/dh.c
index 0c9f18275..3315c2dfa 100644
--- a/wolfcrypt/src/dh.c
+++ b/wolfcrypt/src/dh.c
@@ -2456,7 +2456,12 @@ int wc_DhGenerateParams(WC_RNG *rng, int modSz, DhKey *dh)
 
     if (ret == 0) {
         /* at this point tmp generates a group of order q mod p */
+#ifndef USE_FAST_MATH
+        /* Exchanging is quick when the data pointer can be copied. */
         mp_exch(&tmp, &dh->g);
+#else
+        mp_copy(&tmp, &dh->g);
+#endif
     }
 
     /* clear the parameters if there was an error */
diff --git a/wolfcrypt/src/dsa.c b/wolfcrypt/src/dsa.c
index f62cec92d..dbfa010ef 100644
--- a/wolfcrypt/src/dsa.c
+++ b/wolfcrypt/src/dsa.c
@@ -412,7 +412,12 @@ int wc_MakeDsaParameters(WC_RNG *rng, int modulus_size, DsaKey *dsa)
     } while (mp_cmp_d(&tmp, 1) == MP_EQ);
 
     /* at this point tmp generates a group of order q mod p */
+#ifndef USE_FAST_MATH
+    /* Exchanging is quick when the data pointer can be copied. */
     mp_exch(&tmp, &dsa->g);
+#else
+    mp_copy(&tmp, &dsa->g);
+#endif
 
     mp_clear(&tmp);
     mp_clear(&tmp2);
diff --git a/wolfcrypt/src/sp_int.c b/wolfcrypt/src/sp_int.c
index d51ab9a57..4b760631d 100644
--- a/wolfcrypt/src/sp_int.c
+++ b/wolfcrypt/src/sp_int.c
@@ -2425,12 +2425,19 @@ int sp_exch(sp_int* a, sp_int* b)
     if ((a == NULL) || (b == NULL)) {
         err = MP_VAL;
     }
+    if ((err == MP_OKAY) && ((a->size < b->used) || (b->size < a->used))) {
+        err = MP_VAL;
+    }
 
     ALLOC_SP_INT(t, a->used, err, NULL);
     if (err == MP_OKAY) {
+        int asize = a->size;
+        int bsize = b->size;
         XMEMCPY(t, a, MP_INT_SIZEOF(a->used));
         XMEMCPY(a, b, MP_INT_SIZEOF(b->used));
-        XMEMCPY(b, t, MP_INT_SIZEOF(a->used));
+        XMEMCPY(b, t, MP_INT_SIZEOF(t->used));
+        a->size = asize;
+        b->size = bsize;
     }
 
     FREE_SP_INT(t, NULL);