From 906ea4ad0392dc8ad84fba8d87e24ee33b889860 Mon Sep 17 00:00:00 2001
From: Chris Conlon <chris@wolfssl.com>
Date: Fri, 18 Mar 2022 09:17:11 -0600
Subject: [PATCH] smallstack reduction for wolfSSL_EC_POINT_invert

---
 src/ssl.c | 30 +++++++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)

diff --git a/src/ssl.c b/src/ssl.c
index cfff03c11..757830852 100644
--- a/src/ssl.c
+++ b/src/ssl.c
@@ -40735,7 +40735,11 @@ int wolfSSL_EC_POINT_invert(const WOLFSSL_EC_GROUP *group, WOLFSSL_EC_POINT *a,
                             WOLFSSL_BN_CTX *ctx)
 {
     ecc_point* p;
-    mp_int prime;
+#ifdef WOLFSSL_SMALL_STACK
+    mp_int* prime = NULL;
+#else
+    mp_int prime[1];
+#endif
 
     (void)ctx;
 
@@ -40747,22 +40751,42 @@ int wolfSSL_EC_POINT_invert(const WOLFSSL_EC_GROUP *group, WOLFSSL_EC_POINT *a,
 
     p = (ecc_point*)a->internal;
 
+#ifdef WOLFSSL_SMALL_STACK
+    prime = (mp_int*)XMALLOC(sizeof(mp_int), NULL, DYNAMIC_TYPE_BIGINT);
+    if (prime == NULL) {
+        return WOLFSSL_FAILURE;
+    }
+#endif
+
     /* read the curve prime and a */
-    if (mp_init_multi(&prime, NULL, NULL, NULL, NULL, NULL) != MP_OKAY) {
+    if (mp_init_multi(prime, NULL, NULL, NULL, NULL, NULL) != MP_OKAY) {
         WOLFSSL_MSG("mp_init_multi error");
+    #ifdef WOLFSSL_SMALL_STACK
+        XFREE(prime, NULL, DYNAMIC_TYPE_BIGINT);
+    #endif
         return WOLFSSL_FAILURE;
     }
 
-    if (mp_sub(&prime, p->y, p->y) != MP_OKAY) {
+    if (mp_sub(prime, p->y, p->y) != MP_OKAY) {
         WOLFSSL_MSG("mp_sub error");
+    #ifdef WOLFSSL_SMALL_STACK
+        XFREE(prime, NULL, DYNAMIC_TYPE_BIGINT);
+    #endif
         return WOLFSSL_FAILURE;
     }
 
     if (SetECPointExternal(a) != WOLFSSL_SUCCESS) {
         WOLFSSL_MSG("SetECPointExternal error");
+    #ifdef WOLFSSL_SMALL_STACK
+        XFREE(prime, NULL, DYNAMIC_TYPE_BIGINT);
+    #endif
         return WOLFSSL_FAILURE;
     }
 
+#ifdef WOLFSSL_SMALL_STACK
+    XFREE(prime, NULL, DYNAMIC_TYPE_BIGINT);
+#endif
+
     return WOLFSSL_SUCCESS;
 }