Fix for in-place ecc_add_eh.

* ecc-add-eh.c (ecc_add_eh): Fix in-place operation by reordering
two multiplies. Previously, in-place operation resulted in an
invalid call to mpn_mul with overlapping operands. Reported by
Sergei Trofimovich.

ChangeLog

+2017-07-18  Niels Möller  <nisse@lysator.liu.se>
+
+	* ecc-add-eh.c (ecc_add_eh): Fix in-place operation by reordering
+	two multiplies. Previously, in-place operation resulted in an
+	invalid call to mpn_mul with overlapping operands. Reported by
+	Sergei Trofimovich.
+
 2017-06-09  Niels Möller  <nisse@lysator.liu.se>
 
 	* pss.c (pss_verify_mgf1): Check for m being too large, fixing an

ecc-add-eh.c

@@ -98,8 +98,8 @@ ecc_add_eh (const struct ecc_curve *ecc,
   ecc_modp_mul (ecc, x3, B, z1);
 
   /* y3 */
-  ecc_modp_mul (ecc, B, F, C); /* ! */
-  ecc_modp_mul (ecc, y3, B, z1);
+  ecc_modp_mul (ecc, B, F, z1); /* ! */
+  ecc_modp_mul (ecc, y3, B, C); /* Clobbers z1 in case r == p. */
 
   /* z3 */
   ecc_modp_mul (ecc, B, F, G);