Return shared OIDs when decoding.

When an OID is decoded see if it exists in the registered OID table
and if so return the shared OID instead of dynamically allocating
an ASN1_OBJECT.
Reviewed-by: NRich Salz <rsalz@openssl.org>

crypto/asn1/a_object.c

@@ -271,7 +271,7 @@ ASN1_OBJECT *d2i_ASN1_OBJECT(ASN1_OBJECT **a, const unsigned char **pp,
 ASN1_OBJECT *c2i_ASN1_OBJECT(ASN1_OBJECT **a, const unsigned char **pp,
                              long len)
 {
-    ASN1_OBJECT *ret = NULL;
+    ASN1_OBJECT *ret = NULL, tobj;
     const unsigned char *p;
     unsigned char *data;
     int i, length;
@@ -288,6 +288,29 @@ ASN1_OBJECT *c2i_ASN1_OBJECT(ASN1_OBJECT **a, const unsigned char **pp,
     }
     /* Now 0 < len <= INT_MAX, so the cast is safe. */
     length = (int)len;
+    /*
+     * Try to lookup OID in table: these are all valid encodings so if we get
+     * a match we know the OID is valid.
+     */
+    tobj.nid = NID_undef;
+    tobj.data = p;
+    tobj.length = length;
+    tobj.flags = 0;
+    i = OBJ_obj2nid(&tobj);
+    if (i != NID_undef) {
+        /*
+         * Return shared registered OID object: this improves efficiency
+         * because we don't have to return a dynamically allocated OID
+         * and NID lookups can use the cached value.
+         */
+        ret = OBJ_nid2obj(i);
+        if (a) {
+            ASN1_OBJECT_free(*a);
+            *a = ret;
+        }
+        *pp += len;
+        return ret;
+    }
     for (i = 0; i < length; i++, p++) {
         if (*p == 0x80 && (!i || !(p[-1] & 0x80))) {
             ASN1err(ASN1_F_C2I_ASN1_OBJECT, ASN1_R_INVALID_OBJECT_ENCODING);