Fix SChannel pointer mismatches and SCRAM fallback

* Fix `tls_schannel.c` passing `tls_t*` instead of `struct conn_interface*`
* Prevent "Memory allocation error" in `auth.c` by gracefully falling back
* Query if tls backend supports channel binding before indicating support

Author: jjj333-p

src/auth.c

@@ -602,8 +602,17 @@ static int _make_scram_init_msg(struct scram_user_data *scram)
         l = strophe_snprintf(message, message_len, "p=%s,,n=%s,r=%s",
                              binding_type, node, buf);
     } else {
+        char cb_flag = 'n';
+        const char *dummy_type;
+        size_t dummy_len;
+
+        /* determine if channel binding is supported before advertising it */
+        if (is_secured && tls_init_channel_binding(conn->tls, &dummy_type, &dummy_len) == 0) {
+            cb_flag = 'y';
+        }
+
         l = strophe_snprintf(message, message_len, "%c,,n=%s,r=%s",
-                             is_secured ? 'y' : 'n', node, buf);
+                             cb_flag, node, buf);
     }
     if (l < 0 || (size_t)l >= message_len) {
         goto err_msg;
@@ -820,9 +829,11 @@ static void _auth(xmpp_conn_t *conn)
         scram_ctx->sasl_plus =
             scram_ctx->alg->mask & SASL_MASK_SCRAM_PLUS ? 1 : 0;
         if (_make_scram_init_msg(scram_ctx)) {
+            /* Gracefully drop the unsupported mechanism and try the next */
+            conn->sasl_support &= ~scram_ctx->alg->mask;
             strophe_free(conn->ctx, scram_ctx);
             xmpp_stanza_release(auth);
-            disconnect_mem_error(conn);
+            _auth(conn);
             return;
         }
 

src/tls_schannel.c

@@ -479,7 +479,7 @@ int tls_read(struct conn_interface *intf, void *buff, size_t len)
             int read;
             tls->readybufferpos += bytes;
             newbuff += bytes;
-            read = tls_read(tls, newbuff, len - bytes);
+            read = tls_read(intf, newbuff, len - bytes);
 
             if (read == -1) {
                 if (tls_is_recoverable(intf, tls->lasterror)) {
@@ -553,7 +553,7 @@ int tls_read(struct conn_interface *intf, void *buff, size_t len)
                 tls->recvbufferpos = 0;
             }
 
-            return tls_read(tls, buff, len);
+            return tls_read(intf, buff, len);
         } else if (ret == SEC_E_INCOMPLETE_MESSAGE) {
             tls->lasterror = SEC_E_INCOMPLETE_MESSAGE;
             return -1;
@@ -611,7 +611,7 @@ int tls_write(struct conn_interface *intf, const void *buff, size_t len)
     int sent = 0, ret, remain = len;
     tls_t *tls = intf->conn->tls;
 
-    ret = tls_clear_pending_write(tls);
+    ret = tls_clear_pending_write(intf);
     if (ret <= 0) {
         return ret;
     }
@@ -667,9 +667,9 @@ int tls_write(struct conn_interface *intf, const void *buff, size_t len)
 
         tls->sendbufferpos = 0;
 
-        ret = tls_clear_pending_write(tls);
+        ret = tls_clear_pending_write(intf);
 
-        if (ret == -1 && !tls_is_recoverable(intf, tls_error(tls))) {
+        if (ret == -1 && !tls_is_recoverable(intf, tls_error(intf))) {
             return -1;
         }
 
@@ -682,7 +682,7 @@ int tls_write(struct conn_interface *intf, const void *buff, size_t len)
         }
 
         if (ret == 0 ||
-            (ret == -1 && tls_is_recoverable(intf, tls_error(tls)))) {
+            (ret == -1 && tls_is_recoverable(intf, tls_error(intf)))) {
             return sent;
         }
     }