bug #33634 ip_forward() have a faulty behaviour: Added pbuf flags to mark incoming packets as link-layer broadcast/multicast. Also added code to allow ip_forward() to forward non-broadcast packets to the input netif (set IP_FORWARD_ALLOW_TX_ON_RX_NETIF==1).

src/include/lwip/opt.h

@@ -595,6 +595,17 @@
 #define IP_SOF_BROADCAST_RECV           0
 #endif
 
+/**
+ * IP_FORWARD_ALLOW_TX_ON_RX_NETIF==1: allow ip_forward() to send packets back
+ * out on the netif where it was received. This should only be used for
+ * wireless networks.
+ * ATTENTION: When this is 1, make sure your netif driver correctly marks incoming
+ * link-layer-broadcast/multicast packets as such using the corresponding pbuf flags!
+ */
+#ifndef IP_FORWARD_ALLOW_TX_ON_RX_NETIF
+#define IP_FORWARD_ALLOW_TX_ON_RX_NETIF 0
+#endif
+
 /**
  * LWIP_RANDOMIZE_INITIAL_LOCAL_PORTS==1: randomize the local port for the first
  * local TCP/UDP pcb (default==0). This can prevent creating predictable port
@@ -1821,6 +1832,34 @@
 #define LWIP_CHECKSUM_ON_COPY           0
 #endif
 
+/*
+   ---------------------------------------
+   ---------- Hook options ---------------
+   ---------------------------------------
+*/
+
+/* Hooks are undefined by default, define them to a function if you need them. */
+
+/**
+ * LWIP_HOOK_IP4_INPUT(pbuf, input_netif):
+ * - called from ip_input() (IPv4)
+ * - pbuf: received struct pbuf passed to ip_input()
+ * - input_netif: struct netif on which the packet has been received
+ * Return values:
+ * - 0: Hook has not consumed the packet, packet is processed as normal
+ * - != 0: Hook has consumed the packet.
+ * If the hook consumed the packet, 'pbuf' is in the responsibility of the hook
+ * (i.e. free it when done).
+ */
+
+/**
+ * LWIP_HOOK_IP4_ROUTE(dest):
+ * - called from ip_route() (IPv4)
+ * - dest: destination IPv4 address
+ * Returns the destination netif or NULL if no destination netif is found. In
+ * that case, ip_route() continues as normal.
+ */
+
 /*
    ---------------------------------------
    ---------- Debugging options ----------

src/include/lwip/pbuf.h

@@ -69,6 +69,10 @@ typedef enum {
 #define PBUF_FLAG_IS_CUSTOM 0x02U
 /** indicates this pbuf is UDP multicast to be looped back */
 #define PBUF_FLAG_MCASTLOOP 0x04U
+/** indicates this pbuf was received as link-level broadcast */
+#define PBUF_FLAG_LLBCAST   0x08U
+/** indicates this pbuf was received as link-level multicast */
+#define PBUF_FLAG_LLMCAST   0x10U
 /** indicates this pbuf includes a TCP FIN flag */
 #define PBUF_FLAG_TCP_FIN   0x20U