Implemented hardening against spoofed local-ip packets

As suggested by copilot

Author: danielinux

src/test/unit/unit.c

@@ -1206,6 +1206,51 @@ START_TEST(test_udp_recvfrom_null_addrlen)
 }
 END_TEST
 
+START_TEST(test_udp_recvfrom_src_equals_local_ip_does_not_persist_remote)
+{
+    struct wolfIP s;
+    int sd;
+    struct wolfIP_sockaddr_in sin;
+    uint8_t payload[4] = {0x01, 0x02, 0x03, 0x04};
+    uint8_t rxbuf[4] = {0};
+    struct wolfIP_sockaddr_in from;
+    socklen_t from_len = sizeof(from);
+    int ret;
+    ip4 local_ip = 0x0A000001U;
+    uint16_t local_port = 4005;
+    uint16_t remote_port = 5005;
+    struct tsocket *ts;
+
+    wolfIP_init(&s);
+    mock_link_init(&s);
+    wolfIP_ipconfig_set(&s, local_ip, 0xFFFFFF00U, 0);
+
+    sd = wolfIP_sock_socket(&s, AF_INET, IPSTACK_SOCK_DGRAM, WI_IPPROTO_UDP);
+    ck_assert_int_gt(sd, 0);
+
+    memset(&sin, 0, sizeof(sin));
+    sin.sin_family = AF_INET;
+    sin.sin_port = ee16(local_port);
+    sin.sin_addr.s_addr = ee32(local_ip);
+    ret = wolfIP_sock_bind(&s, sd, (struct wolfIP_sockaddr *)&sin, sizeof(sin));
+    ck_assert_int_eq(ret, 0);
+
+    ts = &s.udpsockets[SOCKET_UNMARK(sd)];
+    ck_assert_uint_eq(ts->remote_ip, 0);
+
+    inject_udp_datagram(&s, TEST_PRIMARY_IF, local_ip, local_ip, remote_port, local_port,
+            payload, sizeof(payload));
+
+    memset(&from, 0, sizeof(from));
+    ret = wolfIP_sock_recvfrom(&s, sd, rxbuf, sizeof(rxbuf), 0,
+            (struct wolfIP_sockaddr *)&from, &from_len);
+    ck_assert_int_eq(ret, (int)sizeof(payload));
+    ck_assert_mem_eq(rxbuf, payload, sizeof(payload));
+    ck_assert_uint_eq(from.sin_addr.s_addr, ee32(local_ip));
+    ck_assert_uint_eq(ts->remote_ip, 0);
+}
+END_TEST
+
 START_TEST(test_sock_error_paths)
 {
     struct wolfIP s;
@@ -12257,6 +12302,8 @@ Suite *wolf_suite(void)
     suite_add_tcase(s, tc_proto);
     tcase_add_test(tc_proto, test_udp_recvfrom_null_addrlen);
     suite_add_tcase(s, tc_proto);
+    tcase_add_test(tc_proto, test_udp_recvfrom_src_equals_local_ip_does_not_persist_remote);
+    suite_add_tcase(s, tc_proto);
     tcase_add_test(tc_proto, test_dns_query_and_callback_a);
     suite_add_tcase(s, tc_proto);
     tcase_add_test(tc_proto, test_dhcp_parse_offer_and_ack);

src/wolfip.c

@@ -2656,8 +2656,11 @@ int wolfIP_sock_recvfrom(struct wolfIP *s, int sockfd, void *buf, size_t len, in
             return -WOLFIP_EAGAIN;
         desc = fifo_peek(&ts->sock.udp.rxbuf);
         udp = (struct wolfIP_udp_datagram *)(ts->rxmem + desc->pos + sizeof(*desc));
-        if (ts->remote_ip == 0)
-            ts->remote_ip = ee32(udp->ip.src);
+        if (ts->remote_ip == 0) {
+            ip4 src_ip = ee32(udp->ip.src);
+            if (src_ip != ts->local_ip)
+                ts->remote_ip = src_ip;
+        }
         if (sin) {
             sin->sin_family = AF_INET;
             sin->sin_port = ee16(udp->src_port);