udhcpc: ignore NAKs from "wrong" servers. Closes 4267

function                                             old     new   delta
udhcpc_main                                         2716    2814     +98

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 24 insertions, 1 deletions

diff --git a/networking/udhcp/dhcpc.c b/networking/udhcp/dhcpc.c
index 25f18b35d..7dfc160e2 100644
--- a/networking/udhcp/dhcpc.c
+++ b/networking/udhcp/dhcpc.c
@@ -1232,7 +1232,7 @@ static void client_background(void)
 int udhcpc_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int udhcpc_main(int argc UNUSED_PARAM, char **argv)
 {
-        uint8_t *temp, *message;
+        uint8_t *message;
         const char *str_V, *str_h, *str_F, *str_r;
         IF_FEATURE_UDHCP_PORT(char *str_P;)
         void *clientid_mac_ptr;
@@ -1640,6 +1640,8 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                 case INIT_SELECTING:
                         /* Must be a DHCPOFFER */
                         if (*message == DHCPOFFER) {
+                                uint8_t *temp;
+
 /* What exactly is server's IP? There are several values.
  * Example DHCP offer captured with tchdump:
  *
@@ -1689,6 +1691,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                         if (*message == DHCPACK) {
                                 uint32_t lease_seconds;
                                 struct in_addr temp_addr;
+                                uint8_t *temp;
 
                                 temp = udhcp_get_option(&packet, DHCP_LEASE_TIME);
                                 if (!temp) {
@@ -1766,6 +1769,26 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                                 continue; /* back to main loop */
                         }
                         if (*message == DHCPNAK) {
+                                /* If network has more than one DHCP server,
+                                 * "wrong" server can reply first, with a NAK.
+                                 * Do not interpret it as a NAK from "our" server.
+                                 */
+                                if (server_addr != 0) {
+                                        uint32_t svid;
+                                        uint8_t *temp;
+
+                                        temp = udhcp_get_option(&packet, DHCP_SERVER_ID);
+                                        if (!temp) {
+ non_matching_svid:
+                                                log1("%s with wrong server ID, ignoring packet",
+                                                        "Received DHCP NAK"
+                                                );
+                                                continue;
+                                        }
+                                        move_from_unaligned32(svid, temp);
+                                        if (svid != server_addr)
+                                                goto non_matching_svid;
+                                }
                                 /* return to init state */
                                 bb_info_msg("Received DHCP NAK");
                                 udhcp_run_script(&packet, "nak");