udhcpd: don't fail ARP check if returned MAC matches client's one

Also, do not unicast replies to yiaddr.

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

1 files changed, 18 insertions, 3 deletions

diff --git a/networking/udhcp/arpping.c b/networking/udhcp/arpping.c
index b10bff651..fa0989d0f 100644
--- a/networking/udhcp/arpping.c
+++ b/networking/udhcp/arpping.c
@@ -41,7 +41,11 @@ enum {
 
 /* Returns 1 if no reply received */
 
-int FAST_FUNC arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, const char *interface)
+int FAST_FUNC arpping(uint32_t test_ip,
+                const uint8_t *safe_mac,
+                uint32_t from_ip,
+                uint8_t *from_mac,
+                const char *interface)
 {
         int timeout_ms;
         struct pollfd pfd[1];
@@ -73,7 +77,7 @@ int FAST_FUNC arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, con
         arp.operation = htons(ARPOP_REQUEST);           /* ARP op code */
         memcpy(arp.sHaddr, from_mac, 6);                /* source hardware address */
         memcpy(arp.sInaddr, &from_ip, sizeof(from_ip)); /* source IP address */
-        /* tHaddr is zero-fiiled */                     /* target hardware address */
+        /* tHaddr is zero-filled */                     /* target hardware address */
         memcpy(arp.tInaddr, &test_ip, sizeof(test_ip)); /* target IP address */
 
         memset(&addr, 0, sizeof(addr));
@@ -98,13 +102,24 @@ int FAST_FUNC arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, con
                         r = read(s, &arp, sizeof(arp));
                         if (r < 0)
                                 break;
+
+                        //bb_error_msg("sHaddr %02x:%02x:%02x:%02x:%02x:%02x",
+                        //      arp.sHaddr[0], arp.sHaddr[1], arp.sHaddr[2],
+                        //      arp.sHaddr[3], arp.sHaddr[4], arp.sHaddr[5]);
+
                         if (r >= ARP_MSG_SIZE
                          && arp.operation == htons(ARPOP_REPLY)
                          /* don't check it: Linux doesn't return proper tHaddr (fixed in 2.6.24?) */
                          /* && memcmp(arp.tHaddr, from_mac, 6) == 0 */
                          && *((uint32_t *) arp.sInaddr) == test_ip
                         ) {
-                                rv = 0;
+                                 /* if ARP source MAC matches safe_mac
+                                  * (which is client's MAC), then it's not a conflict
+                                  * (client simply already has this IP and replies to ARPs!)
+                                  */
+                                if (!safe_mac || memcmp(safe_mac, arp.sHaddr, 6) != 0)
+                                        rv = 0;
+                                //else bb_error_msg("sHaddr == safe_mac");
                                 break;
                         }
                 }