Handle truncated DHCP messages, provided only the BOOTP vendor area is

truncated. Fixes [3f10c9b871].

diff --git a/dhcp.c b/dhcp.c
index cb582f9f0fcbb24c83084d23cd7133ffd68dc903..21c1c7109e76166900128d549456457b7dce6fb1 100644 (file)
--- a/dhcp.c
+++ b/dhcp.c
@@ -1084,9 +1084,12 @@ make_message(struct bootp **bootpm, const struct interface *ifp, uint8_t type)
        *p++ = DHO_END;
        len = (size_t)(p - (uint8_t *)bootp);
 
-       /* Pad out to the BOOTP minimum message length.
-        * Some DHCP servers incorrectly require this. */
-       while (len < BOOTP_MESSAGE_LENTH_MIN) {
+       /* Pad out to the BOOTP message length.
+        * Even if we send a DHCP packet with a variable length vendor area,
+        * some servers / relay agents don't like packets smaller than
+        * a BOOTP message which is fine because that's stipulated
+        * in RFC1542 section 2.1. */
+       while (len < sizeof(*bootp)) {
                *p++ = DHO_PAD;
                len++;
        }
@@ -3136,14 +3139,26 @@ dhcp_handlepacket(void *arg)
                            "%s: server %s is not destination",
                            ifp->name, inet_ntoa(from));
                }
-
+               /*
+                * DHCP has a variable option area rather than a fixed
+                * vendor area.
+                * Because DHCP uses the BOOTP protocol it should
+                * still send BOOTP sized packets to be RFC compliant.
+                * However some servers send a truncated vendor area.
+                * dhcpcd can work fine without the vendor area being sent.
+                */
                bytes = get_udp_data(&bootp, buf);
-               if (bytes < sizeof(struct bootp)) {
+               if (bytes < offsetof(struct bootp, vend)) {
                        logger(ifp->ctx, LOG_ERR,
                            "%s: truncated packet (%zu) from %s",
                            ifp->name, bytes, inet_ntoa(from));
                        continue;
                }
+               /* But to make our IS_DHCP macro easy, ensure the vendor
+                * area has at least 4 octets. */
+               while (bytes < offsetof(struct bootp, vend) + 4)
+                       bootp[bytes++] = '\0';
+
                dhcp_handledhcp(ifp, (struct bootp *)bootp, bytes, &from);
                if (state->raw_fd == -1)
                        break;

diff --git a/dhcp.h b/dhcp.h
index 7e90a0ccdccab8b9ccf0b2d61cff50f96f90b46b..e007cb034cd1eca23f8771dad89f5b8142ab3033 100644 (file)
--- a/dhcp.h
+++ b/dhcp.h
@@ -131,9 +131,6 @@ enum FQDN {
        FQDN_BOTH       = 0x31
 };
 
-/* Some crappy DHCP servers require the BOOTP minimum length */
-#define BOOTP_MESSAGE_LENTH_MIN 300
-
 /* Don't import common.h as that defines __unused which causes problems
  * on some Linux systems which define it as part of a structure */
 #if __GNUC__ > 2 || defined(__INTEL_COMPILER)