BPF: Don't use magic in buffer length assignments

Define frame header lengths and frame size maximums.
Use this to calculate required buffer sizes.

3 files changed, 9 insertions, 3 deletions

diff --git a/src/arp.c b/src/arp.c
index 2460a1a3..6e3d634a 100644
--- a/src/arp.c
+++ b/src/arp.c
@@ -55,8 +55,9 @@
 #include "logerr.h"
 
 #if defined(ARP)
-#define ARP_LEN								      \
-	(sizeof(struct arphdr) + (2 * sizeof(uint32_t)) + (2 * HWADDR_LEN))
+#define ARP_LEN								\
+	(FRAMEHDRLEN_MAX +						\
+	 sizeof(struct arphdr) + (2 * sizeof(uint32_t)) + (2 * HWADDR_LEN))
 
 /* ARP debugging can be quite noisy. Enable this for more noise! */
 //#define	ARP_DEBUG
diff --git a/src/dhcp.c b/src/dhcp.c
index 2b1e44f1..d5cb7305 100644
--- a/src/dhcp.c
+++ b/src/dhcp.c
@@ -3432,7 +3432,7 @@ static void
 dhcp_readbpf(void *arg)
 {
 	struct interface *ifp = arg;
-	uint8_t buf[10240];	/* Max jumbo frame and some extra */
+	uint8_t buf[FRAMELEN_MAX];
 	ssize_t bytes;
 	struct dhcp_state *state = D_STATE(ifp);
 	ssize_t fl = (ssize_t)bpf_frame_header_len(ifp);
diff --git a/src/if.h b/src/if.h
index cc62cc94..cd24726b 100644
--- a/src/if.h
+++ b/src/if.h
@@ -81,6 +81,11 @@
 #  define ARPHRD_INFINIBAND		32
 #endif
 
+/* Maximum frame length.
+ * Support jumbo frames and some extra. */
+#define	FRAMEHDRLEN_MAX			14	/* only ethernet support */
+#define	FRAMELEN_MAX			(FRAMEHDRLEN_MAX + 9216)
+
 /* Work out if we have a private address or not
  * 10/8
  * 172.16/12