af-packet: detect MTU mismatch and warn user

If the MTU on the reception interface and the one on the transmission
interface are different, this will result in an error at transmission
when sending packet to the wire.

diff --git a/src/source-af-packet.c b/src/source-af-packet.c
index ec838cbe2eec5fbbda68f9ab28d058da38e2c455..8ceac4a3d700b74bc3d0c8beb89b69727a5e3c00 100644 (file)
--- a/src/source-af-packet.c
+++ b/src/source-af-packet.c
@@ -50,6 +50,7 @@
 #include "util-privs.h"
 #include "util-optimize.h"
 #include "util-checksum.h"
+#include "util-ioctl.h"
 #include "tmqh-packetpool.h"
 #include "source-af-packet.h"
 #include "runmodes.h"
@@ -322,6 +323,7 @@ TmEcode AFPPeersListAdd(AFPThreadVars *ptv)
     SCEnter();
     AFPPeer *peer = SCMalloc(sizeof(AFPPeer));
     AFPPeer *pitem;
+    int mtu, out_mtu;
 
     if (peer == NULL) {
         SCReturnInt(TM_ECODE_FAILED);
@@ -351,6 +353,16 @@ TmEcode AFPPeersListAdd(AFPThreadVars *ptv)
             continue;
         peer->peer = pitem;
         pitem->peer = peer;
+        mtu = GetIfaceMTU(ptv->iface);
+        out_mtu = GetIfaceMTU(ptv->out_iface);
+        if (mtu != out_mtu) {
+            SCLogError(SC_ERR_AFP_CREATE,
+                      "MTU on %s (%d) and %s (%d) are not equal, "
+                      "transmission of packets bigger than %d will fail.",
+                      ptv->iface, mtu,
+                      ptv->out_iface, out_mtu,
+                      (out_mtu > mtu) ? mtu : out_mtu);
+        }
         peerslist.peered += 2;
         break;
     }