Fix SIGSEGV when no best route is found.

In some case there is no a best route, and no source route can be assigned.
This fix set source with the address in the first route found in the route table
or 0.0.0.0 in case an empty route table.

(cherry picked from commit ad9499b)

CHANGELOG.md

@@ -57,6 +57,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Fix gcc-9 and gcc-10 warnings. [#655](https://github.com/greenbone/openvas/pull/655)
 - Fix double free in nasl_cert_query. [#658](https://github.com/greenbone/openvas/pull/658)
 - Fix message to the client if there is a iface problem. [#695](https://github.com/greenbone/openvas/pull/695)
+- Fix SIGSEGV when no best route is found. [#702](https://github.com/greenbone/openvas/pull/702)
 
 ### Removed
 - Remove code from the openvas daemon era. Do not flushall redis. [#689](https://github.com/greenbone/openvas/pull/689)

misc/pcap.c

@@ -1245,13 +1245,26 @@ routethrough (struct in_addr *dest, struct in_addr *source)
             }
         }
     }
+
   /* Set source */
   if (source)
     {
+      /* Source address is given */
       if (src.s_addr != INADDR_ANY)
         source->s_addr = src.s_addr;
-      else
+      /* Source address is INADDR_ANY and there is a good route */
+      else if (best_match != -1)
         source->s_addr = myroutes[best_match].dev->addr.s_addr;
+      /* No best route found and no default */
+      else
+        {
+          /* Assigned first route in the table */
+          if (myroutes[0].dev)
+            source->s_addr = myroutes[0].dev->addr.s_addr;
+          /* or any */
+          else
+            source->s_addr = INADDR_ANY;
+        }
     }
 
   if (best_match != -1)