[PATCH] Check system known_hosts file

["Tomas Trnka" <tomastrnka@xxxxxxx>]

Hello,

this short patch makes libssh check the /etc/ssh/known_hosts file
before the per-user ~/.ssh/known_hosts file, making libssh behave
the same as OpenSSH client.

Tested only on Linux, but it shouldn't influence Windows at all, as
the fopen("/etc/ssh/known_hosts") will always fail and per-user 
configuration will be checked right away. If the superfluous fopen is
a concern, the system known_hosts check can be easily disabled:

#ifndef WIN32
const char *current_knownhosts = "/etc/ssh/ssh_known_hosts";
#else
const char *current_knownhosts = session->knownhosts;
#endif

Signed-off-by: Tomáš Trnka <tomastrnka@xxxxxxx>
--
diff '--exclude=*~' -u -r libssh-0.5.4/src/known_hosts.c libssh-0.5.4-system-known_hosts/src/known_hosts.c
--- libssh-0.5.4/src/known_hosts.c      2013-01-22 11:38:30.000000000 +0100
+++ libssh-0.5.4-system-known_hosts/src/known_hosts.c   2013-03-11 14:20:42.593563301 +0100
@@ -419,6 +419,7 @@
   const char *type;
   int match;
   int ret = SSH_SERVER_NOT_KNOWN;
+  const char *current_knownhosts = "/etc/ssh/ssh_known_hosts";
 
   enter_function();
 
@@ -456,11 +457,22 @@
 
   do {
     tokens = ssh_get_knownhost_line(session, &file,
-        session->knownhosts, &type);
+        current_knownhosts, &type);
 
-    /* End of file, return the current state */
+    /* End of file */
     if (tokens == NULL) {
-      break;
+      /* Checking system known_hosts file done, check user known_hosts now */
+      if (current_knownhosts != session->knownhosts) {
+        current_knownhosts = session->knownhosts;
+        if (file != NULL) {
+          fclose(file);
+        }
+        file = NULL;
+        continue;
+      } else {
+        /* Both files checked, return current state */
+        break;
+      }
     }
     match = match_hashed_host(session, host, tokens[0]);
     if (match == 0){