[PATCH 02/21] netlink: Avoid crash with clientless netlink

[Ian Jackson]

In some pathological configurations, it can happen that a packet is
received from the kernel by a netlink which has no clients (that is,
where netlink_inst_reg has not been called).

Don't crash when this happens; instead, print a log message including
the source and destination addresses.

Signed-off-by: Ian Jackson <ijackson at chiark.greenend.org.uk>
---
 debian/changelog |    1 +
 netlink.c        |   13 ++++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/debian/changelog b/debian/changelog
index 5de3542..12b009c 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -3,6 +3,7 @@ secnet (0.3.1~~unstable) unstable; urgency=low
   * Updates to release checklist in Makefile.in.
   * Fix formatting error in secnet.8 manpage.
   * Internal code rearrangements and improvements.
+  * Fix netlink SEGV on clientless netlinks (i.e. configuration error).
 
  --
 
diff --git a/netlink.c b/netlink.c
index 54ad76f..6384c02 100644
--- a/netlink.c
+++ b/netlink.c
@@ -410,12 +410,23 @@ static bool_t netlink_check(struct netlink *st, struct buffer_if *buf,
 }
 
 /* Deliver a packet _to_ client; used after we have decided
- * what to do with it. */
+ * what to do with it (and just to check that the client has
+ * actually registered a delivery function with us). */
 static void netlink_client_deliver(struct netlink *st,
 				   struct netlink_client *client,
 				   uint32_t source, uint32_t dest,
 				   struct buffer_if *buf)
 {
+    if (!client->deliver) {
+	string_t s,d;
+	s=ipaddr_to_string(source);
+	d=ipaddr_to_string(dest);
+	Message(M_ERR,"%s: dropping %s->%s, client not registered\n",
+		st->name,s,d);
+	free(s); free(d);
+	BUF_FREE(buf);
+	return;
+    }
     client->deliver(client->dst, buf);
     client->outcount++;
 }
-- 
1.7.10.4