kernel-pfkey: Clear receive buffer before sending request

Many of the messages sent by the kernel, including confirmations to our
requests, are sent as broadcasts to all PF_KEY sockets.  So if an
external tool is used to manage SAs/policies (e.g. unrelated to IPsec)
the receive buffer might be filled, resulting in errors like these:

  error sending to PF_KEY socket: No buffer space available

To avoid this, just clear the buffer before sending any message.

Fixes #3225.

diff --git a/src/libcharon/plugins/kernel_pfkey/kernel_pfkey_ipsec.c b/src/libcharon/plugins/kernel_pfkey/kernel_pfkey_ipsec.c
index 92bbe57..0ae3314 100644 (file)
--- a/src/libcharon/plugins/kernel_pfkey/kernel_pfkey_ipsec.c
+++ b/src/libcharon/plugins/kernel_pfkey/kernel_pfkey_ipsec.c
@@ -1145,6 +1145,23 @@ static status_t pfkey_send_socket(private_kernel_pfkey_ipsec_t *this, int socket
 
        this->mutex_pfkey->lock(this->mutex_pfkey);
 
+       /* the kernel may broadcast messages not related to our requests (e.g. when
+        * managing SAs and policies via an external tool), so let's clear the
+        * receive buffer so there is room for our request and its reply. */
+       while (TRUE)
+       {
+               len = recv(socket, buf, sizeof(buf), MSG_DONTWAIT);
+
+               if (len < 0)
+               {
+                       if (errno == EINTR)
+                       {       /* interrupted, try again */
+                               continue;
+                       }
+                       break;
+               }
+       }
+
        /* FIXME: our usage of sequence numbers is probably wrong. check RFC 2367,
         * in particular the behavior in response to an SADB_ACQUIRE. */
        in->sadb_msg_seq = ++this->seq;