Fix ng_ksocket(4) operation as a divert socket, which is pretty useful

and has been broken twice:

- in the beginning of div_output() replace KASSERT with assignment, as
  it was in rev. 1.83. [1] [to be MFCed]
- refactor changes introduced in rev. 1.100: do not prepend a new tag
  unconditionally. Before doing this check whether we have one. [2]

A small note for all hacking in this area:
when divert socket is not a real userland, but ng_ksocket(4), we receive
_the same_ mbufs, that we transmitted to socket. These mbufs have rcvif,
the tags we've put on them. And we should treat them correctly.

Discussed with:	mlaier [1]
Silence from:	green [2]
Reviewed by:	maxim
Approved by:	julian (mentor)
MFC after:	1 week

1 files changed, 12 insertions, 11 deletions

diff --git a/sys/netinet/ip_divert.c b/sys/netinet/ip_divert.c
index b391fd252906..8d2b61b07742 100644
--- a/sys/netinet/ip_divert.c
+++ b/sys/netinet/ip_divert.c
@@ -277,21 +277,22 @@ div_output(struct socket *so, struct mbuf *m,
 	struct divert_tag *dt;
 	int error = 0;
 
-	KASSERT(m->m_pkthdr.rcvif == NULL, ("rcvif not null"));
+	m->m_pkthdr.rcvif = NULL;
 
 	if (control)
 		m_freem(control);		/* XXX */
 
-	mtag = m_tag_get(PACKET_TAG_DIVERT,
-			sizeof(struct divert_tag), M_NOWAIT);
-	if (mtag == NULL) {
-		error = ENOBUFS;
-		goto cantsend;
-	}
-	dt = (struct divert_tag *)(mtag+1);
-	dt->info = 0;
-	dt->cookie = 0;
-	m_tag_prepend(m, mtag);
+	if ((mtag = m_tag_find(m, PACKET_TAG_DIVERT, NULL)) == NULL) {
+		mtag = m_tag_get(PACKET_TAG_DIVERT, sizeof(struct divert_tag),
+		    M_NOWAIT | M_ZERO);
+		if (mtag == NULL) {
+			error = ENOBUFS;
+			goto cantsend;
+		}
+		dt = (struct divert_tag *)(mtag+1);
+		m_tag_prepend(m, mtag);
+	} else
+		dt = (struct divert_tag *)(mtag+1);
 
 	/* Loopback avoidance and state recovery */
 	if (sin) {