Fix use-after-free bugs in pfsync(4)

Use after free happens for state that is deleted. The reference
count is what prevents the state from being freed. When the
state is dequeued, the reference count is dropped and the memory
freed. We can't dereference the next pointer or re-queue the
state.

MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D8671

1 files changed, 7 insertions, 2 deletions

diff --git a/sys/netpfil/pf/if_pfsync.c b/sys/netpfil/pf/if_pfsync.c
index de6494eec015..0d117d775beb 100644
--- a/sys/netpfil/pf/if_pfsync.c
+++ b/sys/netpfil/pf/if_pfsync.c
@@ -1509,7 +1509,7 @@ pfsync_sendout(int schedswi)
 	struct ip *ip;
 	struct pfsync_header *ph;
 	struct pfsync_subheader *subh;
-	struct pf_state *st;
+	struct pf_state *st, *st_next;
 	struct pfsync_upd_req_item *ur;
 	int offset;
 	int q, count = 0;
@@ -1559,7 +1559,7 @@ pfsync_sendout(int schedswi)
 		offset += sizeof(*subh);
 
 		count = 0;
-		TAILQ_FOREACH(st, &sc->sc_qs[q], sync_list) {
+		TAILQ_FOREACH_SAFE(st, &sc->sc_qs[q], sync_list, st_next) {
 			KASSERT(st->sync_state == q,
 				("%s: st->sync_state == q",
 					__func__));
@@ -1931,6 +1931,8 @@ pfsync_delete_state(struct pf_state *st)
 	if (sc->sc_len == PFSYNC_MINPKT)
 		callout_reset(&sc->sc_tmo, 1 * hz, pfsync_timeout, V_pfsyncif);
 
+	pf_ref_state(st);
+
 	switch (st->sync_state) {
 	case PFSYNC_S_INS:
 		/* We never got to tell the world so just forget about it. */
@@ -1950,6 +1952,9 @@ pfsync_delete_state(struct pf_state *st)
 	default:
 		panic("%s: unexpected sync state %d", __func__, st->sync_state);
 	}
+
+	pf_release_state(st);
+
 	PFSYNC_UNLOCK(sc);
 }