ifnet: Detach BPF descriptors on interface vmove event

When an interface is moving to/from a vnet jail, it may still have BPF
descriptors attached. The userland (e.g. tcpdump) does not get noticed
that the interface is departing and still opens BPF descriptors thus
may result in leaking sensitive traffic (e.g. an interface is moved
back to parent jail but a user is still sniffing traffic over it in
the child jail).

Detach BPF descriptors so that the userland will be signaled.

Reviewed by:	ae
MFC after:	3 days
Differential Revision:	https://reviews.freebsd.org/D45727

(cherry picked from commit 1ed9b381d4701fc9f66741256e93b96e22273217)

ifnet: Fix build without BPF

The newly introduced function bpf_ifdetach() is only available when
device bpf is enabled.

Fixes:	1ed9b381d470 ifnet: Detach BPF descriptors on interface vmove event
(cherry picked from commit d8413a1c3ba235a79ae6b8cc35767a861855c7e2)

sys/net/bpf.c

@@ -2849,6 +2849,33 @@ bpf_get_bp_params(struct bpf_if *bp, u_int *bif_dlt, u_int *bif_hdrlen)
 
 	return (0);
 }
+
+/*
+ * Detach descriptors on interface's vmove event.
+ */
+void
+bpf_ifdetach(struct ifnet *ifp)
+{
+	struct bpf_if *bp;
+	struct bpf_d *d;
+
+	BPF_LOCK();
+	CK_LIST_FOREACH(bp, &bpf_iflist, bif_next) {
+		if (bp->bif_ifp != ifp)
+			continue;
+
+		/* Detach common descriptors */
+		while ((d = CK_LIST_FIRST(&bp->bif_dlist)) != NULL) {
+			bpf_detachd_locked(d, true);
+		}
+
+		/* Detach writer-only descriptors */
+		while ((d = CK_LIST_FIRST(&bp->bif_wlist)) != NULL) {
+			bpf_detachd_locked(d, true);
+		}
+	}
+	BPF_UNLOCK();
+}
 #endif
 
 /*

sys/net/bpf.h

@@ -431,6 +431,7 @@ void	bpfdetach(struct ifnet *);
 bool	bpf_peers_present_if(struct ifnet *);
 #ifdef VIMAGE
 int	bpf_get_bp_params(struct bpf_if *, u_int *, u_int *);
+void	bpf_ifdetach(struct ifnet *);
 #endif
 
 void	bpfilterattach(int);

sys/net/if.c

@@ -1266,6 +1266,13 @@ finish_vnet_shutdown:
 static void
 if_vmove(struct ifnet *ifp, struct vnet *new_vnet)
 {
+#ifdef DEV_BPF
+	/*
+	 * Detach BPF file descriptors from its interface.
+	 */
+	bpf_ifdetach(ifp);
+#endif
+
 	/*
 	 * Detach from current vnet, but preserve LLADDR info, do not
 	 * mark as dead etc. so that the ifnet can be reattached later.