During if_detach(), invoke if_dead() to set the ifnet's function

pointers to "dead" implementations that no-op rather than invoking
the device driver.  This would generally be unexpected and
possibly quite badly handled by most device drivers after
if_detach() has completed.

Reviewed by:	bms
MFC after:	3 weeks

sys/conf/files

@@ -2152,6 +2152,7 @@ net/if_arcsubr.c		optional arcnet
 net/if_atmsubr.c		optional atm
 net/if_bridge.c			optional bridge | if_bridge
 net/if_clone.c			standard
+net/if_dead.c			standard
 net/if_disc.c			optional disc
 net/if_edsc.c			optional edsc
 net/if_ef.c			optional ef

sys/net/if.c

@@ -928,6 +928,11 @@ if_detach(struct ifnet *ifp)
 #endif
 	if_purgemaddrs(ifp);
 
+	/*
+	 * Prevent further calls into the device driver via ifnet.
+	 */
+	if_dead(ifp);
+
 	/*
 	 * Remove link ifaddr pointer and maybe decrement if_index.
 	 * Clean up all addresses.

sys/net/if_dead.c

@@ -0,0 +1,114 @@
+/*-
+ * Copyright (c) 2009 Robert N. M. Watson
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+/*
+ * When an interface has been detached but not yet freed, we set the various
+ * ifnet function pointers to "ifdead" versions.  This prevents unexpected
+ * calls from the network stack into the device driver after if_detach() has
+ * returned.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/mbuf.h>
+#include <sys/socket.h>
+
+#include <net/if.h>
+#include <net/if_var.h>
+
+static int
+ifdead_output(struct ifnet *ifp, struct mbuf *m, struct sockaddr *sa,
+    struct route *ro)
+{
+
+	m_freem(m);
+	return (ENXIO);
+}
+
+static void
+ifdead_input(struct ifnet *ifp, struct mbuf *m)
+{
+
+	m_freem(m);
+}
+
+static void
+ifdead_start(struct ifnet *ifp)
+{
+
+}
+
+static int
+ifdead_ioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
+{
+
+	return (ENXIO);
+}
+
+static void
+ifdead_watchdog(struct ifnet *ifp)
+{
+
+}
+
+static int
+ifdead_resolvemulti(struct ifnet *ifp, struct sockaddr **llsa,
+    struct sockaddr *sa)
+{
+
+	*llsa = NULL;
+	return (ENXIO);
+}
+
+static void
+ifdead_qflush(struct ifnet *ifp)
+{
+
+}
+
+static int
+ifdead_transmit(struct ifnet *ifp, struct mbuf *m)
+{
+
+	m_freem(m);
+	return (ENXIO);
+}
+
+void
+if_dead(struct ifnet *ifp)
+{
+
+	ifp->if_output = ifdead_output;
+	ifp->if_input = ifdead_input;
+	ifp->if_start = ifdead_start;
+	ifp->if_ioctl = ifdead_ioctl;
+	ifp->if_watchdog = ifdead_watchdog;
+	ifp->if_resolvemulti = ifdead_resolvemulti;
+	ifp->if_qflush = ifdead_qflush;
+	ifp->if_transmit = ifdead_transmit;
+}

sys/net/if_var.h

@@ -753,6 +753,7 @@ int	if_addmulti(struct ifnet *, struct sockaddr *, struct ifmultiaddr **);
 int	if_allmulti(struct ifnet *, int);
 struct	ifnet* if_alloc(u_char);
 void	if_attach(struct ifnet *);
+void	if_dead(struct ifnet *);
 int	if_delmulti(struct ifnet *, struct sockaddr *);
 void	if_delmulti_ifma(struct ifmultiaddr *);
 void	if_detach(struct ifnet *);