Fix panic when adding vtnet interfaces to a bridge

vtnet interfaces are always in promiscuous mode (at least if the
VIRTIO_NET_F_CTRL_RX feature is not negotiated with the host).  if_promisc() on
a vtnet interface returned ENOTSUP although it has IFF_PROMISC set. This
confused the bridge code. Instead we now accept all enable/disable promiscuous
commands (and always keep IFF_PROMISC set).

There are also two issues with the if_bridge error handling.

If if_promisc() fails it uses bridge_delete_member() to clean up. This tries to
disable promiscuous mode on the interface. That runs into an assert, because
promiscuous mode was never set in the first place. (That's the panic reported in
PR 200210.)
We can only unset promiscuous mode if the interface actually is promiscuous.
This goes against the reference counting done by if_promisc(), but only the
first/last if_promic() calls can actually fail, so this is safe.

A second issue is a double free of bif. It's already freed by
bridge_delete_member().

PR:		200210
Differential Revision:	https://reviews.freebsd.org/D2804
Reviewed by:	philip (mentor)

1 files changed, 6 insertions, 5 deletions

diff --git a/sys/net/if_bridge.c b/sys/net/if_bridge.c
index faa7681d8878..c6bcfdf80fe0 100644
--- a/sys/net/if_bridge.c
+++ b/sys/net/if_bridge.c
@@ -1033,9 +1033,12 @@ bridge_delete_member(struct bridge_softc *sc, struct bridge_iflist *bif,
 		case IFT_ETHER:
 		case IFT_L2VLAN:
 			/*
-			 * Take the interface out of promiscuous mode.
+			 * Take the interface out of promiscuous mode, but only
+			 * if it was promiscuous in the first place. It might
+			 * not be if we're in the bridge_ioctl_add() error path.
 			 */
-			(void) ifpromisc(ifs, 0);
+			if (ifs->if_flags & IFF_PROMISC)
+				(void) ifpromisc(ifs, 0);
 			break;
 
 		case IFT_GIF:
@@ -1203,10 +1206,8 @@ bridge_ioctl_add(struct bridge_softc *sc, void *arg)
 			break;
 	}
 
-	if (error) {
+	if (error)
 		bridge_delete_member(sc, bif, 0);
-		free(bif, M_DEVBUF);
-	}
 	return (error);
 }