svn commit: r368237 - head/sys/net

[Kristof Provost]

Author: kp
Date: Tue Dec  1 16:23:59 2020
New Revision: 368237
URL: https://svnweb.freebsd.org/changeset/base/368237

Log:
  if: Fix panic when destroying vnet and epair simultaneously
  
  When destroying a vnet and an epair (with one end in the vnet) we often
  panicked. This was the result of the destruction of the epair, which destroys
  both ends simultaneously, happening while vnet_if_return() was moving the
  struct ifnet to its home vnet. This can result in a freed ifnet being re-added
  to the home vnet V_ifnet list. That in turn panics the next time the ifnet is
  used.
  
  Prevent this race by ensuring that vnet_if_return() cannot run at the same time
  as if_detach() or epair_clone_destroy().
  
  PR:		238870, 234985, 244703, 250870
  MFC after:	2 weeks
  Sponsored by:	Modirum MDPay
  Differential Revision:	https://reviews.freebsd.org/D27378

Modified:
  head/sys/net/if.c

Modified: head/sys/net/if.c
==============================================================================
--- head/sys/net/if.c	Tue Dec  1 16:06:31 2020	(r368236)
+++ head/sys/net/if.c	Tue Dec  1 16:23:59 2020	(r368237)
@@ -314,6 +314,9 @@ VNET_DEFINE(struct ifnet **, ifindex_table);
 struct sx ifnet_sxlock;
 SX_SYSINIT_FLAGS(ifnet_sx, &ifnet_sxlock, "ifnet_sx", SX_RECURSE);
 
+struct sx ifnet_detach_sxlock;
+SX_SYSINIT(ifnet_detach, &ifnet_detach_sxlock, "ifnet_detach_sx");
+
 /*
  * The allocation of network interfaces is a rather non-atomic affair; we
  * need to select an index before we are ready to expose the interface for
@@ -543,7 +546,9 @@ vnet_if_return(const void *unused __unused)
 	IFNET_WUNLOCK();
 
 	for (int j = 0; j < i; j++) {
+		sx_xlock(&ifnet_detach_sxlock);
 		if_vmove(pending[j], pending[j]->if_home_vnet);
+		sx_xunlock(&ifnet_detach_sxlock);
 	}
 
 	free(pending, M_IFNET);
@@ -1118,8 +1123,11 @@ if_detach(struct ifnet *ifp)
 
 	CURVNET_SET_QUIET(ifp->if_vnet);
 	found = if_unlink_ifnet(ifp, false);
-	if (found)
+	if (found) {
+		sx_slock(&ifnet_detach_sxlock);
 		if_detach_internal(ifp, 0, NULL);
+		sx_sunlock(&ifnet_detach_sxlock);
+	}
 	CURVNET_RESTORE();
 }
 
@@ -3010,8 +3018,12 @@ ifioctl(struct socket *so, u_long cmd, caddr_t data, s
 		goto out_noref;
 	case SIOCIFDESTROY:
 		error = priv_check(td, PRIV_NET_IFDESTROY);
-		if (error == 0)
+
+		if (error == 0) {
+			sx_slock(&ifnet_detach_sxlock);
 			error = if_clone_destroy(ifr->ifr_name);
+			sx_sunlock(&ifnet_detach_sxlock);
+		}
 		goto out_noref;
 
 	case SIOCIFGCLONERS: