various dst_ifdown routines to catch refcounting bugs

PATCH In review Denis V. Lunev 3 participants 3 messages Sep 27, 2007

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Networking Network drivers IPv4/IPv6 Networking IPsec

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Denis V. Lunev

author

2007-09-27 13:46 UTC #0 lore raw

PATCH 1/1 various dst_ifdown routines to catch refcounting bugs

Moving dst entries into init_net.loopback_dev is not a good thing. This hides obvious and non-obvious ref-counting bugs.

This patch uses net_ns loopback instead of init_net loopback. This allowes to catch various bugs like recent one in IPv6 DAD handling.

Signed-off-by Denis V. Lunev <[email protected]>

net/core/dst.c renamed from net/core/dst.c.loop +2 -2

@@ -279,11 +279,11 @@ static inline void dst_ifdown(struct dst
 	if (!unregister) {
 		dst->input = dst->output = dst_discard;
 	} else {
-		dst->dev = init_net.loopback_dev;
+		dst->dev = dst->dev->nd_net->loopback_dev;
 		dev_hold(dst->dev);
 		dev_put(dev);
 		if (dst->neighbour && dst->neighbour->dev == dev) {
-			dst->neighbour->dev = init_net.loopback_dev;
+			dst->neighbour->dev = dst->dev;
 			dev_put(dev);
 			dev_hold(dst->neighbour->dev);
 		}

net/ipv4/route.c renamed from net/ipv4/route.c.loop +3 -2

@@ -1402,8 +1402,9 @@ static void ipv4_dst_ifdown(struct dst_e
 {
 	struct rtable *rt = (struct rtable *) dst;
 	struct in_device *idev = rt->idev;
-	if (dev != init_net.loopback_dev && idev && idev->dev == dev) {
-		struct in_device *loopback_idev = in_dev_get(init_net.loopback_dev);
+	if (dev != dev->nd_net->loopback_dev && idev && idev->dev == dev) {
+		struct in_device *loopback_idev =
+			in_dev_get(dev->nd_net->loopback_dev);
 		if (loopback_idev) {
 			rt->idev = loopback_idev;
 			in_dev_put(idev);

net/ipv4/xfrm4_policy.c renamed from net/ipv4/xfrm4_policy.c.loop +2 -1

@@ -306,7 +306,8 @@ static void xfrm4_dst_ifdown(struct dst_
 
 	xdst = (struct xfrm_dst *)dst;
 	if (xdst->u.rt.idev->dev == dev) {
-		struct in_device *loopback_idev = in_dev_get(init_net.loopback_dev);
+		struct in_device *loopback_idev =
+			in_dev_get(dev->nd_net->loopback_dev);
 		BUG_ON(!loopback_idev);
 
 		do {

net/ipv6/route.c renamed from net/ipv6/route.c.loop +9 -6

@@ -220,9 +220,12 @@ static void ip6_dst_ifdown(struct dst_en
 {
 	struct rt6_info *rt = (struct rt6_info *)dst;
 	struct inet6_dev *idev = rt->rt6i_idev;
+	struct net_device *loopback_dev =
+		dev->nd_net->loopback_dev;
 
-	if (dev != init_net.loopback_dev && idev != NULL && idev->dev == dev) {
-		struct inet6_dev *loopback_idev = in6_dev_get(init_net.loopback_dev);
+	if (dev != loopback_dev && idev != NULL && idev->dev == dev) {
+		struct inet6_dev *loopback_idev =
+			in6_dev_get(loopback_dev);
 		if (loopback_idev != NULL) {
 			rt->rt6i_idev = loopback_idev;
 			in6_dev_put(idev);

@@ -1185,12 +1188,12 @@ int ip6_route_add(struct fib6_config *cf
 	if ((cfg->fc_flags & RTF_REJECT) ||
 	    (dev && (dev->flags&IFF_LOOPBACK) && !(addr_type&IPV6_ADDR_LOOPBACK))) {
 		/* hold loopback dev/idev if we haven't done so. */
-		if (dev != init_net.loopback_dev) {
+		if (dev != dev->nd_net->loopback_dev) {
 			if (dev) {
 				dev_put(dev);
 				in6_dev_put(idev);
 			}
-			dev = init_net.loopback_dev;
+			dev = dev->nd_net->loopback_dev;
 			dev_hold(dev);
 			idev = in6_dev_get(dev);
 			if (!idev) {

@@ -1894,13 +1897,13 @@ struct rt6_info *addrconf_dst_alloc(stru
 	if (rt == NULL)
 		return ERR_PTR(-ENOMEM);
 
-	dev_hold(init_net.loopback_dev);
+	dev_hold(idev->dev->nd_net->loopback_dev);
 	in6_dev_hold(idev);
 
 	rt->u.dst.flags = DST_HOST;
 	rt->u.dst.input = ip6_input;
 	rt->u.dst.output = ip6_output;
-	rt->rt6i_dev = init_net.loopback_dev;
+	rt->rt6i_dev = idev->dev->nd_net->loopback_dev;
 	rt->rt6i_idev = idev;
 	rt->u.dst.metrics[RTAX_MTU-1] = ipv6_get_mtu(rt->rt6i_dev);
 	rt->u.dst.metrics[RTAX_ADVMSS-1] = ipv6_advmss(dst_mtu(&rt->u.dst));

net/ipv6/xfrm6_policy.c renamed from net/ipv6/xfrm6_policy.c.loop +2 -1

@@ -375,7 +375,8 @@ static void xfrm6_dst_ifdown(struct dst_
 
 	xdst = (struct xfrm_dst *)dst;
 	if (xdst->u.rt6.rt6i_idev->dev == dev) {
-		struct inet6_dev *loopback_idev = in6_dev_get(init_net.loopback_dev);
+		struct inet6_dev *loopback_idev =
+			in6_dev_get(dev->nd_net->loopback_dev);
 		BUG_ON(!loopback_idev);
 
 		do {

net/xfrm/xfrm_policy.c renamed from net/xfrm/xfrm_policy.c.loop +1 -1

@@ -1949,7 +1949,7 @@ static int stale_bundle(struct dst_entry
 void xfrm_dst_ifdown(struct dst_entry *dst, struct net_device *dev)
 {
 	while ((dst = dst->child) && dst->xfrm && dst->dev == dev) {
-		dst->dev = init_net.loopback_dev;
+		dst->dev = dev->nd_net->loopback_dev;
 		dev_hold(dst->dev);
 		dev_put(dev);
 	}

Eric W. Biederman

Acked-by on v1 1/1

2007-09-27 16:27 UTC #1 lore raw

Quoted 2 lines · Denis V. Lunev

Moving dst entries into init_net.loopback_dev is not a good thing. This hides obvious and non-obvious ref-counting bugs.

Acked-by "Eric W. Biederman" <[email protected]>

To be clear using init_net.loopback is currently safe because we don't have any destination cache entries for anything except the initial network namespace.

I have not yet made this change simply because I haven't gotten around to this part in my patches.

I do have a question I would like to bring up, because I like avoiding explicit references to loopback_dev when I can.

/* Dirty hack. We did it in 2.2 (in __dst_free),
* we have _very_ good reasons not to repeat
* this mistake in 2.3, but we have no choice
* now. _It_ _is_ _explicit_ _deliberate_
* _race_ _condition_.
*
* Commented and originally written by Alexey.
*/

What is the race that is talked about in that comment. Can we just assign NULL instead of the loopback device when we bring a route down. My gut feeling is that something like:

	dst->input = dst->output = dst_discard;

may be enough. But I don't know where the deliberate race is.

I haven't traced this all of the way through but from the obvious parts I just get this nagging feeling that something isn't quite right.

Eric

David Miller

maintainer

2007-09-27 19:44 UTC #2 lore raw

From: [email protected] (Eric W. Biederman)
Date: Thu, 27 Sep 2007 10:27:43 -0600

Quoted 6 lines

Quoted 2 lines · Denis V. Lunev
Moving dst entries into init_net.loopback_dev is not a good thing. This hides obvious and non-obvious ref-counting bugs.
Acked-by "Eric W. Biederman" <[email protected]>

Patch applied.

Quoted 12 lines

I do have a question I would like to bring up, because I like avoiding explicit references to loopback_dev when I can.
/* Dirty hack. We did it in 2.2 (in __dst_free),
* we have _very_ good reasons not to repeat
* this mistake in 2.3, but we have no choice
* now. _It_ _is_ _explicit_ _deliberate_
* _race_ _condition_.
*
* Commented and originally written by Alexey.
*/

Quoted 5 lines

What is the race that is talked about in that comment. Can we just assign NULL instead of the loopback device when we bring a route down. My gut feeling is that something like:
	dst->input = dst->output = dst_discard;
may be enough. But I don't know where the deliberate race is.

The packet output path accesses the cached route device asynchronously, and we are resetting the device to be loopback without any synchronization whatsoever. None is in fact possible, and we don't want to add it because that would be way too expensive.

So another thread on the system can either see the original device or the loopback one.

It all works out because as the device goes down we'll purge any packets queued into the transmit queue and packet scheduler for that device.