net: core: limit nested device depth

Current code doesn't limit the number of nested devices.
Nested devices would be handled recursively and this needs huge stack
memory. So, unlimited nested devices could make stack overflow.

This patch adds upper_level and lower_level, they are common variables
and represent maximum lower/upper depth.
When upper/lower device is attached or dettached,
{lower/upper}_level are updated. and if maximum depth is bigger than 8,
attach routine fails and returns -EMLINK.

In addition, this patch converts recursive routine of
netdev_walk_all_{lower/upper} to iterator routine.

Test commands:
ip link add dummy0 type dummy
ip link add link dummy0 name vlan1 type vlan id 1
ip link set vlan1 up

for i in {2..55}
do
let A=$i-1

ip link add vlan$i link vlan$A type vlan id $i
done
ip link del dummy0

Splat looks like:
[ 155.513226][ T908] BUG: KASAN: use-after-free in __unwind_start+0x71/0x850
[ 155.514162][ T908] Write of size 88 at addr ffff8880608a6cc0 by task ip/908
[ 155.515048][ T908]
[ 155.515333][ T908] CPU: 0 PID: 908 Comm: ip Not tainted 5.4.0-rc3+ #96
[ 155.516147][ T908] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
[ 155.517233][ T908] Call Trace:
[ 155.517627][ T908]
[ 155.517918][ T908] Allocated by task 0:
[ 155.518412][ T908] (stack is not available)
[ 155.518955][ T908]
[ 155.519228][ T908] Freed by task 0:
[ 155.519885][ T908] (stack is not available)
[ 155.520452][ T908]
[ 155.520729][ T908] The buggy address belongs to the object at ffff8880608a6ac0
[ 155.520729][ T908] which belongs to the cache names_cache of size 4096
[ 155.522387][ T908] The buggy address is located 512 bytes inside of
[ 155.522387][ T908] 4096-byte region [ffff8880608a6ac0, ffff8880608a7ac0)
[ 155.523920][ T908] The buggy address belongs to the page:
[ 155.524552][ T908] page:ffffea0001822800 refcount:1 mapcount:0 mapping:ffff88806c657cc0 index:0x0 compound_mapcount:0
[ 155.525836][ T908] flags: 0x100000000010200(slab|head)
[ 155.526445][ T908] raw: 0100000000010200 ffffea0001813808 ffffea0001a26c08 ffff88806c657cc0
[ 155.527424][ T908] raw: 0000000000000000 0000000000070007 00000001ffffffff 0000000000000000
[ 155.528429][ T908] page dumped because: kasan: bad access detected
[ 155.529158][ T908]
[ 155.529410][ T908] Memory state around the buggy address:
[ 155.530060][ T908] ffff8880608a6b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 155.530971][ T908] ffff8880608a6c00: fb fb fb fb fb f1 f1 f1 f1 00 f2 f2 f2 f3 f3 f3
[ 155.531889][ T908] >ffff8880608a6c80: f3 fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 155.532806][ T908] ^
[ 155.533509][ T908] ffff8880608a6d00: fb fb fb fb fb fb fb fb fb f1 f1 f1 f1 00 00 00
[ 155.534436][ T908] ffff8880608a6d80: f2 f3 f3 f3 f3 fb fb fb 00 00 00 00 00 00 00 00
[ ... ]

Signed-off-by: Taehee Yoo <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/netdevice.h

···
  * 	@perm_addr:		Permanent hw address
  * 	@addr_assign_type:	Hw address assignment type
  * 	@addr_len:		Hardware address length
+ *	@upper_level:		Maximum depth level of upper devices.
+ *	@lower_level:		Maximum depth level of lower devices.
  *	@neigh_priv_len:	Used in neigh_alloc()
  * 	@dev_id:		Used to differentiate devices that share
  * 				the same link layer address
···
 	unsigned char		perm_addr[MAX_ADDR_LEN];
 	unsigned char		addr_assign_type;
 	unsigned char		addr_len;
+	unsigned char		upper_level;
+	unsigned char		lower_level;
 	unsigned short		neigh_priv_len;
 	unsigned short          dev_id;
 	unsigned short          dev_port;

net/core/dev.c

···
 #include "net-sysfs.h"
 
 #define MAX_GRO_SKBS 8
+#define MAX_NEST_DEV 8
 
 /* This should be increased if a protocol with a bigger head is added. */
 #define GRO_MAX_HEAD (MAX_HEADER + 128)
···
 }
 EXPORT_SYMBOL(netdev_upper_get_next_dev_rcu);
 
+static struct net_device *netdev_next_upper_dev(struct net_device *dev,
+						struct list_head **iter)
+{
+	struct netdev_adjacent *upper;
+
+	upper = list_entry((*iter)->next, struct netdev_adjacent, list);
+
+	if (&upper->list == &dev->adj_list.upper)
+		return NULL;
+
+	*iter = &upper->list;
+
+	return upper->dev;
+}
+
 static struct net_device *netdev_next_upper_dev_rcu(struct net_device *dev,
 						    struct list_head **iter)
 {
···
 	return upper->dev;
 }
 
+static int netdev_walk_all_upper_dev(struct net_device *dev,
+				     int (*fn)(struct net_device *dev,
+					       void *data),
+				     void *data)
+{
+	struct net_device *udev, *next, *now, *dev_stack[MAX_NEST_DEV + 1];
+	struct list_head *niter, *iter, *iter_stack[MAX_NEST_DEV + 1];
+	int ret, cur = 0;
+
+	now = dev;
+	iter = &dev->adj_list.upper;
+
+	while (1) {
+		if (now != dev) {
+			ret = fn(now, data);
+			if (ret)
+				return ret;
+		}
+
+		next = NULL;
+		while (1) {
+			udev = netdev_next_upper_dev(now, &iter);
+			if (!udev)
+				break;
+
+			next = udev;
+			niter = &udev->adj_list.upper;
+			dev_stack[cur] = now;
+			iter_stack[cur++] = iter;
+			break;
+		}
+
+		if (!next) {
+			if (!cur)
+				return 0;
+			next = dev_stack[--cur];
+			niter = iter_stack[cur];
+		}
+
+		now = next;
+		iter = niter;
+	}
+
+	return 0;
+}
+
 int netdev_walk_all_upper_dev_rcu(struct net_device *dev,
 				  int (*fn)(struct net_device *dev,
 					    void *data),
 				  void *data)
 {
-	struct net_device *udev;
-	struct list_head *iter;
-	int ret;
+	struct net_device *udev, *next, *now, *dev_stack[MAX_NEST_DEV + 1];
+	struct list_head *niter, *iter, *iter_stack[MAX_NEST_DEV + 1];
+	int ret, cur = 0;
 
-	for (iter = &dev->adj_list.upper,
-	     udev = netdev_next_upper_dev_rcu(dev, &iter);
-	     udev;
-	     udev = netdev_next_upper_dev_rcu(dev, &iter)) {
-		/* first is the upper device itself */
-		ret = fn(udev, data);
-		if (ret)
-			return ret;
+	now = dev;
+	iter = &dev->adj_list.upper;
 
-		/* then look at all of its upper devices */
-		ret = netdev_walk_all_upper_dev_rcu(udev, fn, data);
-		if (ret)
-			return ret;
+	while (1) {
+		if (now != dev) {
+			ret = fn(now, data);
+			if (ret)
+				return ret;
+		}
+
+		next = NULL;
+		while (1) {
+			udev = netdev_next_upper_dev_rcu(now, &iter);
+			if (!udev)
+				break;
+
+			next = udev;
+			niter = &udev->adj_list.upper;
+			dev_stack[cur] = now;
+			iter_stack[cur++] = iter;
+			break;
+		}
+
+		if (!next) {
+			if (!cur)
+				return 0;
+			next = dev_stack[--cur];
+			niter = iter_stack[cur];
+		}
+
+		now = next;
+		iter = niter;
 	}
 
 	return 0;
···
 					void *data),
 			      void *data)
 {
-	struct net_device *ldev;
-	struct list_head *iter;
-	int ret;
+	struct net_device *ldev, *next, *now, *dev_stack[MAX_NEST_DEV + 1];
+	struct list_head *niter, *iter, *iter_stack[MAX_NEST_DEV + 1];
+	int ret, cur = 0;
 
-	for (iter = &dev->adj_list.lower,
-	     ldev = netdev_next_lower_dev(dev, &iter);
-	     ldev;
-	     ldev = netdev_next_lower_dev(dev, &iter)) {
-		/* first is the lower device itself */
-		ret = fn(ldev, data);
-		if (ret)
-			return ret;
+	now = dev;
+	iter = &dev->adj_list.lower;
 
-		/* then look at all of its lower devices */
-		ret = netdev_walk_all_lower_dev(ldev, fn, data);
-		if (ret)
-			return ret;
+	while (1) {
+		if (now != dev) {
+			ret = fn(now, data);
+			if (ret)
+				return ret;
+		}
+
+		next = NULL;
+		while (1) {
+			ldev = netdev_next_lower_dev(now, &iter);
+			if (!ldev)
+				break;
+
+			next = ldev;
+			niter = &ldev->adj_list.lower;
+			dev_stack[cur] = now;
+			iter_stack[cur++] = iter;
+			break;
+		}
+
+		if (!next) {
+			if (!cur)
+				return 0;
+			next = dev_stack[--cur];
+			niter = iter_stack[cur];
+		}
+
+		now = next;
+		iter = niter;
 	}
 
 	return 0;
···
 	return lower->dev;
 }
 
+static u8 __netdev_upper_depth(struct net_device *dev)
+{
+	struct net_device *udev;
+	struct list_head *iter;
+	u8 max_depth = 0;
+
+	for (iter = &dev->adj_list.upper,
+	     udev = netdev_next_upper_dev(dev, &iter);
+	     udev;
+	     udev = netdev_next_upper_dev(dev, &iter)) {
+		if (max_depth < udev->upper_level)
+			max_depth = udev->upper_level;
+	}
+
+	return max_depth;
+}
+
+static u8 __netdev_lower_depth(struct net_device *dev)
+{
+	struct net_device *ldev;
+	struct list_head *iter;
+	u8 max_depth = 0;
+
+	for (iter = &dev->adj_list.lower,
+	     ldev = netdev_next_lower_dev(dev, &iter);
+	     ldev;
+	     ldev = netdev_next_lower_dev(dev, &iter)) {
+		if (max_depth < ldev->lower_level)
+			max_depth = ldev->lower_level;
+	}
+
+	return max_depth;
+}
+
+static int __netdev_update_upper_level(struct net_device *dev, void *data)
+{
+	dev->upper_level = __netdev_upper_depth(dev) + 1;
+	return 0;
+}
+
+static int __netdev_update_lower_level(struct net_device *dev, void *data)
+{
+	dev->lower_level = __netdev_lower_depth(dev) + 1;
+	return 0;
+}
+
 int netdev_walk_all_lower_dev_rcu(struct net_device *dev,
 				  int (*fn)(struct net_device *dev,
 					    void *data),
 				  void *data)
 {
-	struct net_device *ldev;
-	struct list_head *iter;
-	int ret;
+	struct net_device *ldev, *next, *now, *dev_stack[MAX_NEST_DEV + 1];
+	struct list_head *niter, *iter, *iter_stack[MAX_NEST_DEV + 1];
+	int ret, cur = 0;
 
-	for (iter = &dev->adj_list.lower,
-	     ldev = netdev_next_lower_dev_rcu(dev, &iter);
-	     ldev;
-	     ldev = netdev_next_lower_dev_rcu(dev, &iter)) {
-		/* first is the lower device itself */
-		ret = fn(ldev, data);
-		if (ret)
-			return ret;
+	now = dev;
+	iter = &dev->adj_list.lower;
 
-		/* then look at all of its lower devices */
-		ret = netdev_walk_all_lower_dev_rcu(ldev, fn, data);
-		if (ret)
-			return ret;
+	while (1) {
+		if (now != dev) {
+			ret = fn(now, data);
+			if (ret)
+				return ret;
+		}
+
+		next = NULL;
+		while (1) {
+			ldev = netdev_next_lower_dev_rcu(now, &iter);
+			if (!ldev)
+				break;
+
+			next = ldev;
+			niter = &ldev->adj_list.lower;
+			dev_stack[cur] = now;
+			iter_stack[cur++] = iter;
+			break;
+		}
+
+		if (!next) {
+			if (!cur)
+				return 0;
+			next = dev_stack[--cur];
+			niter = iter_stack[cur];
+		}
+
+		now = next;
+		iter = niter;
 	}
 
 	return 0;
···
 	if (netdev_has_upper_dev(upper_dev, dev))
 		return -EBUSY;
 
+	if ((dev->lower_level + upper_dev->upper_level) > MAX_NEST_DEV)
+		return -EMLINK;
+
 	if (!master) {
 		if (netdev_has_upper_dev(dev, upper_dev))
 			return -EEXIST;
···
 	ret = notifier_to_errno(ret);
 	if (ret)
 		goto rollback;
+
+	__netdev_update_upper_level(dev, NULL);
+	netdev_walk_all_lower_dev(dev, __netdev_update_upper_level, NULL);
+
+	__netdev_update_lower_level(upper_dev, NULL);
+	netdev_walk_all_upper_dev(upper_dev, __netdev_update_lower_level, NULL);
 
 	return 0;
 
···
 
 	call_netdevice_notifiers_info(NETDEV_CHANGEUPPER,
 				      &changeupper_info.info);
+
+	__netdev_update_upper_level(dev, NULL);
+	netdev_walk_all_lower_dev(dev, __netdev_update_upper_level, NULL);
+
+	__netdev_update_lower_level(upper_dev, NULL);
+	netdev_walk_all_upper_dev(upper_dev, __netdev_update_lower_level, NULL);
 }
 EXPORT_SYMBOL(netdev_upper_dev_unlink);
 
···
 
 	dev->gso_max_size = GSO_MAX_SIZE;
 	dev->gso_max_segs = GSO_MAX_SEGS;
+	dev->upper_level = 1;
+	dev->lower_level = 1;
 
 	INIT_LIST_HEAD(&dev->napi_list);
 	INIT_LIST_HEAD(&dev->unreg_list);