Patch "packet: race condition in packet_bind" has been added to the 4.3-stable tree

PATCH [email protected] 1 participant 1 message Nov 17, 2015

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2015-11-17 22:43 UTC #0 lore raw

This is a note to let you know that I've just added the patch titled

packet: race condition in packet_bind

to the 4.3-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
packet-race-condition-in-packet_bind.patch
and it can be found in the queue-4.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From foo@baz Tue Nov 17 14:33:46 PST 2015

From: Francesco Ruggeri <[email protected]>
Date: Thu, 5 Nov 2015 08:16:14 -0800
Subject: packet: race condition in packet_bind

From: Francesco Ruggeri <[email protected]>

[ Upstream commit 30f7ea1c2b5f5fb7462c5ae44fe2e40cb2d6a474 ]

There is a race conditions between packet_notifier and packet_bind{_spkt}.

It happens if packet_notifier(NETDEV_UNREGISTER) executes between the time packet_bind{_spkt} takes a reference on the new netdevice and the time packet_do_bind sets po->ifindex.
In this case the notification can be missed.
If this happens during a dev_change_net_namespace this can result in the netdevice to be moved to the new namespace while the packet_sock in the old namespace still holds a reference on it. When the netdevice is later deleted in the new namespace the deletion hangs since the packet_sock is not found in the new namespace' &net->packet.sklist.
It can be reproduced with the script below.

This patch makes packet_do_bind check again for the presence of the netdevice in the packet_sock's namespace after the synchronize_net in unregister_prot_hook.
More in general it also uses the rcu lock for the duration of the bind to stop dev_change_net_namespace/rollback_registered_many from going past the synchronize_net following unlist_netdevice, so that no NETDEV_UNREGISTER notifications can happen on the new netdevice while the bind is executing. In order to do this some code from packet_bind{_spkt} is consolidated into packet_do_dev.

import socket, os, time, sys
proto=7
realDev='em1'
vlanId=400
if len(sys.argv) > 1:
vlanId=int(sys.argv[1])
dev='vlan%d' % vlanId

os.system('taskset -p 0x10 %d' % os.getpid())

s = socket.socket(socket.PF_PACKET, socket.SOCK_RAW, proto) os.system('ip link add link %s name %s type vlan id %d' %
(realDev, dev, vlanId))
os.system('ip netns add dummy')

pid=os.fork()

if pid == 0:

   # dev should be moved while packet_do_bind is in synchronize net
   os.system('taskset -p 0x20000 %d' % os.getpid())
   os.system('ip link set %s netns dummy' % dev)
   os.system('ip netns exec dummy ip link del %s' % dev)
   s.close()
   sys.exit(0)

time.sleep(.004)
try:
s.bind(('%s' % dev, proto+1))
except:
print 'Could not bind socket'
s.close()
os.system('ip netns del dummy')
sys.exit(0)

os.waitpid(pid, 0)
s.close()
os.system('ip netns del dummy')
sys.exit(0)

Signed-off-by Francesco Ruggeri <[email protected]>

Signed-off-by David S. Miller <[email protected]>

Signed-off-by Greg Kroah-Hartman <[email protected]>

---
 net/packet/af_packet.c |   80 ++++++++++++++++++++++++++++++-------------------
 1 file changed, 49 insertions(+), 31 deletions(-)

net/packet/af_packet.c +49 ~~-31~~

@@ -2903,22 +2903,40 @@ static int packet_release(struct socket
  *	Attach a packet hook.
  */
 
-static int packet_do_bind(struct sock *sk, struct net_device *dev, __be16 proto)
+static int packet_do_bind(struct sock *sk, const char *name, int ifindex,
+			  __be16 proto)
 {
 	struct packet_sock *po = pkt_sk(sk);
 	struct net_device *dev_curr;
 	__be16 proto_curr;
 	bool need_rehook;
+	struct net_device *dev = NULL;
+	int ret = 0;
+	bool unlisted = false;
 
-	if (po->fanout) {
-		if (dev)
-			dev_put(dev);
-
+	if (po->fanout)
 		return -EINVAL;
-	}
 
 	lock_sock(sk);
 	spin_lock(&po->bind_lock);
+	rcu_read_lock();
+
+	if (name) {
+		dev = dev_get_by_name_rcu(sock_net(sk), name);
+		if (!dev) {
+			ret = -ENODEV;
+			goto out_unlock;
+		}
+	} else if (ifindex) {
+		dev = dev_get_by_index_rcu(sock_net(sk), ifindex);
+		if (!dev) {
+			ret = -ENODEV;
+			goto out_unlock;
+		}
+	}
+
+	if (dev)
+		dev_hold(dev);
 
 	proto_curr = po->prot_hook.type;
 	dev_curr = po->prot_hook.dev;

@@ -2926,14 +2944,29 @@ static int packet_do_bind(struct sock *s
 	need_rehook = proto_curr != proto || dev_curr != dev;
 
 	if (need_rehook) {
-		unregister_prot_hook(sk, true);
+		if (po->running) {
+			rcu_read_unlock();
+			__unregister_prot_hook(sk, true);
+			rcu_read_lock();
+			dev_curr = po->prot_hook.dev;
+			if (dev)
+				unlisted = !dev_get_by_index_rcu(sock_net(sk),
+								 dev->ifindex);
+		}
 
 		po->num = proto;
 		po->prot_hook.type = proto;
-		po->prot_hook.dev = dev;
 
-		po->ifindex = dev ? dev->ifindex : 0;
-		packet_cached_dev_assign(po, dev);
+		if (unlikely(unlisted)) {
+			dev_put(dev);
+			po->prot_hook.dev = NULL;
+			po->ifindex = -1;
+			packet_cached_dev_reset(po);
+		} else {
+			po->prot_hook.dev = dev;
+			po->ifindex = dev ? dev->ifindex : 0;
+			packet_cached_dev_assign(po, dev);
+		}
 	}
 	if (dev_curr)
 		dev_put(dev_curr);

@@ -2941,7 +2974,7 @@ static int packet_do_bind(struct sock *s
 	if (proto == 0 || !need_rehook)
 		goto out_unlock;
 
-	if (!dev || (dev->flags & IFF_UP)) {
+	if (!unlisted && (!dev || (dev->flags & IFF_UP))) {
 		register_prot_hook(sk);
 	} else {
 		sk->sk_err = ENETDOWN;

@@ -2950,9 +2983,10 @@ static int packet_do_bind(struct sock *s
 	}
 
 out_unlock:
+	rcu_read_unlock();
 	spin_unlock(&po->bind_lock);
 	release_sock(sk);
-	return 0;
+	return ret;
 }
 
 /*

@@ -2964,8 +2998,6 @@ static int packet_bind_spkt(struct socke
 {
 	struct sock *sk = sock->sk;
 	char name[15];
-	struct net_device *dev;
-	int err = -ENODEV;
 
 	/*
 	 *	Check legality

@@ -2975,19 +3007,13 @@ static int packet_bind_spkt(struct socke
 		return -EINVAL;
 	strlcpy(name, uaddr->sa_data, sizeof(name));
 
-	dev = dev_get_by_name(sock_net(sk), name);
-	if (dev)
-		err = packet_do_bind(sk, dev, pkt_sk(sk)->num);
-	return err;
+	return packet_do_bind(sk, name, 0, pkt_sk(sk)->num);
 }
 
 static int packet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 {
 	struct sockaddr_ll *sll = (struct sockaddr_ll *)uaddr;
 	struct sock *sk = sock->sk;
-	struct net_device *dev = NULL;
-	int err;
-
 
 	/*
 	 *	Check legality

@@ -2998,16 +3024,8 @@ static int packet_bind(struct socket *so
 	if (sll->sll_family != AF_PACKET)
 		return -EINVAL;
 
-	if (sll->sll_ifindex) {
-		err = -ENODEV;
-		dev = dev_get_by_index(sock_net(sk), sll->sll_ifindex);
-		if (dev == NULL)
-			goto out;
-	}
-	err = packet_do_bind(sk, dev, sll->sll_protocol ? : pkt_sk(sk)->num);
-
-out:
-	return err;
+	return packet_do_bind(sk, NULL, sll->sll_ifindex,
+			      sll->sll_protocol ? : pkt_sk(sk)->num);
 }
 
 static struct proto packet_proto = {

Patches currently in stable-queue which might be from [email protected] are

queue-4.3/packet-race-condition-in-packet_bind.patch