packet: race condition in packet_bind

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 <fruggeri@arista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 691660b9b7effdc59d10517ebf099ca8736efe14..af399cac5205402480300ae7b7d6fbb2094095fb 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2911,22 +2911,40 @@ static int packet_release(struct socket *sock)
  *     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;
@@ -2934,14 +2952,29 @@ static int packet_do_bind(struct sock *sk, struct net_device *dev, __be16 proto)
        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);
@@ -2949,7 +2982,7 @@ static int packet_do_bind(struct sock *sk, struct net_device *dev, __be16 proto)
        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;
@@ -2958,9 +2991,10 @@ static int packet_do_bind(struct sock *sk, struct net_device *dev, __be16 proto)
        }
 
 out_unlock:
+       rcu_read_unlock();
        spin_unlock(&po->bind_lock);
        release_sock(sk);
-       return 0;
+       return ret;
 }
 
 /*
@@ -2972,8 +3006,6 @@ static int packet_bind_spkt(struct socket *sock, struct sockaddr *uaddr,
 {
        struct sock *sk = sock->sk;
        char name[15];
-       struct net_device *dev;
-       int err = -ENODEV;
 
        /*
         *      Check legality
@@ -2983,19 +3015,13 @@ static int packet_bind_spkt(struct socket *sock, struct sockaddr *uaddr,
                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
@@ -3006,16 +3032,8 @@ static int packet_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len
        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 = {