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>

1 files changed, 49 insertions, 31 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 691660b9b7ef..af399cac5205 100644
--- 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 = {