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packet: race condition in packet_bind

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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>
This commit is contained in:
Francesco Ruggeri 2015-11-05 08:16:14 -08:00 committed by David S. Miller
parent f668f5f7e0
commit 30f7ea1c2b
1 changed files with 49 additions and 31 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

80
net/packet/af_packet.c
View file

@ -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 = {