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Subject[PATCH 4.3 017/125] packet: race condition in packet_bind
Date
4.3-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Francesco Ruggeri <fruggeri@aristanetworks.com>

[ 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 <fruggeri@arista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/packet/af_packet.c | 80 ++++++++++++++++++++++++++++++-------------------
1 file changed, 49 insertions(+), 31 deletions(-)

--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -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 = {



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