[PATCH 3.8 146/166] packet: fix send path when running with proto == 0

Kamal Mostafa
2014-01-15T21:52:40Z

From: Daniel Borkmann <dborkman@redhat.com>

[ Upstream commit 66e56cd46b93ef407c60adcac62cf33b06119d50 ]

Commit e40526cb20b5 introduced a cached dev pointer, that gets
hooked into register_prot_hook(), __unregister_prot_hook() to
update the device used for the send path.

We need to fix this up, as otherwise this will not work with
sockets created with protocol = 0, plus with sll_protocol = 0
passed via sockaddr_ll when doing the bind.

So instead, assign the pointer directly. The compiler can inline
these helper functions automagically.

While at it, also assume the cached dev fast-path as likely(),
and document this variant of socket creation as it seems it is
not widely used (seems not even the author of TX_RING was aware
of that in his reference example [1]). Tested with reproducer
from e40526cb20b5.

[1] http://wiki.ipxwarzone.com/index.php5?title=Linux_packet_mmap#Example

Fixes: e40526cb20b5 ("packet: fix use after free race in send path when dev is released")
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Tested-by: Salam Noureddine <noureddine@aristanetworks.com>
Tested-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
Documentation/networking/packet_mmap.txt | 10 +++++
net/packet/af_packet.c | 65 ++++++++++++++++++++------------
2 files changed, 50 insertions(+), 25 deletions(-)

diff --git a/Documentation/networking/packet_mmap.txt b/Documentation/networking/packet_mmap.txt
index 94444b1..9bac174 100644
--- a/Documentation/networking/packet_mmap.txt
+++ b/Documentation/networking/packet_mmap.txt
@@ -123,6 +123,16 @@ Transmission process is similar to capture as shown below.
[shutdown] close() --------> destruction of the transmission socket and
deallocation of all associated resources.

+Socket creation and destruction is also straight forward, and is done
+the same way as in capturing described in the previous paragraph:
+
+ int fd = socket(PF_PACKET, mode, 0);
+
+The protocol can optionally be 0 in case we only want to transmit
+via this socket, which avoids an expensive call to packet_rcv().
+In this case, you also need to bind(2) the TX_RING with sll_protocol = 0
+set. Otherwise, htons(ETH_P_ALL) or any other protocol, for example.
+
Binding the socket to your network interface is mandatory (with zero copy) to
know the header size of frames used in the circular buffer.

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 90c1a21..111217c 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -229,6 +229,30 @@ struct packet_skb_cb {
static void __fanout_unlink(struct sock *sk, struct packet_sock *po);
static void __fanout_link(struct sock *sk, struct packet_sock *po);

+static struct net_device *packet_cached_dev_get(struct packet_sock *po)
+{
+ struct net_device *dev;
+
+ rcu_read_lock();
+ dev = rcu_dereference(po->cached_dev);
+ if (likely(dev))
+ dev_hold(dev);
+ rcu_read_unlock();
+
+ return dev;
+}
+
+static void packet_cached_dev_assign(struct packet_sock *po,
+ struct net_device *dev)
+{
+ rcu_assign_pointer(po->cached_dev, dev);
+}
+
+static void packet_cached_dev_reset(struct packet_sock *po)
+{
+ RCU_INIT_POINTER(po->cached_dev, NULL);
+}
+
/* register_prot_hook must be invoked with the po->bind_lock held,
* or from a context in which asynchronous accesses to the packet
* socket is not possible (packet_create()).
@@ -238,12 +262,10 @@ static void register_prot_hook(struct sock *sk)
struct packet_sock *po = pkt_sk(sk);

if (!po->running) {
- if (po->fanout) {
+ if (po->fanout)
__fanout_link(sk, po);
- } else {
+ else
dev_add_pack(&po->prot_hook);
- rcu_assign_pointer(po->cached_dev, po->prot_hook.dev);
- }

sock_hold(sk);
po->running = 1;
@@ -262,12 +284,11 @@ static void __unregister_prot_hook(struct sock *sk, bool sync)
struct packet_sock *po = pkt_sk(sk);

po->running = 0;
- if (po->fanout) {
+
+ if (po->fanout)
__fanout_unlink(sk, po);
- } else {
+ else
__dev_remove_pack(&po->prot_hook);
- RCU_INIT_POINTER(po->cached_dev, NULL);
- }

__sock_put(sk);

@@ -1967,19 +1988,6 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
return tp_len;
}

-static struct net_device *packet_cached_dev_get(struct packet_sock *po)
-{
- struct net_device *dev;
-
- rcu_read_lock();
- dev = rcu_dereference(po->cached_dev);
- if (dev)
- dev_hold(dev);
- rcu_read_unlock();
-
- return dev;
-}
-
static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
{
struct sk_buff *skb;
@@ -1996,7 +2004,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)

mutex_lock(&po->pg_vec_lock);

- if (saddr == NULL) {
+ if (likely(saddr == NULL)) {
dev = packet_cached_dev_get(po);
proto = po->num;
addr = NULL;
@@ -2150,7 +2158,7 @@ static int packet_snd(struct socket *sock,
* Get and verify the address.
*/

- if (saddr == NULL) {
+ if (likely(saddr == NULL)) {
dev = packet_cached_dev_get(po);
proto = po->num;
addr = NULL;
@@ -2358,6 +2366,8 @@ static int packet_release(struct socket *sock)

spin_lock(&po->bind_lock);
unregister_prot_hook(sk, false);
+ packet_cached_dev_reset(po);
+
if (po->prot_hook.dev) {
dev_put(po->prot_hook.dev);
po->prot_hook.dev = NULL;
@@ -2413,14 +2423,17 @@ static int packet_do_bind(struct sock *sk, struct net_device *dev, __be16 protoc

spin_lock(&po->bind_lock);
unregister_prot_hook(sk, true);
+
po->num = protocol;
po->prot_hook.type = protocol;
if (po->prot_hook.dev)
dev_put(po->prot_hook.dev);
- po->prot_hook.dev = dev;

+ po->prot_hook.dev = dev;
po->ifindex = dev ? dev->ifindex : 0;

+ packet_cached_dev_assign(po, dev);
+
if (protocol == 0)
goto out_unlock;

@@ -2533,7 +2546,8 @@ static int packet_create(struct net *net, struct socket *sock, int protocol,
po = pkt_sk(sk);
sk->sk_family = PF_PACKET;
po->num = proto;
- RCU_INIT_POINTER(po->cached_dev, NULL);
+
+ packet_cached_dev_reset(po);

sk->sk_destruct = packet_sock_destruct;
sk_refcnt_debug_inc(sk);
@@ -3290,6 +3304,7 @@ static int packet_notifier(struct notifier_block *this, unsigned long msg, void
sk->sk_error_report(sk);
}
if (msg == NETDEV_UNREGISTER) {
+ packet_cached_dev_reset(po);
po->ifindex = -1;
if (po->prot_hook.dev)
dev_put(po->prot_hook.dev);
--
1.8.3.2