packet: fix send path when running with proto == 0

[ 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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 50 insertions, 25 deletions

diff --git a/Documentation/networking/packet_mmap.txt b/Documentation/networking/packet_mmap.txt
index 23dd80e82b8e..0f4376ec8852 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 c503ad6f610f..e8b5a0dfca21 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -237,6 +237,30 @@ 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()).
@@ -246,12 +270,10 @@ 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;
@@ -270,12 +292,11 @@ 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);
 
@@ -2048,19 +2069,6 @@ 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;
@@ -2077,7 +2085,7 @@ 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;
@@ -2231,7 +2239,7 @@ 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;
@@ -2440,6 +2448,8 @@ 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;
@@ -2495,14 +2505,17 @@ 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;
 
@@ -2615,7 +2628,8 @@ 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);
@@ -3369,6 +3383,7 @@ static int packet_notifier(struct notifier_block *this, unsigned long msg, void
                                                 sk->sk_error_report(sk);
                                 }