[UNIX]: The unix_nr_socks limit can be exceeded

The unix_nr_socks value is limited with the 2 * get_max_files() value,
as seen from the unix_create1(). However, the check and the actual
increment are separated with the GFP_KERNEL allocation, so this limit
can be exceeded under a memory pressure - task may go to sleep freeing
the pages and some other task will be allowed to allocate a new sock
and so on and so forth.

So make the increment before the check (similar thing is done in the
sock_kmalloc) and go to kmalloc after this.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 3 deletions

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index ab9048ac197..e835da8fc09 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -599,15 +599,14 @@ static struct sock * unix_create1(struct net *net, struct socket *sock)
         struct sock *sk = NULL;
         struct unix_sock *u;
 
-        if (atomic_read(&unix_nr_socks) >= 2*get_max_files())
+        atomic_inc(&unix_nr_socks);
+        if (atomic_read(&unix_nr_socks) > 2 * get_max_files())
                 goto out;
 
         sk = sk_alloc(net, PF_UNIX, GFP_KERNEL, &unix_proto);
         if (!sk)
                 goto out;
 
-        atomic_inc(&unix_nr_socks);
-
         sock_init_data(sock,sk);
         lockdep_set_class(&sk->sk_receive_queue.lock,
                                 &af_unix_sk_receive_queue_lock_key);
@@ -625,6 +624,8 @@ static struct sock * unix_create1(struct net *net, struct socket *sock)
         init_waitqueue_head(&u->peer_wait);
         unix_insert_socket(unix_sockets_unbound, sk);
 out:
+        if (sk == NULL)
+                atomic_dec(&unix_nr_socks);
         return sk;
 }