net/macvtap: fix reference counting

The RCU usage in the original code was broken because
there are cases where we possibly sleep with rcu_read_lock
held. As a fix, change the macvtap_file_get_queue to
get a reference on the socket and the netdev instead of
taking the full rcu_read_lock.

Also, change macvtap_file_get_queue failure case to
not require a subsequent macvtap_file_put_queue, as
pointed out by Ed Swierk.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Ed Swierk <eswierk@aristanetworks.com>
Cc: Sridhar Samudrala <sri@us.ibm.com>
Acked-by: Sridhar Samudrala <sri@us.ibm.com>
Acked-by: Ed Swierk <eswierk@aristanetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 22 insertions, 13 deletions

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index ad1f6ef89308..fe7656bf68c6 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -70,7 +70,8 @@ static struct cdev macvtap_cdev;
  * exists.
  *
  * The callbacks from macvlan are always done with rcu_read_lock held
- * already, while in the file_operations, we get it ourselves.
+ * already. For calls from file_operations, we use the rcu_read_lock_bh
+ * to get a reference count on the socket and the device.
  *
  * When destroying a queue, we remove the pointers from the file and
  * from the dev and then synchronize_rcu to make sure no thread is
@@ -159,13 +160,21 @@ static void macvtap_del_queues(struct net_device *dev)
 
 static inline struct macvtap_queue *macvtap_file_get_queue(struct file *file)
 {
+        struct macvtap_queue *q;
         rcu_read_lock_bh();
-        return rcu_dereference(file->private_data);
+        q = rcu_dereference(file->private_data);
+        if (q) {
+                sock_hold(&q->sk);
+                dev_hold(q->vlan->dev);
+        }
+        rcu_read_unlock_bh();
+        return q;
 }
 
-static inline void macvtap_file_put_queue(void)
+static inline void macvtap_file_put_queue(struct macvtap_queue *q)
 {
-        rcu_read_unlock_bh();
+        sock_put(&q->sk);
+        dev_put(q->vlan->dev);
 }
 
 /*
@@ -314,8 +323,8 @@ static unsigned int macvtap_poll(struct file *file, poll_table * wait)
              sock_writeable(&q->sk)))
                 mask |= POLLOUT | POLLWRNORM;
 
+        macvtap_file_put_queue(q);
 out:
-        macvtap_file_put_queue();
         return mask;
 }
 
@@ -366,8 +375,8 @@ static ssize_t macvtap_aio_write(struct kiocb *iocb, const struct iovec *iv,
 
         result = macvtap_get_user(q, iv, iov_length(iv, count),
                               file->f_flags & O_NONBLOCK);
+        macvtap_file_put_queue(q);
 out:
-        macvtap_file_put_queue();
         return result;
 }
 
@@ -398,10 +407,8 @@ static ssize_t macvtap_aio_read(struct kiocb *iocb, const struct iovec *iv,
         struct sk_buff *skb;
         ssize_t len, ret = 0;
 
-        if (!q) {
-                ret = -ENOLINK;
-                goto out;
-        }
+        if (!q)
+                return -ENOLINK;
 
         len = iov_length(iv, count);
         if (len < 0) {
@@ -437,7 +444,7 @@ static ssize_t macvtap_aio_read(struct kiocb *iocb, const struct iovec *iv,
         remove_wait_queue(q->sk.sk_sleep, &wait);
 
 out:
-        macvtap_file_put_queue();
+        macvtap_file_put_queue(q);
         return ret;
 }
 
@@ -468,7 +475,7 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
                 if (!q)
                         return -ENOLINK;
                 memcpy(devname, q->vlan->dev->name, sizeof(devname));
-                macvtap_file_put_queue();
+                macvtap_file_put_queue(q);
 
                 if (copy_to_user(&ifr->ifr_name, q->vlan->dev->name, IFNAMSIZ) ||
                     put_user((TUN_TAP_DEV | TUN_NO_PI), &ifr->ifr_flags))
@@ -485,8 +492,10 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
                         return -EFAULT;
 
                 q = macvtap_file_get_queue(file);
+                if (!q)
+                        return -ENOLINK;
                 q->sk.sk_sndbuf = u;
-                macvtap_file_put_queue();
+                macvtap_file_put_queue(q);
                 return 0;
 
         case TUNSETOFFLOAD: