Re: [Patch net v3] tun: fix a memory leak for tfile->tx_array

tfile->tun could be detached before we close the tun fd,
via tun_detach_all(), so it should not be used to check for
tfile->tx_array.

As Jason suggested, we probably have to clean it up
unconditionally both in __tun_deatch() and tun_detach_all(),
but this requires to check if it is initialized or not.
Currently skb_array_cleanup() doesn't have such a check,
so I check it in the caller and introduce a helper function,
it is a bit ugly but we can always improve it in net-next.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Fixes: 1576d9860599 ("tun: switch to use skb array for tx")
Cc: Jason Wang <redacted>
Signed-off-by: Cong Wang <redacted>
---
  drivers/net/tun.c | 15 +++++++++++++--
  1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 4f4a842a1c9c..a8ec589d1359 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c

@@ -611,6 +611,14 @@ static void tun_queue_purge(struct tun_file *tfile)
  	skb_queue_purge(&tfile->sk.sk_error_queue);
  }
  
+static void tun_cleanup_tx_array(struct tun_file *tfile)
+{
+	if (tfile->tx_array.ring.queue) {
+		skb_array_cleanup(&tfile->tx_array);
+		memset(&tfile->tx_array, 0, sizeof(tfile->tx_array));
+	}
+}
+
  static void __tun_detach(struct tun_file *tfile, bool clean)
  {
  	struct tun_file *ntfile;

@@ -657,8 +665,7 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
  			    tun->dev->reg_state == NETREG_REGISTERED)
  				unregister_netdevice(tun->dev);
  		}
-		if (tun)
-			skb_array_cleanup(&tfile->tx_array);
+		tun_cleanup_tx_array(tfile);
  		sock_put(&tfile->sk);
  	}
  }

@@ -700,11 +707,13 @@ static void tun_detach_all(struct net_device *dev)
  		/* Drop read queue */
  		tun_queue_purge(tfile);
  		sock_put(&tfile->sk);
+		tun_cleanup_tx_array(tfile);
  	}
  	list_for_each_entry_safe(tfile, tmp, &tun->disabled, next) {
  		tun_enable_queue(tfile);
  		tun_queue_purge(tfile);
  		sock_put(&tfile->sk);
+		tun_cleanup_tx_array(tfile);
  	}
  	BUG_ON(tun->numdisabled != 0);
  

@@ -2851,6 +2860,8 @@ static int tun_chr_open(struct inode *inode, struct file * file)
  
  	sock_set_flag(&tfile->sk, SOCK_ZEROCOPY);
  
+	memset(&tfile->tx_array, 0, sizeof(tfile->tx_array));
+
  	return 0;
  }