netdev - [PATCH 06/10] tun: Make tun_net_xmit atomic wrt tun_attach && tun

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Message-ID: <m11vuxlmhn.fsf_-_@fess.ebiederm.org>
Date:	Tue, 20 Jan 2009 13:02:28 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	David Miller <davem@...emloft.net>
Cc:	<netdev@...r.kernel.org>, Max Krasnyansky <maxk@...lcomm.com>,
	Pavel Emelyanov <xemul@...nvz.org>
Subject: [PATCH 06/10] tun: Make tun_net_xmit atomic wrt tun_attach && tun_detach


Currently this small race allows for a packet to be received when we
detach from an tun device and still be enqueued.  Not especially
important but not what the code is trying to do.

Signed-off-by: Eric W. Biederman <ebiederm@...stanetworks.com>
---
 drivers/net/tun.c |   24 +++++++++++++++++-------
 1 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index dfbf586..fa93160 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -115,25 +115,33 @@ static int tun_attach(struct tun_struct *tun, struct file *file)
 {
 	struct tun_file *tfile = file->private_data;
 	const struct cred *cred = current_cred();
+	int err;
 
 	ASSERT_RTNL();
 
-	if (tfile->tun)
-		return -EINVAL;
-
-	if (tun->tfile)
-		return -EBUSY;
-
 	/* Check permissions */
 	if (((tun->owner != -1 && cred->euid != tun->owner) ||
 	     (tun->group != -1 && cred->egid != tun->group)) &&
 		!capable(CAP_NET_ADMIN))
 		return -EPERM;
 
+	netif_tx_lock_bh(tun->dev);
+
+	err = -EINVAL;
+	if (tfile->tun)
+		goto out;
+
+	err = -EBUSY;
+	if (tun->tfile)
+		goto out;
+
+	err = 0;
 	tfile->tun = tun;
 	tun->tfile = tfile;
 
-	return 0;
+out:
+	netif_tx_unlock_bh(tun->dev);
+	return err;
 }
 
 static void __tun_detach(struct tun_struct *tun)
@@ -141,8 +149,10 @@ static void __tun_detach(struct tun_struct *tun)
 	struct tun_file *tfile = tun->tfile;
 
 	/* Detach from net device */
+	netif_tx_lock_bh(tun->dev);
 	tfile->tun = NULL;
 	tun->tfile = NULL;
+	netif_tx_unlock_bh(tun->dev);
 
 	/* Drop read queue */
 	skb_queue_purge(&tun->readq);
-- 
1.5.6.3
--
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