linux-kernel - [PATCH 4.14 29/52] tun: fix rcu_read_lock imbalance in tun_build

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Date:   Fri, 15 Dec 2017 10:52:06 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Xin Long <lucien.xin@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.14 29/52] tun: fix rcu_read_lock imbalance in tun_build_skb

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Xin Long <lucien.xin@...il.com>


[ Upstream commit 654d573845f35017dc397840fa03610fef3d08b0 ]

rcu_read_lock in tun_build_skb is used to rcu_dereference tun->xdp_prog
safely, rcu_read_unlock should be done in every return path.

Now I could see one place missing it, where it returns NULL in switch-case
XDP_REDIRECT,  another palce using rcu_read_lock wrongly, where it returns
NULL in if (xdp_xmit) chunk.

So fix both in this patch.

Fixes: 761876c857cb ("tap: XDP support")
Signed-off-by: Xin Long <lucien.xin@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/net/tun.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1326,6 +1326,7 @@ static struct sk_buff *tun_build_skb(str
 			err = xdp_do_redirect(tun->dev, &xdp, xdp_prog);
 			if (err)
 				goto err_redirect;
+			rcu_read_unlock();
 			return NULL;
 		case XDP_TX:
 			xdp_xmit = true;
@@ -1358,7 +1359,7 @@ static struct sk_buff *tun_build_skb(str
 	if (xdp_xmit) {
 		skb->dev = tun->dev;
 		generic_xdp_tx(skb, xdp_prog);
-		rcu_read_lock();
+		rcu_read_unlock();
 		return NULL;
 	}