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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Sven Eckelmann <sven@narfation.org>,
        Simon Wunderlich <sw@simonwunderlich.de>
Subject: [PATCH 5.10 047/105] batman-adv: Request iflink once in batadv_get_real_netdevice
Date:   Mon,  7 Mar 2022 10:18:50 +0100
Message-Id: <20220307091645.508678672@linuxfoundation.org>
In-Reply-To: <20220307091644.179885033@linuxfoundation.org>
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From: Sven Eckelmann <sven@narfation.org>

commit 6116ba09423f7d140f0460be6a1644dceaad00da upstream.

There is no need to call dev_get_iflink multiple times for the same
net_device in batadv_get_real_netdevice. And since some of the
ndo_get_iflink callbacks are dynamic (for example via RCUs like in
vxcan_get_iflink), it could easily happen that the returned values are not
stable. The pre-checks before __dev_get_by_index are then of course bogus.

Fixes: 5ed4a460a1d3 ("batman-adv: additional checks for virtual interfaces on top of WiFi")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/batman-adv/hard-interface.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -217,14 +217,16 @@ static struct net_device *batadv_get_rea
 	struct net_device *real_netdev = NULL;
 	struct net *real_net;
 	struct net *net;
-	int ifindex;
+	int iflink;
 
 	ASSERT_RTNL();
 
 	if (!netdev)
 		return NULL;
 
-	if (netdev->ifindex == dev_get_iflink(netdev)) {
+	iflink = dev_get_iflink(netdev);
+
+	if (netdev->ifindex == iflink) {
 		dev_hold(netdev);
 		return netdev;
 	}
@@ -234,9 +236,8 @@ static struct net_device *batadv_get_rea
 		goto out;
 
 	net = dev_net(hard_iface->soft_iface);
-	ifindex = dev_get_iflink(netdev);
 	real_net = batadv_getlink_net(netdev, net);
-	real_netdev = dev_get_by_index(real_net, ifindex);
+	real_netdev = dev_get_by_index(real_net, iflink);
 
 out:
 	if (hard_iface)