linux-kernel - [PATCH 3.18 088/108] batman-adv: Avoid WARN on net

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Date:   Mon, 18 Feb 2019 14:44:24 +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,
        syzbot+c764de0fcfadca9a8595@...kaller.appspotmail.com,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Sven Eckelmann <sven@...fation.org>,
        Simon Wunderlich <sw@...onwunderlich.de>
Subject: [PATCH 3.18 088/108] batman-adv: Avoid WARN on net_device without parent in netns

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

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

From: Sven Eckelmann <sven@...fation.org>

commit 955d3411a17f590364238bd0d3329b61f20c1cd2 upstream.

It is not allowed to use WARN* helpers on potential incorrect input from
the user or transient problems because systems configured as panic_on_warn
will reboot due to such a problem.

A NULL return value of __dev_get_by_index can be caused by various problems
which can either be related to the system configuration or problems
(incorrectly returned network namespaces) in other (virtual) net_device
drivers. batman-adv should not cause a (harmful) WARN in this situation and
instead only report it via a simple message.

Fixes: b7eddd0b3950 ("batman-adv: prevent using any virtual device created on batman-adv as hard-interface")
Reported-by: syzbot+c764de0fcfadca9a8595@...kaller.appspotmail.com
Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Sven Eckelmann <sven@...fation.org>
Signed-off-by: Simon Wunderlich <sw@...onwunderlich.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/batman-adv/hard-interface.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -89,8 +89,10 @@ static bool batadv_is_on_batman_iface(co
 	/* recurse over the parent device */
 	parent_dev = __dev_get_by_index(&init_net, net_dev->iflink);
 	/* if we got a NULL parent_dev there is something broken.. */
-	if (WARN(!parent_dev, "Cannot find parent device"))
+	if (!parent_dev) {
+		pr_err("Cannot find parent device\n");
 		return false;
+	}
 
 	ret = batadv_is_on_batman_iface(parent_dev);