[PATCH 4.20 49/50] batman-adv: Avoid WARN on net_device without parent in netns

From: Greg Kroah-Hartman
Date: Wed Feb 13 2019 - 13:47:58 EST

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


From: Sven Eckelmann <sven@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Sven Eckelmann <sven@xxxxxxxxxxxxx>
Signed-off-by: Simon Wunderlich <sw@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

net/batman-adv/hard-interface.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -20,7 +20,6 @@
#include "main.h"

#include <linux/atomic.h>
-#include <linux/bug.h>
#include <linux/byteorder/generic.h>
#include <linux/errno.h>
#include <linux/gfp.h>
@@ -179,8 +178,10 @@ static bool batadv_is_on_batman_iface(co
parent_dev = __dev_get_by_index((struct net *)parent_net,
/* 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;
+ }

if (batadv_mutual_parents(net_dev, net, parent_dev, parent_net))
return false;