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: 3d48811b27f5 ("batman-adv: prevent using any virtual device created on batman-adv as hard-interface") Reported-by: syzbot+c764de0fcfadca9a8595@syzkaller.appspotmail.com Reported-by: Dmitry Vyukov dvyukov@google.com Signed-off-by: Sven Eckelmann sven@narfation.org --- Cc: syzbot syzbot+c764de0fcfadca9a8595@syzkaller.appspotmail.com Cc: Dmitry Vyukov dvyukov@google.com Cc: syzkaller-bugs@googlegroups.com --- net/batman-adv/hard-interface.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c index 508f4416..5b7632cf 100644 --- 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(const struct net_device *net_dev) parent_dev = __dev_get_by_index((struct net *)parent_net, dev_get_iflink(net_dev)); /* 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;