From: Andrew Lunn andrew@lunn.ch

batman-adv checks in different situation if a new device is already on top of a different batman-adv device. This is done by getting the iflink of a device and all its parent. It assumes that this iflink is always a parent device in an acyclic graph. But this assumption is broken by devices like veth which are actually a pair of two devices linked to each other. The recursive check would therefore get veth0 when calling dev_get_iflink on veth1. And it gets veth0 when calling dev_get_iflink with veth1.

Creating a veth pair and loading batman-adv freezes parts of the system

ip link add veth0 type veth peer name veth1 modprobe batman-adv

An RCU stall will be detected on the system which cannot be fixed.

INFO: rcu_sched self-detected stall on CPU 1: (5264 ticks this GP) idle=3e9/140000000000001/0 softirq=144683/144686 fqs=5249 (t=5250 jiffies g=46 c=45 q=43) Task dump for CPU 1: insmod R running task 0 247 245 0x00000008 ffffffff8151f140 ffffffff8107888e ffff88000fd141c0 ffffffff8151f140 0000000000000000 ffffffff81552df0 ffffffff8107b420 0000000000000001 ffff88000e3fa700 ffffffff81540b00 ffffffff8107d667 0000000000000001 Call Trace: <IRQ> [<ffffffff8107888e>] ? rcu_dump_cpu_stacks+0x7e/0xd0 [<ffffffff8107b420>] ? rcu_check_callbacks+0x3f0/0x6b0 [<ffffffff8107d667>] ? hrtimer_run_queues+0x47/0x180 [<ffffffff8107cf9d>] ? update_process_times+0x2d/0x50 [<ffffffff810873fb>] ? tick_handle_periodic+0x1b/0x60 [<ffffffff810290ae>] ? smp_trace_apic_timer_interrupt+0x5e/0x90 [<ffffffff813bbae2>] ? apic_timer_interrupt+0x82/0x90 <EOI> [<ffffffff812c3fd7>] ? __dev_get_by_index+0x37/0x40 [<ffffffffa0031f3e>] ? batadv_hard_if_event+0xee/0x3a0 [batman_adv] [<ffffffff812c5801>] ? register_netdevice_notifier+0x81/0x1a0 [...]

This can be avoided by checking if two devices are each others parent and stopping the check in this situation.

Fixes: 3d48811b27f5 ("batman-adv: prevent using any virtual device created on batman-adv as hard-interface") Signed-off-by: Andrew Lunn andrew@lunn.ch [sven@narfation.org: rewritten description, extracted fix] Signed-off-by: Sven Eckelmann sven@narfation.org --- v2: - fix kernel-doc warning

net/batman-adv/hard-interface.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+)

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c index aea4d06..730cfa8 100644 --- a/net/batman-adv/hard-interface.c +++ b/net/batman-adv/hard-interface.c @@ -79,6 +79,28 @@ out: }

/** + * batadv_mutual_parents - check if two devices are each others parent + * @dev1: 1st net_device + * @dev2: 2nd net_device + * + * veth devices come in pairs and each is the parent of the other! + * + * Return: true if the devices are each others parent, otherwise false + */ +static bool batadv_mutual_parents(const struct net_device *dev1, + const struct net_device *dev2) +{ + int dev1_parent_iflink = dev_get_iflink(dev1); + int dev2_parent_iflink = dev_get_iflink(dev2); + + if (!dev1_parent_iflink || !dev2_parent_iflink) + return false; + + return (dev1_parent_iflink == dev2->ifindex) && + (dev2_parent_iflink == dev1->ifindex); +} + +/** * batadv_is_on_batman_iface - check if a device is a batman iface descendant * @net_dev: the device to check * @@ -111,6 +133,9 @@ static bool batadv_is_on_batman_iface(const struct net_device *net_dev) if (WARN(!parent_dev, "Cannot find parent device")) return false;

+ if (batadv_mutual_parents(net_dev, parent_dev)) + return false; + ret = batadv_is_on_batman_iface(parent_dev);

return ret;