The following commit has been merged in the batadv/lts/5.15 branch: commit 6ddb16e59a1b08725f9ac0ea4d7f13aee401d974 Author: Shigeru Yoshida syoshida@redhat.com Date: Sat Aug 20 12:25:16 2022 +0900

batman-adv: Fix hang up with small MTU hard-interface

commit b1cb8a71f1eaec4eb77051590f7f561f25b15e32 upstream.

The system hangs up when batman-adv soft-interface is created on hard-interface with small MTU. For example, the following commands create batman-adv soft-interface on dummy interface with zero MTU:

# ip link add name dummy0 type dummy # ip link set mtu 0 dev dummy0 # ip link set up dev dummy0 # ip link add name bat0 type batadv # ip link set dev dummy0 master bat0

These commands cause the system hang up with the following messages:

[ 90.578925][ T6689] batman_adv: bat0: Adding interface: dummy0 [ 90.580884][ T6689] batman_adv: bat0: The MTU of interface dummy0 is too small (0) to handle the transport of batman-adv packets. Packets going over this interface will be fragmented on layer2 which could impact the performance. Setting the MTU to 1560 would solve the problem. [ 90.586264][ T6689] batman_adv: bat0: Interface activated: dummy0 [ 90.590061][ T6689] batman_adv: bat0: Forced to purge local tt entries to fit new maximum fragment MTU (-320) [ 90.595517][ T6689] batman_adv: bat0: Forced to purge local tt entries to fit new maximum fragment MTU (-320) [ 90.598499][ T6689] batman_adv: bat0: Forced to purge local tt entries to fit new maximum fragment MTU (-320)

This patch fixes this issue by returning error when enabling hard-interface with small MTU size.

Fixes: c6c8fea29769 ("net: Add batman-adv meshing protocol") Signed-off-by: Shigeru Yoshida syoshida@redhat.com Signed-off-by: Sven Eckelmann sven@narfation.org Signed-off-by: Simon Wunderlich sw@simonwunderlich.de

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c index 35fadb924849..a2dd1ea826ce 100644 --- a/net/batman-adv/hard-interface.c +++ b/net/batman-adv/hard-interface.c @@ -9,6 +9,7 @@

#include <linux/atomic.h> #include <linux/byteorder/generic.h> +#include <linux/errno.h> #include <linux/gfp.h> #include <linux/if.h> #include <linux/if_arp.h> @@ -698,6 +699,9 @@ int batadv_hardif_enable_interface(struct batadv_hard_iface *hard_iface, int max_header_len = batadv_max_header_len(); int ret;

+ if (hard_iface->net_dev->mtu < ETH_MIN_MTU + max_header_len) + return -EINVAL; + if (hard_iface->if_status != BATADV_IF_NOT_IN_USE) goto out;