[PATCH 5.19 070/207] batman-adv: Fix hang up with small MTU hard-interface

Greg Kroah-Hartman
2022-09-26T11:46:57Z

From: Shigeru Yoshida <syoshida@redhat.com>

[ Upstream commit b1cb8a71f1eaec4eb77051590f7f561f25b15e32 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/batman-adv/hard-interface.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index b8f8da7ee3de..41c1ad33d009 100644
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -10,6 +10,7 @@
#include <linux/atomic.h>
#include <linux/byteorder/generic.h>
#include <linux/container_of.h>
+#include <linux/errno.h>
#include <linux/gfp.h>
#include <linux/if.h>
#include <linux/if_arp.h>
@@ -700,6 +701,9 @@ 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;

--
2.35.1