From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Shigeru Yoshida Subject: [PATCH] batman-adv: Fix hang up with small MTU hard-interface Date: Sat, 20 Aug 2022 12:25:16 +0900 Message-Id: <20220820032516.200446-1-syoshida@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="US-ASCII"; x-default=true List-Id: The list for a Better Approach To Mobile Ad-hoc Networking List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: mareklindner@neomailbox.ch, sw@simonwunderlich.de, a@unstable.cc, sven@narfation.org Cc: b.a.t.m.a.n@lists.open-mesh.org, linux-kernel@vger.kernel.org, Shigeru Yoshida 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. Signed-off-by: Shigeru Yoshida --- net/batman-adv/hard-interface.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c index b8f8da7ee3de..dce5557800e9 100644 --- a/net/batman-adv/hard-interface.c +++ b/net/batman-adv/hard-interface.c @@ -700,6 +700,9 @@ 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; -- 2.37.2