linux-kernel - Re: [PATCH] batman-adv: Fix hang up with small MTU hard-interface

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Date:   Thu, 08 Sep 2022 01:00:37 +0900 (JST)
From:   Shigeru Yoshida <syoshida@...hat.com>
To:     mareklindner@...mailbox.ch, sw@...onwunderlich.de, a@...table.cc,
        sven@...fation.org
Cc:     b.a.t.m.a.n@...ts.open-mesh.org, linux-kernel@...r.kernel.org,
        syoshida@...hat.com
Subject: Re: [PATCH] batman-adv: Fix hang up with small MTU hard-interface

ping?

On Sat, 20 Aug 2022 12:25:16 +0900, Shigeru Yoshida wrote:
> 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 <syoshida@...hat.com>
> ---
>  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
>