[PATCH net] wireguard: device: provide sane limits for mtu setting

[Quan Zhou]

I'm just curious, under what circumstances would people set mtu to zero?

On 2/14/20 14:38, Eric Dumazet wrote:
> If wireguard device mtu is set to zero, a divide by zero
> crash happens in calculate_skb_padding().
>
> This patch provides dev->min_mtu and dev->max_mtu bounds.
>
> Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
> Signed-off-by: Eric Dumazet <edumazet at google.com>
> Reported-by: syzbot <syzkaller at googlegroups.com>
> Cc: Jason A. Donenfeld <Jason at zx2c4.com>
> Cc: wireguard at lists.zx2c4.com
> ---
>   drivers/net/wireguard/device.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/drivers/net/wireguard/device.c b/drivers/net/wireguard/device.c
> index 43db442b1373073eaf5e805cfe6cfee15875437a..c02b84cca122d92ee8a81c5efdcf67aada2554d6 100644
> --- a/drivers/net/wireguard/device.c
> +++ b/drivers/net/wireguard/device.c
> @@ -271,9 +271,14 @@ static void wg_setup(struct net_device *dev)
>   	dev->features |= WG_NETDEV_FEATURES;
>   	dev->hw_features |= WG_NETDEV_FEATURES;
>   	dev->hw_enc_features |= WG_NETDEV_FEATURES;
> +
>   	dev->mtu = ETH_DATA_LEN - MESSAGE_MINIMUM_LENGTH -
>   		   sizeof(struct udphdr) -
>   		   max(sizeof(struct ipv6hdr), sizeof(struct iphdr));
> +	dev->min_mtu = MESSAGE_PADDING_MULTIPLE;
> +	dev->max_mtu = ETH_MAX_MTU - MESSAGE_MINIMUM_LENGTH -
> +		       sizeof(struct udphdr) -
> +		       max(sizeof(struct ipv6hdr), sizeof(struct iphdr));
>   
>   	SET_NETDEV_DEVTYPE(dev, &device_type);
>