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

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

[Eric Dumazet]

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@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: wireguard@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);
 
-- 
2.25.0.265.gbab2e86ba0-goog

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

[Jason A. Donenfeld]

Hi Eric,

On 2/14/20, Eric Dumazet <edumazet@google.com> 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.

Thanks for the patch. However, I solved this slightly differently
yesterday afternoon already:
https://git.zx2c4.com/wireguard-linux/commit/?h=stable&id=06e79ab0d545a20dec1b179fa26841eb0afb1f07
. I've got some additional testing of this to do this afternoon, and
then I'll submit it to the list.

Jason