* [PATCH net] wireguard: device: provide sane limits for mtu setting
@ 2020-02-14 6:38 Eric Dumazet
2020-02-14 6:40 ` Quan Zhou
2020-02-14 9:11 ` Jason A. Donenfeld
0 siblings, 2 replies; 5+ messages in thread
From: Eric Dumazet @ 2020-02-14 6:38 UTC (permalink / raw)
To: David S . Miller; +Cc: Eric Dumazet, netdev, Eric Dumazet, syzbot, wireguard
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
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH net] wireguard: device: provide sane limits for mtu setting
2020-02-14 6:38 [PATCH net] wireguard: device: provide sane limits for mtu setting Eric Dumazet
@ 2020-02-14 6:40 ` Quan Zhou
2020-02-14 7:11 ` Samir Nassar
2020-02-14 9:11 ` Jason A. Donenfeld
1 sibling, 1 reply; 5+ messages in thread
From: Quan Zhou @ 2020-02-14 6:40 UTC (permalink / raw)
To: wireguard
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@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);
>
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH net] wireguard: device: provide sane limits for mtu setting
2020-02-14 6:40 ` Quan Zhou
@ 2020-02-14 7:11 ` Samir Nassar
2020-02-14 10:11 ` Quan Zhou
0 siblings, 1 reply; 5+ messages in thread
From: Samir Nassar @ 2020-02-14 7:11 UTC (permalink / raw)
To: wireguard
Hello,
from https://github.com/google/syzkaller/blob/master/docs/syzbot.md
"syzbot system continuously fuzzes main Linux kernel branches and automatically reports found bugs to kernel mailing lists."
As I understand it, fuzzing is applying changes to inputs to see what breaks and, in this case, fix it.
It doesn't make sense to set an MTU to 0 so why allow the program to crash on setting the MTU to zero instead of giving back a useful error or preventing the crash in other ways.
Providing dev->min_mtu and dev->max_mtu bounds is a nice thing to do.
Samir
On February 14, 2020 7:40:23 AM GMT+01:00, Quan Zhou <quan@posteo.net> wrote:
>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@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);
>>
>_______________________________________________
>WireGuard mailing list
>WireGuard@lists.zx2c4.com
>https://lists.zx2c4.com/mailman/listinfo/wireguard
--
Samir Nassar
samir@samirnassar.com
Sent from my mobile device. Please excuse my brevity.
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH net] wireguard: device: provide sane limits for mtu setting
2020-02-14 6:38 [PATCH net] wireguard: device: provide sane limits for mtu setting Eric Dumazet
2020-02-14 6:40 ` Quan Zhou
@ 2020-02-14 9:11 ` Jason A. Donenfeld
1 sibling, 0 replies; 5+ messages in thread
From: Jason A. Donenfeld @ 2020-02-14 9:11 UTC (permalink / raw)
To: Eric Dumazet; +Cc: netdev, wireguard, syzbot, David S . Miller, Eric Dumazet
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
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH net] wireguard: device: provide sane limits for mtu setting
2020-02-14 7:11 ` Samir Nassar
@ 2020-02-14 10:11 ` Quan Zhou
0 siblings, 0 replies; 5+ messages in thread
From: Quan Zhou @ 2020-02-14 10:11 UTC (permalink / raw)
To: wireguard
Hi Samir,
I didn't realize this. You convinced me on this one. Thanks!
On 2/14/20 15:11, Samir Nassar wrote:
> Hello,
>
> from https://github.com/google/syzkaller/blob/master/docs/syzbot.md
>
> "syzbot system continuously fuzzes main Linux kernel branches and automatically reports found bugs to kernel mailing lists."
>
> As I understand it, fuzzing is applying changes to inputs to see what breaks and, in this case, fix it.
>
> It doesn't make sense to set an MTU to 0 so why allow the program to crash on setting the MTU to zero instead of giving back a useful error or preventing the crash in other ways.
>
> Providing dev->min_mtu and dev->max_mtu bounds is a nice thing to do.
>
> Samir
>
> On February 14, 2020 7:40:23 AM GMT+01:00, Quan Zhou <quan@posteo.net> wrote:
>> 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@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);
>>>
>> _______________________________________________
>> WireGuard mailing list
>> WireGuard@lists.zx2c4.com
>> https://lists.zx2c4.com/mailman/listinfo/wireguard
_______________________________________________
WireGuard mailing list
WireGuard@lists.zx2c4.com
https://lists.zx2c4.com/mailman/listinfo/wireguard
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2020-02-14 6:38 [PATCH net] wireguard: device: provide sane limits for mtu setting Eric Dumazet
2020-02-14 6:40 ` Quan Zhou
2020-02-14 7:11 ` Samir Nassar
2020-02-14 10:11 ` Quan Zhou
2020-02-14 9:11 ` Jason A. Donenfeld
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