From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: Roman Mamedov <rm.wg@romanrm.net>
Cc: Luis Ressel <aranea@aixah.de>,
WireGuard mailing list <wireguard@lists.zx2c4.com>
Subject: Re: Mixed MTU hosts on a network
Date: Sat, 14 Apr 2018 04:40:21 +0200 [thread overview]
Message-ID: <20180414024017.GA14470@zx2c4.com> (raw)
In-Reply-To: <CAHmME9rVba9Zzv65guftwxZcRGWBY0uaP=_GhHVnBz=8+L6Y3A@mail.gmail.com>
On Sat, Apr 14, 2018 at 03:38:46AM +0200, Jason A. Donenfeld wrote:
> 2) When we pad the packet payload. In this case, we pad it to the
> nearest multiple of 16, but we don't let it exceed the device MTU.
> This is skb_padding in send.c. This behavior seems like the bug in
> your particular case, since what matters here is the route's MTU, not
> the device MTU. For full 1412 size packets, the payload is presumably
> being padded to 1424, since that's still less than the device MTU. In
> order to test this theory, try setting your route MTU, as you've
> described in your first email, to 1408 (which is a multiple of 16). If
> this works, let me know, as it will be good motivation for fixing
> skb_padding. If not, then it means there's a problem elsewhere to
> investigate too.
>
> I'm CC'ing Luis on this email, as he was working on the MTU code a while back.
I'm still playing with this, but something like the following might fix
the issue, if you're interested in playing a bit.
=~=~=~=~=~=~=
diff --git a/src/device.c b/src/device.c
index 1614d61..3d18368 100644
--- a/src/device.c
+++ b/src/device.c
@@ -120,6 +120,7 @@ static netdev_tx_t xmit(struct sk_buff *skb, struct net_device *dev)
struct sk_buff *next;
struct sk_buff_head packets;
sa_family_t family;
+ u32 mtu;
int ret;
if (unlikely(skb_examine_untrusted_ip_hdr(skb) != skb->protocol)) {
@@ -142,6 +143,8 @@ static netdev_tx_t xmit(struct sk_buff *skb, struct net_device *dev)
goto err_peer;
}
+ mtu = dst_mtu(skb_dst(skb)) ?: skb->dev->mtu;
+
__skb_queue_head_init(&packets);
if (!skb_is_gso(skb))
skb->next = NULL;
@@ -168,6 +171,8 @@ static netdev_tx_t xmit(struct sk_buff *skb, struct net_device *dev)
*/
skb_dst_drop(skb);
+ PACKET_CB(skb)->mtu = mtu;
+
__skb_queue_tail(&packets, skb);
} while ((skb = next) != NULL);
diff --git a/src/queueing.h b/src/queueing.h
index d5948f3..c507536 100644
--- a/src/queueing.h
+++ b/src/queueing.h
@@ -46,6 +46,7 @@ struct packet_cb {
u64 nonce;
struct noise_keypair *keypair;
atomic_t state;
+ u32 mtu;
u8 ds;
};
#define PACKET_PEER(skb) (((struct packet_cb *)skb->cb)->keypair->entry.peer)
diff --git a/src/send.c b/src/send.c
index dddcc0b..e3b1ffd 100644
--- a/src/send.c
+++ b/src/send.c
@@ -116,11 +116,11 @@ static inline unsigned int skb_padding(struct sk_buff *skb)
* isn't strictly neccessary, but it's better to be cautious here, especially
* if that code ever changes.
*/
- unsigned int last_unit = skb->len % skb->dev->mtu;
+ unsigned int last_unit = skb->len % PACKET_CB(skb)->mtu;
unsigned int padded_size = (last_unit + MESSAGE_PADDING_MULTIPLE - 1) & ~(MESSAGE_PADDING_MULTIPLE - 1);
- if (padded_size > skb->dev->mtu)
- padded_size = skb->dev->mtu;
+ if (padded_size > PACKET_CB(skb)->mtu)
+ padded_size = PACKET_CB(skb)->mtu;
return padded_size - last_unit;
}
next prev parent reply other threads:[~2018-04-14 2:26 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-16 9:25 Roman Mamedov
2018-03-16 9:35 ` Matthias Ordner
2018-03-16 10:53 ` Roman Mamedov
2018-03-16 16:20 ` Roman Mamedov
2018-03-16 10:01 ` Kalin KOZHUHAROV
2018-03-26 19:12 ` Luis Ressel
2018-04-14 1:38 ` Jason A. Donenfeld
2018-04-14 2:40 ` Jason A. Donenfeld [this message]
2018-04-14 13:16 ` Jason A. Donenfeld
2018-04-14 13:40 ` Roman Mamedov
2018-04-14 14:15 ` Jason A. Donenfeld
2018-04-14 14:38 ` Roman Mamedov
2018-04-14 14:45 ` Jason A. Donenfeld
2018-04-14 15:20 ` Roman Mamedov
2018-04-14 23:08 ` Jason A. Donenfeld
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