netdev - Re: Stack sends oversize UDP packet to the driver

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Date:   Mon, 21 Jan 2019 16:59:15 -0800
From:   Michael Chan <michael.chan@...adcom.com>
To:     Daniel Axtens <dja@...ens.net>
Cc:     Netdev <netdev@...r.kernel.org>, David Miller <davem@...emloft.net>
Subject: Re: Stack sends oversize UDP packet to the driver

On Mon, Jan 21, 2019 at 4:36 PM Daniel Axtens <dja@...ens.net> wrote:

> I hit a similar sounding issue on a bnx2x - see commit
> 8914a595110a6eca69a5e275b323f5d09e18f4f9
>
> In that case, a GSO packet with gso_size too large for the firmware was
> coming to the bnx2x driver from an ibmveth device via Open vSwitch. I
> also toyed with a fix in the stack and ended up fixing just the driver.

Hi Daniel, yes I remember the issue that you reported at that time.
The current issue is similar but for non-TSO UDP packets.

>
> I was hoping to get a generic fix in to the stack afterwards, but didn't
> get anything finished. Looking back at old branches, it looks like I
> considered adding MTU validation to validate_xmit_skb,

MTU validation in validate_xmit_skb() would definitely prevent the
current reported issue.  Perhaps we can add a WARN() when an invalid
length is detected so that the underlying issue will be reported and
fixed.  The current issue is that somehow the dst of the SKB gets
changed to "lo" and fragmentation is not done for the proper output
device.  Thanks.