netdev - Re: [PATCH 1/1] net: usb: qmi_wwan: restore mtu min/max values after raw

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Date:   Sun, 23 Feb 2020 14:40:51 +0100
From:   Bjørn Mork <bjorn@...k.no>
To:     Daniele Palmas <dnlplm@...il.com>
Cc:     netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH 1/1] net: usb: qmi_wwan: restore mtu min/max values after raw_ip switch

Daniele Palmas <dnlplm@...il.com> writes:

> usbnet creates network interfaces with min_mtu = 0 and
> max_mtu = ETH_MAX_MTU.
>
> These values are not modified by qmi_wwan when the network interface
> is created initially, allowing, for example, to set mtu greater than 1500.
>
> When a raw_ip switch is done (raw_ip set to 'Y', then set to 'N') the mtu
> values for the network interface are set through ether_setup, with
> min_mtu = ETH_MIN_MTU and max_mtu = ETH_DATA_LEN, not allowing anymore to
> set mtu greater than 1500 (error: mtu greater than device maximum).
>
> The patch restores the original min/max mtu values set by usbnet after a
> raw_ip switch.
>
> Signed-off-by: Daniele Palmas <dnlplm@...il.com>

Great! I tried to look up the origin of this bug, and it seems to be a
hard-to-spot fallout from the 'centralized MTU checking'.  Not easy to
see the hidden connection in usbnet.c and eth.c. Thanks for finding and
fixing it!

This should probably go to stable as well?

Acked-by: Bjørn Mork <bjorn@...k.no>