On Wed, 13 Dec 2017 23:37:00 +0100
Stefano Brivio <[email protected]> wrote:
> Commit a985343ba906 ("vxlan: refactor verification and
> application of configuration") introduced a change in the
> behaviour of initial MTU setting: earlier, the MTU for a link
> created on top of a given lower device, without an initial MTU
> specification, was set to the MTU of the lower device minus
> headroom as a result of this path in vxlan_dev_configure():
>
> if (!conf->mtu)
> dev->mtu = lowerdev->mtu -
> (use_ipv6 ? VXLAN6_HEADROOM : VXLAN_HEADROOM);
>
> which is now gone. Now, the initial MTU, in absence of a
> configured value, is simply set by ether_setup() to ETH_DATA_LEN
> (1500 bytes).
>
> This breaks userspace expectations in case the MTU of
> the lower device is higher than 1500 bytes minus headroom.
>
> Restore the previous behaviour by calculating, for a new link,
> the MTU from the lower device, if present, and if no value is
> explicitly configured.
>
> Reported-by: Junhan Yan <[email protected]>
> Fixes: a985343ba906 ("vxlan: refactor verification and application of
> configuration")
> Signed-off-by: Stefano Brivio <[email protected]>
> ---
Good catch.
Acked-by: Stephen Hemminger <[email protected]>
