From: Alexey Kodanev <alexey.koda...@oracle.com>
Date: Thu, 14 Dec 2017 20:20:00 +0300
> Stefano Brivio says:
> 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.
>
> This patch restores the previous behaviour on newlink operation. Since
> max_mtu can be negative and we update dev->mtu directly, also check it
> for valid minimum.
>
> Reported-by: Junhan Yan <ju...@redhat.com>
> Fixes: a985343ba906 ("vxlan: refactor verification and application of
> configuration")
> Signed-off-by: Alexey Kodanev <alexey.koda...@oracle.com>
Applied and queued up for -stable, thanks.
