macvlan: enforce a consistent minimal mtu

stable inclusion
from stable-v5.10.156
commit e929ec98c0c3b10d9c07f3776df0c1a02d7a763e
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I67UR2
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e929ec98c0c3b10d9c07f3776df0c1a02d7a763e

--------------------------------

commit b64085b0 upstream.

macvlan should enforce a minimal mtu of 68, even at link creation.

This patch avoids the current behavior (which could lead to crashes
in ipv6 stack if the link is brought up)

$ ip link add macvlan1 link eno1 mtu 8 type macvlan  # This should fail !
$ ip link sh dev macvlan1
5: macvlan1@eno1: <BROADCAST,MULTICAST> mtu 8 qdisc noop
    state DOWN mode DEFAULT group default qlen 1000
    link/ether 02:47:6c:24:74:82 brd ff:ff:ff:ff:ff:ff
$ ip link set macvlan1 mtu 67
Error: mtu less than device minimum.
$ ip link set macvlan1 mtu 68
$ ip link set macvlan1 mtu 8
Error: mtu less than device minimum.

Fixes: 91572088 ("net: use core MTU range checking in core net infra")
Reported-by: Nsyzbot <syzkaller@googlegroups.com>
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NZhengchao Shao <shaozhengchao@huawei.com>
Reviewed-by: NLiu Jian <liujian56@huawei.com>
Signed-off-by: NJialin Zhang <zhangjialin11@huawei.com>

drivers/net/macvlan.c

@@ -1176,7 +1176,7 @@ void macvlan_common_setup(struct net_device *dev)
 {
 	ether_setup(dev);
 
-	dev->min_mtu		= 0;
+	/* ether_setup() has set dev->min_mtu to ETH_MIN_MTU. */
 	dev->max_mtu		= ETH_MAX_MTU;
 	dev->priv_flags	       &= ~IFF_TX_SKB_SHARING;
 	netif_keep_dst(dev);