linux-kernel - [PATCH 5.10 018/146] vrf: fix maximum MTU

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Date:   Mon, 21 Jun 2021 18:14:08 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Miaohe Lin <linmiaohe@...wei.com>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        David Ahern <dsahern@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.10 018/146] vrf: fix maximum MTU

From: Nicolas Dichtel <nicolas.dichtel@...nd.com>

[ Upstream commit 9bb392f62447d73cc7dd7562413a2cd9104c82f8 ]

My initial goal was to fix the default MTU, which is set to 65536, ie above
the maximum defined in the driver: 65535 (ETH_MAX_MTU).

In fact, it's seems more consistent, wrt min_mtu, to set the max_mtu to
IP6_MAX_MTU (65535 + sizeof(struct ipv6hdr)) and use it by default.

Let's also, for consistency, set the mtu in vrf_setup(). This function
calls ether_setup(), which set the mtu to 1500. Thus, the whole mtu config
is done in the same function.

Before the patch:
$ ip link add blue type vrf table 1234
$ ip link list blue
9: blue: <NOARP,MASTER> mtu 65536 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether fa:f5:27:70:24:2a brd ff:ff:ff:ff:ff:ff
$ ip link set dev blue mtu 65535
$ ip link set dev blue mtu 65536
Error: mtu greater than device maximum.

Fixes: 5055376a3b44 ("net: vrf: Fix ping failed when vrf mtu is set to 0")
CC: Miaohe Lin <linmiaohe@...wei.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Reviewed-by: David Ahern <dsahern@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/net/vrf.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c
index b9b7e00b72a8..bc96ac0c5769 100644
--- a/drivers/net/vrf.c
+++ b/drivers/net/vrf.c
@@ -1184,9 +1184,6 @@ static int vrf_dev_init(struct net_device *dev)
 
 	dev->flags = IFF_MASTER | IFF_NOARP;
 
-	/* MTU is irrelevant for VRF device; set to 64k similar to lo */
-	dev->mtu = 64 * 1024;
-
 	/* similarly, oper state is irrelevant; set to up to avoid confusion */
 	dev->operstate = IF_OPER_UP;
 	netdev_lockdep_set_classes(dev);
@@ -1620,7 +1617,8 @@ static void vrf_setup(struct net_device *dev)
 	 * which breaks networking.
 	 */
 	dev->min_mtu = IPV6_MIN_MTU;
-	dev->max_mtu = ETH_MAX_MTU;
+	dev->max_mtu = IP6_MAX_MTU;
+	dev->mtu = dev->max_mtu;
 }
 
 static int vrf_validate(struct nlattr *tb[], struct nlattr *data[],
-- 
2.30.2