[PATCH net] macvlan: enforce a consistent minimal mtu

[PATCH net] macvlan: enforce a consistent minimal mtu

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

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: 91572088e3fd ("net: use core MTU range checking in core net infra")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 drivers/net/macvlan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index 713e3354cb2eb14cbf4009e67858c261508a037b..8f8f73099de8d8308b45b7e3bf9179e8311182ee 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -1192,7 +1192,7 @@ 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);
-- 
2.38.0.rc1.362.ged0d419d3c-goog

Re: [PATCH net] macvlan: enforce a consistent minimal mtu

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (master)
by David S. Miller <davem@davemloft.net>:

On Fri,  7 Oct 2022 15:57:43 -0700 you wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> 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)
> 
> [...]

Here is the summary with links:
  - [net] macvlan: enforce a consistent minimal mtu
    https://git.kernel.org/netdev/net/c/b64085b00044

You are awesome, thank you!
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