This is a note to let you know that I've just added the patch titled macvlan: enforce a consistent minimal mtu to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: macvlan-enforce-a-consistent-minimal-mtu.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From b64085b00044bdf3cd1c9825e9ef5b2e0feae91a Mon Sep 17 00:00:00 2001 From: Eric Dumazet <edumazet@xxxxxxxxxx> Date: Fri, 7 Oct 2022 15:57:43 -0700 Subject: macvlan: enforce a consistent minimal mtu From: Eric Dumazet <edumazet@xxxxxxxxxx> commit b64085b00044bdf3cd1c9825e9ef5b2e0feae91a 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: 91572088e3fd ("net: use core MTU range checking in core net infra") Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/net/macvlan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/drivers/net/macvlan.c +++ b/drivers/net/macvlan.c @@ -1166,7 +1166,7 @@ void macvlan_common_setup(struct net_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); Patches currently in stable-queue which might be from edumazet@xxxxxxxxxx are queue-5.4/net-tun-fix-memory-leaks-of-napi_get_frags.patch queue-5.4/kcm-avoid-potential-race-in-kcm_tx_work.patch queue-5.4/macvlan-enforce-a-consistent-minimal-mtu.patch queue-5.4/bpf-test_run-fix-alignment-problem-in-bpf_prog_test_run_skb.patch queue-5.4/tcp-cdg-allow-tcp_cdg_release-to-be-called-multiple-times.patch queue-5.4/net-tun-call-napi_schedule_prep-to-ensure-we-own-a-napi.patch