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Message-ID: <Zy3/TmyK7imjT348@debian>
Date: Fri, 8 Nov 2024 13:08:46 +0100
From: Guillaume Nault <gnault@...hat.com>
To: Emanuele Santini <emanuele.santini.88@...il.com>
Cc: netdev@...r.kernel.org, yoshfuji@...ux-ipv6.org, friedrich@...age.de,
kuba@...nel.org, davem@...emloft.net, pabeni@...hat.com,
dsahern@...nel.org
Subject: Re: [PATCH] net: ipv6: fix the address length for net_device on a
GRE tunnel
On Fri, Nov 08, 2024 at 10:25:55AM +0100, Emanuele Santini wrote:
> While GRE tunneling does not require
> a hardware address, a random Ethernet address is still assigned to
> the 'net_device'.
That's really surprising and not what I can see on my system. Are you
really talking about ip6gre (and not ip6gretap)?
> Therefore, the correct 'addr_len' value should be
> the size of an Ethernet address (6 bytes), not the size of an IPv6
> address.
Ethernet address length only makes sense for ip6gretap. This doesn't
seem like a valid justification for ip6gre.
> This fix sets 'addr_len' to the appropriate value, ensuring
> consistency in the net_device setup for IPv6 GRE tunnels.
>
> Bug: Setting addr_len to the size of an IPv6 network address (16 bytes)
> can cause a packet socket with SOCK_DGRAM to fail on 'sendto' calls.
> This happens due to a check in 'packet_snd' for SOCK_DGRAM types,
> which validates the address length.
>
> This bug was introduced in kernel version 4.20.0 and is still present in the current version.
>
> Steps to reproduce:
>
> ip -6 tunnel add <dev_name> mode ip6gre remote <remote_addr> local <local_addr> ttl 255
> ip link set dev <dev_name> up
> busybox udhcpc -i <dev_name> -n -f
> -> It returns Invalid Argument.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=202147
> Reported-by: Friedrich Oslage <friedrich@...age.de>
> Signed-off-by: Emanuele Santini <emanuele.santini.88@...il.com>
> ---
> net/ipv6/ip6_gre.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
> index 235808cfec70..db7679b04a02 100644
> --- a/net/ipv6/ip6_gre.c
> +++ b/net/ipv6/ip6_gre.c
> @@ -1455,7 +1455,7 @@ static void ip6gre_tunnel_setup(struct net_device *dev)
> dev->type = ARPHRD_IP6GRE;
>
> dev->flags |= IFF_NOARP;
> - dev->addr_len = sizeof(struct in6_addr);
> + dev->addr_len = ETH_ALEN;
I guess it should be "dev->addr_len = 0" instead. We have no "hardware"
address.
> netif_keep_dst(dev);
> /* This perm addr will be used as interface identifier by IPv6 */
> dev->addr_assign_type = NET_ADDR_RANDOM;
> --
> 2.46.0
>
>
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