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Message-ID: <jsfa7qvqpspyau47xrqz5gxpzdxfyeyszbhcyuwx7ermzjahaf@jrznbsy3f722>
Date: Thu, 3 Jul 2025 13:04:24 +0200
From: Gabriel Goller <g.goller@...xmox.com>
To: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
Jonathan Corbet <corbet@....net>, David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] ipv6: add `force_forwarding` sysctl to enable
per-interface forwarding
On 02.07.2025 12:05, Nicolas Dichtel wrote:
>Le 02/07/2025 à 09:46, Gabriel Goller a écrit :
>> It is currently impossible to enable ipv6 forwarding on a per-interface
>> basis like in ipv4. To enable forwarding on an ipv6 interface we need to
>> enable it on all interfaces and disable it on the other interfaces using
>> a netfilter rule. This is especially cumbersome if you have lots of
>> interface and only want to enable forwarding on a few. According to the
>> sysctl docs [0] the `net.ipv6.conf.all.forwarding` enables forwarding
>> for all interfaces, while the interface-specific
>> `net.ipv6.conf.<interface>.forwarding` configures the interface
>> Host/Router configuration.
>>
>> Introduce a new sysctl flag `force_forwarding`, which can be set on every
>> interface. The ip6_forwarding function will then check if the global
>> forwarding flag OR the force_forwarding flag is active and forward the
>> packet.
>>
>> To preserver backwards-compatibility reset the flag (on all interfaces)
>> to 0 if the net.ipv6.conf.all.forwarding flag is set to 0.
>>
>> [0]: https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt
>>
>> Signed-off-by: Gabriel Goller <g.goller@...xmox.com>
>> ---
>>
>Please, wait 24 hours before reposting.
>https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/maintainer-netdev.rst#n419
Ah, my bad, thought I posted v2 in the morning as well :(
>[snip]
>
>> @@ -6747,6 +6759,77 @@ static int addrconf_sysctl_disable_policy(const struct ctl_table *ctl, int write
>> return ret;
>> }
>>
>> +/* called with RTNL locked */
>Instead of a comment ...
>
>> +static void addrconf_force_forward_change(struct net *net, __s32 newf)
>> +{
>> + struct net_device *dev;
>> + struct inet6_dev *idev;
>> +
>... put
>
> ASSERT_RTNL();
>
Agree.
>> + for_each_netdev(net, dev) {
>> + idev = __in6_dev_get_rtnl_net(dev);
>> + if (idev) {
>> + int changed = (!idev->cnf.force_forwarding) ^ (!newf);
>> +
>> + WRITE_ONCE(idev->cnf.force_forwarding, newf);
>> + if (changed) {
>> + inet6_netconf_notify_devconf(dev_net(dev), RTM_NEWNETCONF,
>> + NETCONFA_FORCE_FORWARDING,
>> + dev->ifindex, &idev->cnf);
>> + }
>> + }
>> + }
>> +}
>> +
>> +static int addrconf_sysctl_force_forwarding(const struct ctl_table *ctl, int write,
>> + void *buffer, size_t *lenp, loff_t *ppos)
>> +{
>> + int *valp = ctl->data;
>> + int ret;
>> + int old, new;
>> +
>> + // get extra params from table
>/* */ for comment
>https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/coding-style.rst#n598
NAK
(https://lore.kernel.org/lkml/CA+55aFyQYJerovMsSoSKS7PessZBr4vNp-3QUUwhqk4A4_jcbg@mail.gmail.com/#r)
But I'll capitalize the first word.
>> + struct inet6_dev *idev = ctl->extra1;
>> + struct net *net = ctl->extra2;
>Reverse x-mas tree for the variables declaration
>https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/maintainer-netdev.rst#n368
Done.
>> +
>> + // copy table and change extra params to min/max so we can use proc_douintvec_minmax
>> + struct ctl_table lctl;
>> +
>> + lctl = *ctl;
>> + lctl.extra1 = SYSCTL_ZERO;
>> + lctl.extra2 = SYSCTL_ONE;
>> +
>> + old = *valp;
>> + ret = proc_douintvec_minmax(&lctl, write, buffer, lenp, ppos);
>> + new = *valp;
>I probably missed something. The new value is written in lctl. When is it
>written in ctl?
Ah, sorry there is something missing here.
This is supposed to look like this:
struct inet6_dev *idev = ctl->extra1;
struct net *net = ctl->extra2;
int *valp = ctl->data;
loff_t pos = *ppos;
int new = *valp;
int old = *valp;
int ret;
struct ctl_table lctl;
lctl = *ctl;
lctl.extra1 = SYSCTL_ZERO;
lctl.extra2 = SYSCTL_ONE;
lctl.data = &new;
ret = proc_douintvec_minmax(&lctl, write, buffer, lenp, ppos);
...
if (write)
WRITE_ONCE(*valp, new);
if (ret)
*ppos = pos;
return ret;
>> +
>> + if (write && old != new) {
>> + if (!rtnl_net_trylock(net))
>> + return restart_syscall();
>> +
>> + if (valp == &net->ipv6.devconf_dflt->force_forwarding) {
>> + inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
>> + NETCONFA_FORCE_FORWARDING,
>> + NETCONFA_IFINDEX_DEFAULT,
>> + net->ipv6.devconf_dflt);
>> + } else if (valp == &net->ipv6.devconf_all->force_forwarding) {
>> + inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
>> + NETCONFA_FORCE_FORWARDING,
>> + NETCONFA_IFINDEX_ALL,
>> + net->ipv6.devconf_all);
>> +
>> + addrconf_force_forward_change(net, new);
>> + } else {
>> + inet6_netconf_notify_devconf(net, RTM_NEWNETCONF,
>> + NETCONFA_FORCE_FORWARDING,
>> + idev->dev->ifindex,
>> + &idev->cnf);
>> + }
>> + rtnl_net_unlock(net);
>> + }
>> +
>> + return ret;
>> +}
>> +
>> static int minus_one = -1;
>> static const int two_five_five = 255;
>> static u32 ioam6_if_id_max = U16_MAX;
Thanks for the review!
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