netdev - Re: [PATCH v1 net-next 6/6] fib: rules: Convert RTM

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Message-ID: <CANn89iLhtzeM+0oO_SQuK5sbj_ueVk63wE37qhS84wPdc-jbzw@mail.gmail.com>
Date: Thu, 6 Feb 2025 10:41:12 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v1 net-next 6/6] fib: rules: Convert RTM_DELRULE to
 per-netns RTNL.

On Thu, Feb 6, 2025 at 9:49 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
>
> fib_nl_delrule() is the doit() handler for RTM_DELRULE but also called
> 1;95;0cfrom vrf_newlink() in case something fails in vrf_add_fib_rules().
>
> In the latter case, RTNL is already held and the 3rd arg extack is NULL.
>
> Let's hold per-netns RTNL in fib_nl_delrule() if extack is NULL.
>
> Now we can place ASSERT_RTNL_NET() in call_fib_rule_notifiers().
>
> While at it, fib_rule r is moved to the suitable scope.
>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> ---
>  net/core/fib_rules.c | 29 +++++++++++++++++++----------
>  1 file changed, 19 insertions(+), 10 deletions(-)
>
> diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
> index cc26c762fa9e..3430d026134d 100644
> --- a/net/core/fib_rules.c
> +++ b/net/core/fib_rules.c
> @@ -371,7 +371,8 @@ static int call_fib_rule_notifiers(struct net *net,
>                 .rule = rule,
>         };
>
> -       ASSERT_RTNL();
> +       ASSERT_RTNL_NET(net);

This warning will then fire in the vrf case, because vrf_fib_rule() is
only holding the real RTNL,
but not yet the net->rtnl_mutex ?

> +
>         /* Paired with READ_ONCE() in fib_rules_seq() */
>         WRITE_ONCE(ops->fib_rules_seq, ops->fib_rules_seq + 1);
>         return call_fib_notifiers(net, event_type, &info.info);
> @@ -909,13 +910,13 @@ EXPORT_SYMBOL_GPL(fib_nl_newrule);
>  int fib_nl_delrule(struct sk_buff *skb, struct nlmsghdr *nlh,
>                    struct netlink_ext_ack *extack)
>  {
> -       struct net *net = sock_net(skb->sk);
> +       bool user_priority = false, hold_rtnl = !!extack;

I am not pleased with this heuristic hidden here.

At the very least a fat comment in drivers/net/vrf.c would be welcomed.


> +       struct fib_rule *rule = NULL, *nlrule = NULL;
>         struct fib_rule_hdr *frh = nlmsg_data(nlh);
> +       struct net *net = sock_net(skb->sk);
>         struct fib_rules_ops *ops = NULL;
> -       struct fib_rule *rule = NULL, *r, *nlrule = NULL;
>         struct nlattr *tb[FRA_MAX+1];
>         int err = -EINVAL;
> -       bool user_priority = false;
>
>         if (nlh->nlmsg_len < nlmsg_msg_size(sizeof(*frh))) {
>                 NL_SET_ERR_MSG(extack, "Invalid msg length");
> @@ -940,6 +941,9 @@ int fib_nl_delrule(struct sk_buff *skb, struct nlmsghdr *nlh,
>         if (err)
>                 goto errout;
>
> +       if (hold_rtnl)
> +               rtnl_net_lock(net);
> +
>         err = fib_nl2rule_rtnl(nlrule, ops, tb, extack);
>         if (err)
>                 goto errout_free;
> @@ -980,7 +984,7 @@ int fib_nl_delrule(struct sk_buff *skb, struct nlmsghdr *nlh,
>          * current if it is goto rule, have actually been added.
>          */
>         if (ops->nr_goto_rules > 0) {
> -               struct fib_rule *n;
> +               struct fib_rule *n, *r;
>
>                 n = list_next_entry(rule, list);
>                 if (&n->list == &ops->rules_list || n->pref != rule->pref)
> @@ -994,10 +998,12 @@ int fib_nl_delrule(struct sk_buff *skb, struct nlmsghdr *nlh,
>                 }
>         }
>
> -       call_fib_rule_notifiers(net, FIB_EVENT_RULE_DEL, rule, ops,
> -                               NULL);
> -       notify_rule_change(RTM_DELRULE, rule, ops, nlh,
> -                          NETLINK_CB(skb).portid);
> +       call_fib_rule_notifiers(net, FIB_EVENT_RULE_DEL, rule, ops, NULL);
> +
> +       if (hold_rtnl)
> +               rtnl_net_unlock(net);
> +
> +       notify_rule_change(RTM_DELRULE, rule, ops, nlh, NETLINK_CB(skb).portid);
>         fib_rule_put(rule);
>         flush_route_cache(ops);
>         rules_ops_put(ops);
> @@ -1005,6 +1011,8 @@ int fib_nl_delrule(struct sk_buff *skb, struct nlmsghdr *nlh,
>         return 0;
>
>  errout_free:
> +       if (hold_rtnl)
> +               rtnl_net_unlock(net);
>         kfree(nlrule);
>  errout:
>         rules_ops_put(ops);
> @@ -1324,7 +1332,8 @@ static struct pernet_operations fib_rules_net_ops = {
>  static const struct rtnl_msg_handler fib_rules_rtnl_msg_handlers[] __initconst = {
>         {.msgtype = RTM_NEWRULE, .doit = fib_nl_newrule,
>          .flags = RTNL_FLAG_DOIT_PERNET},
> -       {.msgtype = RTM_DELRULE, .doit = fib_nl_delrule},
> +       {.msgtype = RTM_DELRULE, .doit = fib_nl_delrule,
> +        .flags = RTNL_FLAG_DOIT_PERNET},
>         {.msgtype = RTM_GETRULE, .dumpit = fib_nl_dumprule,
>          .flags = RTNL_FLAG_DUMP_UNLOCKED},
>  };
> --
> 2.39.5 (Apple Git-154)
>