netdev - Re: [PATCH net-next] ipv4/fib: send RTM

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Date: Tue, 18 Jul 2023 13:19:06 +0300
From: Ido Schimmel <idosch@...sch.org>
To: Hangbin Liu <liuhangbin@...il.com>
Cc: netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
	David Ahern <dsahern@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Thomas Haller <thaller@...hat.com>
Subject: Re: [PATCH net-next] ipv4/fib: send RTM_DELROUTE notify when flush
 fib

On Tue, Jul 18, 2023 at 04:00:44PM +0800, Hangbin Liu wrote:
> After deleting an interface address in fib_del_ifaddr(), the function
> scans the fib_info list for stray entries and calls fib_flush.
> Then the stray entries will be deleted silently and no RTM_DELROUTE
> notification will be sent.

[...]

> diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
> index 74d403dbd2b4..1a88013f6a5b 100644
> --- a/net/ipv4/fib_trie.c
> +++ b/net/ipv4/fib_trie.c
> @@ -2026,6 +2026,7 @@ void fib_table_flush_external(struct fib_table *tb)
>  int fib_table_flush(struct net *net, struct fib_table *tb, bool flush_all)
>  {
>  	struct trie *t = (struct trie *)tb->tb_data;
> +	struct nl_info info = { .nl_net = net };
>  	struct key_vector *pn = t->kv;
>  	unsigned long cindex = 1;
>  	struct hlist_node *tmp;
> @@ -2088,6 +2089,8 @@ int fib_table_flush(struct net *net, struct fib_table *tb, bool flush_all)
>  
>  			fib_notify_alias_delete(net, n->key, &n->leaf, fa,
>  						NULL);
> +			rtmsg_fib(RTM_DELROUTE, htonl(n->key), fa,
> +				  KEYLENGTH - fa->fa_slen, tb->tb_id, &info, 0);

fib_table_flush() isn't only called when an address is deleted, but also
when an interface is deleted or put down. The lack of notification in
these cases is deliberate. Commit 7c6bb7d2faaf ("net/ipv6: Add knob to
skip DELROUTE message on device down") introduced a sysctl to make IPv6
behave like IPv4 in this regard, but this patch breaks it.

IMO, the number of routes being flushed because a preferred source
address is deleted is significantly lower compared to interface down /
deletion, so generating notifications in this case is probably OK. It
also seems to be consistent with IPv6 given that rt6_remove_prefsrc()
calls fib6_clean_all() and not fib6_clean_all_skip_notify().

>  			hlist_del_rcu(&fa->fa_list);
>  			fib_release_info(fa->fa_info);
>  			alias_free_mem_rcu(fa);
> -- 
> 2.38.1
> 
>