netdev - Re: [PATCH net v6 09/10] ip6mr: Lock RCU before ip6mr_get_table() call in ip6mr_rtm

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Message-ID: <20241017181446.GC25857@breakpoint.cc>
Date: Thu, 17 Oct 2024 20:14:46 +0200
From: Florian Westphal <fw@...len.de>
To: Stefan Wiehler <stefan.wiehler@...ia.com>
Cc: "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>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v6 09/10] ip6mr: Lock RCU before ip6mr_get_table()
 call in ip6mr_rtm_getroute()

Stefan Wiehler <stefan.wiehler@...ia.com> wrote:
> When IPV6_MROUTE_MULTIPLE_TABLES is enabled, multicast routing tables
> must be read under RCU or RTNL lock.
> 
> Fixes: d1db275dd3f6 ("ipv6: ip6mr: support multiple tables")
> Signed-off-by: Stefan Wiehler <stefan.wiehler@...ia.com>
> ---
>  net/ipv6/ip6mr.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
> index b169b27de7e1..39aac81a30f1 100644
> --- a/net/ipv6/ip6mr.c
> +++ b/net/ipv6/ip6mr.c
> @@ -2633,27 +2633,31 @@ static int ip6mr_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
>  		grp = nla_get_in6_addr(tb[RTA_DST]);
>  	tableid = tb[RTA_TABLE] ? nla_get_u32(tb[RTA_TABLE]) : 0;
>  
> +	rcu_read_lock();

AFAICS ip6mr_rtm_getroute() runs with RTNL held, so I don't see
why this patch is needed.