netdev - Re: [PATCH v2 net-next 08/19] ipmr: do not acquire mrt_lock while calling ip_mr

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Message-ID: <20220722211530.ywhc6pao4s6rx2ad@skbuf>
Date:   Sat, 23 Jul 2022 00:15:30 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH v2 net-next 08/19] ipmr: do not acquire mrt_lock while
 calling ip_mr_forward()

On Sat, Jul 23, 2022 at 12:10:05AM +0300, Vladimir Oltean wrote:
> I just noticed that we appear to have the same problem with the
> equivalent call path for ipv6: ip6mr_mfc_add -> ip6mr_cache_resolve ->
> ip6_mr_forward, although I don't have smcroute or the kernel configured
> for any IPv6 multicast routes right now, so I can't say for sure.

Not to mention ip6_mr_forward() has a random rcu_read_unlock() thrown in
there, with no paired lock(), left from who knows what refactoring...
I don't think I'll be able to report all the locking problems with the
IP multicast routing code, maybe someone with more familiarity should
take a look there :-/