netdev - Re: [PATCH net 1/2] net: nexthop: dereference nh only once in nexthop_select

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Message-ID: <54c02cfa-00be-1379-1965-5ab833d3d5b1@gmail.com>
Date:   Tue, 19 May 2020 09:51:34 -0600
From:   David Ahern <dsahern@...il.com>
To:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        netdev@...r.kernel.org
Cc:     roopa@...ulusnetworks.com
Subject: Re: [PATCH net 1/2] net: nexthop: dereference nh only once in
 nexthop_select_path

On 5/19/20 5:04 AM, Nikolay Aleksandrov wrote:
> the ->nh pointer might become suddenly null while we're selecting the
> path and we may dereference it. Dereference it only once in the
> beginning and use that if it's not null, we rely on the refcounting and
> rcu to protect against use-after-free.

the num_nh is also affected. I think an rcu update of the entire nh_grp
is the better solution. Dataplane should always see a valid nh_grp via rcu.