netdev - Re: [PATCH v4 net] rxrpc: fix race condition in rxrpc_input

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Message-Id: <20190424.141256.91264571846390685.davem@davemloft.net>
Date:   Wed, 24 Apr 2019 14:12:56 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        syzkaller@...glegroups.com, dhowells@...hat.com
Subject: Re: [PATCH v4 net] rxrpc: fix race condition in
 rxrpc_input_packet()

From: Eric Dumazet <edumazet@...gle.com>
Date: Wed, 24 Apr 2019 09:44:11 -0700

> After commit 5271953cad31 ("rxrpc: Use the UDP encap_rcv hook"),
> rxrpc_input_packet() is directly called from lockless UDP receive
> path, under rcu_read_lock() protection.
> 
> It must therefore use RCU rules :
> 
> - udp_sk->sk_user_data can be cleared at any point in this function.
>   rcu_dereference_sk_user_data() is what we need here.
> 
> - Also, since sk_user_data might have been set in rxrpc_open_socket()
>   we must observe a proper RCU grace period before kfree(local) in
>   rxrpc_lookup_local()
> 
> v4: @local can be NULL in xrpc_lookup_local() as reported by kbuild test robot <lkp@...el.com>
>         and Julia Lawall <julia.lawall@...6.fr>, thanks !
> 
> v3,v2 : addressed David Howells feedback, thanks !
> 
> syzbot reported :
 ...
> Fixes: 5271953cad31 ("rxrpc: Use the UDP encap_rcv hook")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Acked-by: David Howells <dhowells@...hat.com>

Applied and queued up for v4.19+ -stable.

Thanks.