netdev - Re: [PATCH] udp6: Fix race condition in udp6

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Message-ID: <d3fccbd0-c92e-9aff-8c32-48c1171746c3@ispras.ru>
Date: Fri, 26 May 2023 19:41:07 +0300
From: Vlad Efanov <vefanov@...ras.ru>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Paolo Abeni <pabeni@...hat.com>,
 Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>,
 Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org
Subject: Re: [PATCH] udp6: Fix race condition in udp6_sendmsg & connect

sk_dst_set() is called by sk_setup_caps().

sk_dst_set() replaces dst in socket using xchg() call and we still have 
two tasks use one socket but expect different dst in sk_dst_cache.

__sk_dst_set() is rcu protected, but it checks for socket lock.

static inline void
__sk_dst_set(struct sock *sk, struct dst_entry *dst)
{
     struct dst_entry *old_dst;

     sk_tx_queue_clear(sk);
     sk->sk_dst_pending_confirm = 0;
     old_dst = rcu_dereference_protected(sk->sk_dst_cache,
                         lockdep_sock_is_held(sk));
     rcu_assign_pointer(sk->sk_dst_cache, dst);
     dst_release(old_dst);
}

Best regards.

Vlad.

On 26.05.2023 19:00, Eric Dumazet wrote:
> On Fri, May 26, 2023 at 5:58 PM Ефанов Владислав Александрович
> <vefanov@...ras.ru> wrote:
>> Paolo,
>>
>>
>> I don't think that we can just move sk_dst_set() call.
>>
>> I think we can destroy dst of sendmsg task in this case.
>>
> dst are RCU protected, it should be easy to make sure we respect all the rules.