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

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Date: Fri, 26 May 2023 20:00:08 +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

I will rework the patch.

Best regards,

Vlad.

On 26.05.2023 19:47, Eric Dumazet wrote:
> On Fri, May 26, 2023 at 6:41 PM Vlad Efanov <vefanov@...ras.ru> wrote:
>> 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);
>> }
> I am quite familiar with this code.
>
> What are you trying to say exactly ?
>
> Please come with a V2 without grabbing the socket lock.