Re: [PATCH] udp6: Fix race condition in udp6_sendmsg & connect

Vlad Efanov
2023-05-26T16:41:14Z

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@ispras.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.