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

[Vlad Efanov]

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@xxxxxxxxx> 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.