John Fastabend wrote:
> Eric Dumazet wrote:
> > On Tue, May 23, 2023 at 4:56 AM John Fastabend <john.fastabend@xxxxxxxxx> wrote:
> > >
> > > When TCP stack has data ready to read sk_data_ready() is called. Sockmap
> > > overwrites this with its own handler to call into BPF verdict program.
> > > But, the original TCP socket had sock_def_readable that would additionally
> > > wake up any user space waiters with sk_wake_async().
> > >
> > > Sockmap saved the callback when the socket was created so call the saved
> > > data ready callback and then we can wake up any epoll() logic waiting
> > > on the read.
> > >
> > > Note we call on 'copied >= 0' to account for returning 0 when a FIN is
> > > received because we need to wake up user for this as well so they
> > > can do the recvmsg() -> 0 and detect the shutdown.
> > >
> > > Fixes: 04919bed948dc ("tcp: Introduce tcp_read_skb()")
> > > Reviewed-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
> > > Signed-off-by: John Fastabend <john.fastabend@xxxxxxxxx>
> > > ---
> > > net/core/skmsg.c | 11 ++++++++++-
> > > 1 file changed, 10 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/net/core/skmsg.c b/net/core/skmsg.c
> > > index bcd45a99a3db..08be5f409fb8 100644
> > > --- a/net/core/skmsg.c
> > > +++ b/net/core/skmsg.c
> > > @@ -1199,12 +1199,21 @@ static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb)
> > > static void sk_psock_verdict_data_ready(struct sock *sk)
> > > {
> > > struct socket *sock = sk->sk_socket;
> > > + int copied;
> > >
> > > trace_sk_data_ready(sk);
> > >
> > > if (unlikely(!sock || !sock->ops || !sock->ops->read_skb))
> > > return;
> > > - sock->ops->read_skb(sk, sk_psock_verdict_recv);
> > > + copied = sock->ops->read_skb(sk, sk_psock_verdict_recv);
> > > + if (copied >= 0) {
> > > + struct sk_psock *psock;
> > > +
> > > + rcu_read_lock();
> > > + psock = sk_psock(sk);
> > > + psock->saved_data_ready(sk);
> > > + rcu_read_unlock();
> > > + }
> > > }
> > >
> > > void sk_psock_start_verdict(struct sock *sk, struct sk_psock *psock)
> > > --
> > > 2.33.0
> > >
> >
> > It seems psock could be NULL here, right ?
> >
> > What do you think if I submit the following fix ?
> >
> > diff --git a/net/core/skmsg.c b/net/core/skmsg.c
> > index a9060e1f0e4378fa47cfd375b4729b5b0a9f54ec..a29508e1ff3568583263b9307f7b1a0e814ba76d
> > 100644
> > --- a/net/core/skmsg.c
> > +++ b/net/core/skmsg.c
> > @@ -1210,7 +1210,8 @@ static void sk_psock_verdict_data_ready(struct sock *sk)
> >
> > rcu_read_lock();
> > psock = sk_psock(sk);
> > - psock->saved_data_ready(sk);
> > + if (psock)
> > + psock->saved_data_ready(sk);
> > rcu_read_unlock();
> > }
> > }
>
> Yes please do presumably this is plausible if user delete map entry while
> data is being sent and we get a race. We don't have any tests for this
> in our CI though because we never delete socks after adding them and
> rely on the sock close. This shouldn't happen in that path because of the
> data_ready is blocked on SOCK_DEAD flag iirc.
>
> I'll think if we can add some stress test to add map update/delete in
> a tight loop with live socket sending/receiving traffic.
>
> Thanks
I can also submit it if its easier just let me know.
