[PATCH bpf v4 1/2] bpf: fix recursive lock when verdict program return SK_PASS

[Jiayuan Chen <mrpre@163.com>]

When the stream_verdict program returns SK_PASS, it places the received skb
into its own receive queue, but a recursive lock eventually occurs, leading
to an operating system deadlock. This issue has been present since v6.9.

'''
sk_psock_strp_data_ready
    write_lock_bh(&sk->sk_callback_lock)
    strp_data_ready
      strp_read_sock
        read_sock -> tcp_read_sock
          strp_recv
            cb.rcv_msg -> sk_psock_strp_read
              # now stream_verdict return SK_PASS without peer sock assign
              __SK_PASS = sk_psock_map_verd(SK_PASS, NULL)
              sk_psock_verdict_apply
                sk_psock_skb_ingress_self
                  sk_psock_skb_ingress_enqueue
                    sk_psock_data_ready
                      read_lock_bh(&sk->sk_callback_lock) <= dead lock

'''

This topic has been discussed before, but it has not been fixed.
Previous discussion:
https://lore.kernel.org/all/6684a5864ec86_403d20898@john.notmuch

Fixes: 6648e613226e ("bpf, skmsg: Fix NULL pointer dereference in sk_psock_skb_ingress_enqueue")
Reported-by: Vincent Whitchurch <vincent.whitchurch@datadoghq.com>
Signed-off-by: Jiayuan Chen <mrpre@163.com>
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
 net/core/skmsg.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index b1dcbd3be89e..e90fbab703b2 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -1117,9 +1117,9 @@ static void sk_psock_strp_data_ready(struct sock *sk)
 		if (tls_sw_has_ctx_rx(sk)) {
 			psock->saved_data_ready(sk);
 		} else {
-			write_lock_bh(&sk->sk_callback_lock);
+			read_lock_bh(&sk->sk_callback_lock);
 			strp_data_ready(&psock->strp);
-			write_unlock_bh(&sk->sk_callback_lock);
+			read_unlock_bh(&sk->sk_callback_lock);
 		}
 	}
 	rcu_read_unlock();
-- 
2.43.5