bpf: sockmap, fix introduced strparser recursive lock

Originally there was a race where removing a psock from the sock map while
it was also receiving an skb and calling sk_psock_data_ready(). It was
possible the removal code would NULL/set the data_ready callback while
concurrently calling the hook from receive path. The fix was to wrap the
access in sk_callback_lock to ensure the saved_data_ready pointer didn't
change under us. There was some discussion around doing a larger change
to ensure we could use READ_ONCE/WRITE_ONCE over the callback, but that
was for *next kernels not stable fixes.

But, we unfortunately introduced a regression with the fix because there
is another path into this code (that didn't have a test case) through
the stream parser. The stream parser runs with the lower lock which means
we get the following splat and lock up.

 ============================================
 WARNING: possible recursive locking detected
 6.10.0-rc2 torvalds#59 Not tainted
 --------------------------------------------
 test_sockmap/342 is trying to acquire lock:
 ffff888007a87228 (clock-AF_INET){++--}-{2:2}, at:
 sk_psock_skb_ingress_enqueue (./include/linux/skmsg.h:467
 net/core/skmsg.c:555)

 but task is already holding lock:
 ffff888007a87228 (clock-AF_INET){++--}-{2:2}, at:
 sk_psock_strp_data_ready (net/core/skmsg.c:1120)

To fix ensure we do not grap lock when we reach this code through the
strparser.

Fixes: 6648e61 ("bpf, skmsg: Fix NULL pointer dereference in sk_psock_skb_ingress_enqueue")
Reported-by: Vincent Whitchurch <[email protected]>
Signed-off-by: John Fastabend <[email protected]>

include/linux/skmsg.h

@@ -461,13 +461,18 @@ static inline void sk_psock_put(struct sock *sk, struct sk_psock *psock)
 		sk_psock_drop(sk, psock);
 }
 
-static inline void sk_psock_data_ready(struct sock *sk, struct sk_psock *psock)
+static inline void __sk_psock_data_ready(struct sock *sk, struct sk_psock *psock)
 {
-	read_lock_bh(&sk->sk_callback_lock);
 	if (psock->saved_data_ready)
 		psock->saved_data_ready(sk);
 	else
 		sk->sk_data_ready(sk);
+}
+
+static inline void sk_psock_data_ready(struct sock *sk, struct sk_psock *psock)
+{
+	read_lock_bh(&sk->sk_callback_lock);
+	__sk_psock_data_ready(sk, psock);
 	read_unlock_bh(&sk->sk_callback_lock);
 }
 

net/core/skmsg.c

@@ -552,7 +552,10 @@ static int sk_psock_skb_ingress_enqueue(struct sk_buff *skb,
 	msg->skb = skb;
 
 	sk_psock_queue_msg(psock, msg);
-	sk_psock_data_ready(sk, psock);
+	if (skb_bpf_strparser(skb))
+		__sk_psock_data_ready(sk, psock);
+	else
+		sk_psock_data_ready(sk, psock);
 	return copied;
 }