[PATCH net v5 1/2] bpf, skmsg: fix verdict sk_data_ready racing with ktls rx

[Xingwang Xiang <v3rdant.xiang@gmail.com>]

sk_psock_strp_data_ready() already checks tls_sw_has_ctx_rx() and
defers to psock->saved_data_ready when a TLS RX context is present,
avoiding a conflict with the TLS strparser's ownership of the receive
queue (commit e91de6afa81c, "bpf: Fix running sk_skb program types
with ktls").

sk_psock_verdict_data_ready() has no equivalent guard.  When a socket
is inserted into a sockmap (BPF_SK_SKB_VERDICT) before TLS RX is
configured, tls_sw_strparser_arm() saves sk_psock_verdict_data_ready
as rx_ctx->saved_data_ready.  On data arrival:

  tls_data_ready -> tls_strp_data_ready -> tls_rx_msg_ready
    -> saved_data_ready() = sk_psock_verdict_data_ready()
      -> tcp_read_skb() drains sk_receive_queue via __skb_unlink()
         without calling tcp_eat_skb(), so copied_seq is not advanced.

tls_strp_msg_load() then finds tcp_inq() >= full_len (stale), calls
tcp_recv_skb() on the now-empty queue, hits WARN_ON_ONCE(!first), and
returns with rx_ctx->strp.anchor.frag_list pointing at a psock-owned
(potentially freed) skb.  tls_decrypt_sg() subsequently walks that
frag_list: use-after-free.

Apply the same fix as sk_psock_strp_data_ready(): if a TLS RX context
is present, call psock->saved_data_ready (sock_def_readable) to wake
recv() waiters and return immediately, leaving the receive queue
untouched.  TLS retains sole ownership of the queue and decrypts the
record normally through tls_sw_recvmsg().

Signed-off-by: Xingwang Xiang <v3rdant.xiang@gmail.com>
---
 net/core/skmsg.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index 6187a83bd..e1850caf1 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -1268,12 +1268,19 @@ static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb)
 static void sk_psock_verdict_data_ready(struct sock *sk)
 {
 	const struct proto_ops *ops = NULL;
+	struct sk_psock *psock;
 	struct socket *sock;
 	int copied;
 
 	trace_sk_data_ready(sk);
 
 	rcu_read_lock();
+	psock = sk_psock(sk);
+	if (psock && tls_sw_has_ctx_rx(sk)) {
+		psock->saved_data_ready(sk);
+		rcu_read_unlock();
+		return;
+	}
 	sock = READ_ONCE(sk->sk_socket);
 	if (likely(sock))
 		ops = READ_ONCE(sock->ops);
@@ -1283,8 +1290,6 @@ static void sk_psock_verdict_data_ready(struct sock *sk)
 
 	copied = ops->read_skb(sk, sk_psock_verdict_recv);
 	if (copied >= 0) {
-		struct sk_psock *psock;
-
 		rcu_read_lock();
 		psock = sk_psock(sk);
 		if (psock)