bpf: tcp: Do not limit cb_flags when creating child sk from listen sk

The commit 0813a841 ("bpf: tcp: Allow bpf prog to write and parse TCP header option")
unnecessarily introduced bpf_skops_init_child() which limited the child
sk from inheriting all bpf_sock_ops_cb_flags of the listen sk.  That
breaks existing user expectation.

This patch removes the bpf_skops_init_child() and just allows
sock_copy() to do its job to copy everything from listen sk to
the child sk.

Fixes: 0813a841 ("bpf: tcp: Allow bpf prog to write and parse TCP header option")
Reported-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201002013448.2542025-1-kafai@fb.com

include/net/tcp.h

@@ -2228,34 +2228,6 @@ int __tcp_bpf_recvmsg(struct sock *sk, struct sk_psock *psock,
 #endif /* CONFIG_NET_SOCK_MSG */
 
 #ifdef CONFIG_CGROUP_BPF
-/* Copy the listen sk's HDR_OPT_CB flags to its child.
- *
- * During 3-Way-HandShake, the synack is usually sent from
- * the listen sk with the HDR_OPT_CB flags set so that
- * bpf-prog will be called to write the BPF hdr option.
- *
- * In fastopen, the child sk is used to send synack instead
- * of the listen sk.  Thus, inheriting the HDR_OPT_CB flags
- * from the listen sk gives the bpf-prog a chance to write
- * BPF hdr option in the synack pkt during fastopen.
- *
- * Both fastopen and non-fastopen child will inherit the
- * HDR_OPT_CB flags to keep the bpf-prog having a consistent
- * behavior when deciding to clear this cb flags (or not)
- * during the PASSIVE_ESTABLISHED_CB.
- *
- * In the future, other cb flags could be inherited here also.
- */
-static inline void bpf_skops_init_child(const struct sock *sk,
-					struct sock *child)
-{
-	tcp_sk(child)->bpf_sock_ops_cb_flags =
-		tcp_sk(sk)->bpf_sock_ops_cb_flags &
-		(BPF_SOCK_OPS_PARSE_ALL_HDR_OPT_CB_FLAG |
-		 BPF_SOCK_OPS_PARSE_UNKNOWN_HDR_OPT_CB_FLAG |
-		 BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG);
-}
-
 static inline void bpf_skops_init_skb(struct bpf_sock_ops_kern *skops,
 				      struct sk_buff *skb,
 				      unsigned int end_offset)
@@ -2264,11 +2236,6 @@ static inline void bpf_skops_init_skb(struct bpf_sock_ops_kern *skops,
 	skops->skb_data_end = skb->data + end_offset;
 }
 #else
-static inline void bpf_skops_init_child(const struct sock *sk,
-					struct sock *child)
-{
-}
-
 static inline void bpf_skops_init_skb(struct bpf_sock_ops_kern *skops,
 				      struct sk_buff *skb,
 				      unsigned int end_offset)

net/ipv4/tcp_minisocks.c

@@ -548,7 +548,6 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
 	newtp->fastopen_req = NULL;
 	RCU_INIT_POINTER(newtp->fastopen_rsk, NULL);
 
-	bpf_skops_init_child(sk, newsk);
 	tcp_bpf_clone(sk, newsk);
 
 	__TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS);