netdev - [PATCH bpf-next v2 04/11] tcp_bpf: Don't let child socket inherit parent protocol ops on copy

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Date:   Fri, 10 Jan 2020 11:50:20 +0100
From:   Jakub Sitnicki <jakub@...udflare.com>
To:     bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org, kernel-team@...udflare.com,
        Eric Dumazet <edumazet@...gle.com>,
        John Fastabend <john.fastabend@...il.com>,
        Lorenz Bauer <lmb@...udflare.com>,
        Martin KaFai Lau <kafai@...com>
Subject: [PATCH bpf-next v2 04/11] tcp_bpf: Don't let child socket inherit parent protocol ops on copy

Prepare for cloning listening sockets that have their protocol callbacks
overridden by sk_msg. Child sockets must not inherit parent callbacks that
access state stored in sk_user_data owned by the parent.

Restore the child socket protocol callbacks before the it gets hashed and
any of the callbacks can get invoked.

Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
---
 include/net/tcp.h        |  1 +
 net/ipv4/tcp_bpf.c       | 13 +++++++++++++
 net/ipv4/tcp_minisocks.c |  2 ++
 3 files changed, 16 insertions(+)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 9dd975be7fdf..7cbf9465bb10 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -2181,6 +2181,7 @@ int tcp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 		    int nonblock, int flags, int *addr_len);
 int __tcp_bpf_recvmsg(struct sock *sk, struct sk_psock *psock,
 		      struct msghdr *msg, int len, int flags);
+void tcp_bpf_clone(const struct sock *sk, struct sock *child);
 
 /* Call BPF_SOCK_OPS program that returns an int. If the return value
  * is < 0, then the BPF op failed (for example if the loaded BPF
diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
index f6c83747c71e..6f96320fb7cf 100644
--- a/net/ipv4/tcp_bpf.c
+++ b/net/ipv4/tcp_bpf.c
@@ -586,6 +586,19 @@ static void tcp_bpf_close(struct sock *sk, long timeout)
 	saved_close(sk, timeout);
 }
 
+/* If a child got cloned from a listening socket that had tcp_bpf
+ * protocol callbacks installed, we need to restore the callbacks to
+ * the default ones because the child does not inherit the psock state
+ * that tcp_bpf callbacks expect.
+ */
+void tcp_bpf_clone(const struct sock *sk, struct sock *newsk)
+{
+	struct proto *prot = newsk->sk_prot;
+
+	if (prot->recvmsg == tcp_bpf_recvmsg)
+		newsk->sk_prot = sk->sk_prot_creator;
+}
+
 enum {
 	TCP_BPF_IPV4,
 	TCP_BPF_IPV6,
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index ad3b56d9fa71..c8274371c3d0 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -548,6 +548,8 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
 	newtp->fastopen_req = NULL;
 	RCU_INIT_POINTER(newtp->fastopen_rsk, NULL);
 
+	tcp_bpf_clone(sk, newsk);
+
 	__TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS);
 
 	return newsk;
-- 
2.24.1