On Sun, Jan 12, 2020 at 12:48 AM CET, John Fastabend wrote:

Jakub Sitnicki wrote:

quoted

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@cloudflare.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;
+}
+

^^^^ probably needs to go into tcp.h wrapped in ifdef NET_SOCK_MSG with
a stub for ifndef NET_SOCK_MSG case.

Looks like build bot also caught this.

Oops, I need to add NET_SOCK_MSG to my build matrix :-)