Martin KaFai Lau dbafd7ddd6 bpf: Add bpf_get_listener_sock(struct bpf_sock *sk) helper
Add a new helper "struct bpf_sock *bpf_get_listener_sock(struct bpf_sock *sk)"
which returns a bpf_sock in TCP_LISTEN state.  It will trace back to
the listener sk from a request_sock if possible.  It returns NULL
for all other cases.

No reference is taken because the helper ensures the sk is
in SOCK_RCU_FREE (where the TCP_LISTEN sock should be in).
Hence, bpf_sk_release() is unnecessary and the verifier does not
allow bpf_sk_release(listen_sk) to be called either.

The following is also allowed because the bpf_prog is run under
rcu_read_lock():

	sk = bpf_sk_lookup_tcp();
	/* if (!sk) { ... } */
	listen_sk = bpf_get_listener_sock(sk);
	/* if (!listen_sk) { ... } */
	bpf_sk_release(sk);
	src_port = listen_sk->src_port; /* Allowed */

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2019-03-13 12:04:35 -07:00
2019-02-15 09:12:28 -08:00
2019-03-05 10:00:35 -08:00
2019-02-20 09:42:52 -08:00
2019-02-21 11:41:19 +00:00
2019-03-03 15:21:29 -08:00

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.
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