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bpf: Add bpf_get_listener_sock(struct bpf_sock *sk) helper

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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>
This commit is contained in:
Martin KaFai Lau
2019-03-12 10:23:04 -07:00
committed by Alexei Starovoitov
parent 1b98658968
commit dbafd7ddd6
2 changed files with 31 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
include/uapi/linux/bpf.h
View File

@ -2366,6 +2366,14 @@ union bpf_attr {
* current value is ect (ECN capable). Works with IPv6 and IPv4.
* Return
* 1 if set, 0 if not set.
*
* struct bpf_sock *bpf_get_listener_sock(struct bpf_sock *sk)
* Description
* Return a **struct bpf_sock** pointer in TCP_LISTEN state.
* bpf_sk_release() is unnecessary and not allowed.
* Return
* A **struct bpf_sock** pointer on success, or NULL in
* case of failure.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@ -2465,7 +2473,8 @@ union bpf_attr {
FN(spin_unlock), \
FN(sk_fullsock), \
FN(tcp_sock), \
FN(skb_ecn_set_ce),
FN(skb_ecn_set_ce), \
FN(get_listener_sock),
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call