[PATCH bpf, sockmap 2/2] bpf, sockmap: sk_prot needs inuse_idx set for proc stats

[John Fastabend <john.fastabend@gmail.com>]

Proc socket stats use sk_prot->inuse_idx value to record inuse sock stats.
We currently do not set this correctly from sockmap side. The result is
reading sock stats '/proc/net/sockstat' gives incorrect values. The
socket counter is incremented correctly, but because we don't set the
counter correctly when we replace sk_prot we may omit the decrement.

Fixes: 604326b41a6fb ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
 net/core/sock_map.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 60decd6420ca..29e7bae65db5 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -221,7 +221,7 @@ static int sock_map_link(struct bpf_map *map, struct sock *sk)
 	struct bpf_prog *skb_verdict = NULL;
 	struct bpf_prog *msg_parser = NULL;
 	struct sk_psock *psock;
-	int ret;
+	int ret, idx;
 
 	/* Only sockets we can redirect into/from in BPF need to hold
 	 * refs to parser/verdict progs and have their sk_data_ready
@@ -293,9 +293,11 @@ static int sock_map_link(struct bpf_map *map, struct sock *sk)
 	if (msg_parser)
 		psock_set_prog(&psock->progs.msg_parser, msg_parser);

+	idx = sk->sk_prot->inuse_idx;
 	ret = sock_map_init_proto(sk, psock);
 	if (ret < 0)
 		goto out_drop;
+	sk->sk_prot->inuse_idx = idx;
 
 	write_lock_bh(&sk->sk_callback_lock);
 	if (stream_parser && stream_verdict && !psock->saved_data_ready) {
-- 
2.25.1