[PATCH bpf v3 2/2] bpf, sockmap: sk_prot needs inuse_idx set for proc stats

[John Fastabend <john.fastabend@xxxxxxxxx>]

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@xxxxxxxxx>
---
 net/core/sock_map.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 60decd6420ca..27bdf768aa8c 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -185,10 +185,19 @@ static void sock_map_unref(struct sock *sk, void *link_raw)
 
 static int sock_map_init_proto(struct sock *sk, struct sk_psock *psock)
 {
+	int err;
+#ifdef CONFIG_PROC_FS
+	int idx = sk->sk_prot->inuse_idx;
+#endif
 	if (!sk->sk_prot->psock_update_sk_prot)
 		return -EINVAL;
 	psock->psock_update_sk_prot = sk->sk_prot->psock_update_sk_prot;
-	return sk->sk_prot->psock_update_sk_prot(sk, psock, false);
+	err = sk->sk_prot->psock_update_sk_prot(sk, psock, false);
+#ifdef CONFIG_PROC_FS
+	if (!err)
+		sk->sk_prot->inuse_idx = idx;
+#endif
+	return err;
 }
 
 static struct sk_psock *sock_map_psock_get_checked(struct sock *sk)
-- 
2.25.1