smb: client: fix TCP timers deadlock after rmmod with non-init_net ns

Commit ef7134c ("smb: client: Fix use-after-free of network namespace.")
fixed a netns UAF by manually enabled socket refcounting
(sk->sk_net_refcnt=1 and sock_inuse_add(net, 1)).

The reason the patch worked was because we now hold references to the
netns (get_net_track() gets a ref internally) and they're released
properly (internally, on __sk_destruct()), but only because
sk->sk_net_refcnt was set.

Problem:
(this happens regardless of CONFIG_NET_NS_REFCNT_TRACKER)

Manually setting sk->sk_net_refcnt=1 *after* socket creation is not only
out of cifs scope, but also technically wrong -- it's set conditionally
based on user (=1) vs kernel (=0) sockets.  And net/ implementations
seem to base their user vs kernel space operations on it.

e.g. upon TCP socket close, the TCP timers are not cleared because
sk->sk_net_refcnt=1:
(cf. commit 151c9c7 ("tcp: properly terminate timers for kernel sockets"))

net/ipv4/tcp.c:
    void tcp_close(struct sock *sk, long timeout)
    {
    	lock_sock(sk);
    	__tcp_close(sk, timeout);
    	release_sock(sk);
    	if (!sk->sk_net_refcnt)
    		inet_csk_clear_xmit_timers_sync(sk);
    	sock_put(sk);
    }

Which will throw a lockdep warning and then, as expected, deadlock on
tcp_write_timer().

A way to reproduce this is by running the reproducer from ef7134c
and then 'rmmod cifs'.  A few seconds later, the deadlock/lockdep
warning shows up.

Fix:
We shouldn't mess with socket internals ourselves, so deal the best way
we can -- keep an extra netns reference for server->ssocket and drop it
when it's released.  This ensures that the netns still exists whenever
we need to create/destroy server->ssocket, but is not directly tied to
it.

Also change __sock_create() to sock_create_kern() for explicitness.

Signed-off-by: Enzo Matsumiya <ematsumiya@suse.de>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/client/connect.c

@@ -987,9 +987,13 @@ clean_demultiplex_info(struct TCP_Server_Info *server)
 	msleep(125);
 	if (cifs_rdma_enabled(server))
 		smbd_destroy(server);
+
 	if (server->ssocket) {
 		sock_release(server->ssocket);
 		server->ssocket = NULL;
+
+		/* Release netns reference for the socket. */
+		put_net(cifs_net_ns(server));
 	}
 
 	if (!list_empty(&server->pending_mid_q)) {
@@ -1037,6 +1041,7 @@ clean_demultiplex_info(struct TCP_Server_Info *server)
 		 */
 	}
 
+	/* Release netns reference for this server. */
 	put_net(cifs_net_ns(server));
 	kfree(server->leaf_fullpath);
 	kfree(server);
@@ -1713,6 +1718,8 @@ cifs_get_tcp_session(struct smb3_fs_context *ctx,
 
 	tcp_ses->ops = ctx->ops;
 	tcp_ses->vals = ctx->vals;
+
+	/* Grab netns reference for this server. */
 	cifs_set_net_ns(tcp_ses, get_net(current->nsproxy->net_ns));
 
 	tcp_ses->conn_id = atomic_inc_return(&tcpSesNextId);
@@ -1844,6 +1851,7 @@ cifs_get_tcp_session(struct smb3_fs_context *ctx,
 out_err_crypto_release:
 	cifs_crypto_secmech_release(tcp_ses);
 
+	/* Release netns reference for this server. */
 	put_net(cifs_net_ns(tcp_ses));
 
 out_err:
@@ -1852,8 +1860,10 @@ cifs_get_tcp_session(struct smb3_fs_context *ctx,
 			cifs_put_tcp_session(tcp_ses->primary_server, false);
 		kfree(tcp_ses->hostname);
 		kfree(tcp_ses->leaf_fullpath);
-		if (tcp_ses->ssocket)
+		if (tcp_ses->ssocket) {
 			sock_release(tcp_ses->ssocket);
+			put_net(cifs_net_ns(tcp_ses));
+		}
 		kfree(tcp_ses);
 	}
 	return ERR_PTR(rc);
@@ -3131,20 +3141,20 @@ generic_ip_connect(struct TCP_Server_Info *server)
 		socket = server->ssocket;
 	} else {
 		struct net *net = cifs_net_ns(server);
-		struct sock *sk;
 
-		rc = __sock_create(net, sfamily, SOCK_STREAM,
-				   IPPROTO_TCP, &server->ssocket, 1);
+		rc = sock_create_kern(net, sfamily, SOCK_STREAM, IPPROTO_TCP, &server->ssocket);
 		if (rc < 0) {
 			cifs_server_dbg(VFS, "Error %d creating socket\n", rc);
 			return rc;
 		}
 
-		sk = server->ssocket->sk;
-		__netns_tracker_free(net, &sk->ns_tracker, false);
-		sk->sk_net_refcnt = 1;
-		get_net_track(net, &sk->ns_tracker, GFP_KERNEL);
-		sock_inuse_add(net, 1);
+		/*
+		 * Grab netns reference for the socket.
+		 *
+		 * It'll be released here, on error, or in clean_demultiplex_info() upon server
+		 * teardown.
+		 */
+		get_net(net);
 
 		/* BB other socket options to set KEEPALIVE, NODELAY? */
 		cifs_dbg(FYI, "Socket created\n");
@@ -3158,8 +3168,10 @@ generic_ip_connect(struct TCP_Server_Info *server)
 	}
 
 	rc = bind_socket(server);
-	if (rc < 0)
+	if (rc < 0) {
+		put_net(cifs_net_ns(server));
 		return rc;
+	}
 
 	/*
 	 * Eventually check for other socket options to change from
@@ -3196,6 +3208,7 @@ generic_ip_connect(struct TCP_Server_Info *server)
 	if (rc < 0) {
 		cifs_dbg(FYI, "Error %d connecting to server\n", rc);
 		trace_smb3_connect_err(server->hostname, server->conn_id, &server->dstaddr, rc);
+		put_net(cifs_net_ns(server));
 		sock_release(socket);
 		server->ssocket = NULL;
 		return rc;
@@ -3204,6 +3217,9 @@ generic_ip_connect(struct TCP_Server_Info *server)
 	if (sport == htons(RFC1001_PORT))
 		rc = ip_rfc1001_connect(server);
 
+	if (rc < 0)
+		put_net(cifs_net_ns(server));
+
 	return rc;
 }