ksmbd: Prevent integer overflow in calculation of deadtime

The user can set any value for 'deadtime'. This affects the arithmetic
expression 'req->deadtime * SMB_ECHO_INTERVAL', which is subject to
overflow. The added check makes the server behavior more predictable.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 0626e66 ("cifsd: add server handler for central processing and tranport layers")
Cc: stable@vger.kernel.org
Signed-off-by: Denis Arefev <arefev@swemel.ru>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/server/transport_ipc.c

@@ -310,7 +310,11 @@ static int ipc_server_config_on_startup(struct ksmbd_startup_request *req)
 	server_conf.signing = req->signing;
 	server_conf.tcp_port = req->tcp_port;
 	server_conf.ipc_timeout = req->ipc_timeout * HZ;
-	server_conf.deadtime = req->deadtime * SMB_ECHO_INTERVAL;
+	if (check_mul_overflow(req->deadtime, SMB_ECHO_INTERVAL,
+					&server_conf.deadtime)) {
+		ret = -EINVAL;
+		goto out;
+	}
 	server_conf.share_fake_fscaps = req->share_fake_fscaps;
 	ksmbd_init_domain(req->sub_auth);
 
@@ -337,6 +341,7 @@ static int ipc_server_config_on_startup(struct ksmbd_startup_request *req)
 	server_conf.bind_interfaces_only = req->bind_interfaces_only;
 	ret |= ksmbd_tcp_set_interfaces(KSMBD_STARTUP_CONFIG_INTERFACES(req),
 					req->ifc_list_sz);
+out:
 	if (ret) {
 		pr_err("Server configuration error: %s %s %s\n",
 		       req->netbios_name, req->server_string,