firmware_loader: prevent integer overflow in firmware_loading_timeout()

In firmware_loading_timeout(), *int* result of __firmware_loading_timeout()
multiplied by HZ might overflow before being implicitly cast to *long* when
being returned. Rewrite the function using check_mul_overflow() and capping
the result at LONG_MAX on actual overflow...

Found by Linux Verification Center (linuxtesting.org) with the Svace static
analysis tool.

Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Cc: stable@vger.kernel.org
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>

Author: Sergey Shtylyov

drivers/base/firmware_loader/fallback.c

@@ -35,8 +35,13 @@ void fw_fallback_set_default_timeout(void)
 
 static long firmware_loading_timeout(void)
 {
-	return __firmware_loading_timeout() > 0 ?
-		__firmware_loading_timeout() * HZ : MAX_JIFFY_OFFSET;
+	long timeout;
+
+	if (__firmware_loading_timeout() <= 0)
+		return MAX_JIFFY_OFFSET;
+	if (check_mul_overflow(__firmware_loading_timeout(), HZ, &timeout))
+		return LONG_MAX;
+	return timeout;
 }
 
 static inline int fw_sysfs_wait_timeout(struct fw_priv *fw_priv,  long timeout)