diff --git a/drivers/serial/mfd.c b/drivers/serial/mfd.c
index 5dff45c76d32c5f026dc1ae408166a4f5e9ac6d2..ad35130cd8a096f27281111c9fb134a9425deac5 100644
--- a/drivers/serial/mfd.c
+++ b/drivers/serial/mfd.c
@@ -172,6 +172,9 @@ static ssize_t port_show_regs(struct file *file, char __user *user_buf,
 	len += snprintf(buf + len, HSU_REGS_BUFSIZE - len,
 			"DIV: \t\t0x%08x\n", serial_in(up, UART_DIV));
 
+	if (len > HSU_REGS_BUFSIZE)
+		len = HSU_REGS_BUFSIZE;
+
 	ret =  simple_read_from_buffer(user_buf, count, ppos, buf, len);
 	kfree(buf);
 	return ret;
@@ -219,6 +222,9 @@ static ssize_t dma_show_regs(struct file *file, char __user *user_buf,
 	len += snprintf(buf + len, HSU_REGS_BUFSIZE - len,
 			"D0TSR: \t\t0x%08x\n", chan_readl(chan, HSU_CH_D3TSR));
 
+	if (len > HSU_REGS_BUFSIZE)
+		len = HSU_REGS_BUFSIZE;
+
 	ret =  simple_read_from_buffer(user_buf, count, ppos, buf, len);
 	kfree(buf);
 	return ret;