linux-kernel - [PATCH] 8250_dw: do not int overflow when rate can not be aplied

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Date:   Thu, 11 Jan 2018 14:38:32 +0100
From:   Nuno Goncalves <nunojpg@...il.com>
To:     ed.blake@...drel.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Cc:     Nuno Goncalves <nunojpg@...il.com>
Subject: [PATCH] 8250_dw: do not int overflow when rate can not be aplied

When target_rate is big enough and not permitted in hardware,
then i is looped to UART_DIV_MAX (0xFFFF), and i * max_rate will overflow
(32b signed).

A fix is to quit the loop early enough, as soon as rate < i * min_rate as it
means the rate is not permitted.

This avoids arbitraty rates to be applied. Still in my hardware the max
allowed rate (1500000) is aplied when a higher is requested. This seems a
artifact of clk_round_rate which is not understood by me and independent of
this fix. Might or might not be another bug.

Signed-off-by: Nuno Goncalves <nunojpg@...il.com>
---
 drivers/tty/serial/8250/8250_dw.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 5bb0c42c88dd..a27ea916abbf 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -267,7 +267,13 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios,

 	for (i = 1; i <= UART_DIV_MAX; i++) {
 		rate = clk_round_rate(d->clk, i * target_rate);
-		if (rate >= i * min_rate && rate <= i * max_rate)
+
+		if (rate < i * min_rate) {
+			i = UART_DIV_MAX + 1;
+			break;
+		}
+
+		if (rate <= i * max_rate)
 			break;
 	}
 	if (i <= UART_DIV_MAX) {
-- 
2.11.0