[PATCH V1 1/1] serial: 8250_fintek: Fix crash with baud rate B0

[Ji-Ze Hong (Peter Hong)]

The 8250_fintek.c is support the Fintek F81866/F81216 with dynamic clock.
But It'll generate "division by zero" exception and crash in
fintek_8250_set_termios() with baud rate 0 on baudrate_table[i] % baud.

It can be tested with following C code:

        ...
        struct termios options;

        tcgetattr(fd, &options);
        ...
        options.c_cflag = CS8 | CREAD; /* baud rate 0 */
        tcsetattr(fd, TCSANOW, &options);
        tcflush(fd, TCIOFLUSH);

Fixes: 195638b6d44f ("serial: 8250_fintek: UART dynamic clocksource on Fintek 
F81866")
Reported-by: Lukas Redlinger <rel+ker...@agilox.net>
Cc: Lukas Redlinger <rel+ker...@agilox.net>
Signed-off-by: Ji-Ze Hong (Peter Hong) <hpeter+linux_ker...@gmail.com>
---
 drivers/tty/serial/8250/8250_fintek.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_fintek.c 
b/drivers/tty/serial/8250/8250_fintek.c
index c41cbb52f1fe..3d66c2c0d7ee 100644
--- a/drivers/tty/serial/8250/8250_fintek.c
+++ b/drivers/tty/serial/8250/8250_fintek.c
@@ -312,6 +312,13 @@ void fintek_8250_set_termios(struct uart_port *port, 
struct ktermios *termios,
                        F81866_UART_CLK_14_769MHZ, F81866_UART_CLK_18_432MHZ,
                        F81866_UART_CLK_24MHZ };
 
+       /*
+        * We'll use serial8250_do_set_termios() for baud = 0, otherwise It'll
+        * crash on baudrate_table[i] % baud with "division by zero".
+        */
+       if (!baud)
+               goto exit;
+
        switch (pdata->pid) {
        case CHIP_ID_F81216H:
                reg = RS485;
@@ -324,8 +331,7 @@ void fintek_8250_set_termios(struct uart_port *port, struct 
ktermios *termios,
                dev_warn(port->dev,
                        "%s: pid: %x Not support. use default set_termios.\n",
                        __func__, pdata->pid);
-               serial8250_do_set_termios(port, termios, old);
-               return;
+               goto exit;
        }
 
        for (i = 0; i < ARRAY_SIZE(baudrate_table); ++i) {
@@ -353,6 +359,7 @@ void fintek_8250_set_termios(struct uart_port *port, struct 
ktermios *termios,
                tty_termios_encode_baud_rate(termios, baud, baud);
        }
 
+exit:
        serial8250_do_set_termios(port, termios, old);
 }
 
-- 
2.7.4