linux-kernel - Re: [PATCH 9/9] serial: xuartps: Fix out-of-bounds access through DT alias

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Date:   Tue, 20 Feb 2018 12:27:28 +0100
From:   Michal Simek <michal.simek@...inx.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Michal Simek <michal.simek@...inx.com>
CC:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Barry Song <baohua@...nel.org>,
        Vineet Gupta <vgupta@...opsys.com>,
        Jiri Slaby <jslaby@...e.com>, <linux-serial@...r.kernel.org>,
        arcml <linux-snps-arc@...ts.infradead.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 9/9] serial: xuartps: Fix out-of-bounds access through DT
 alias

On 20.2.2018 11:38, Geert Uytterhoeven wrote:
> Hi Michal,
> 
> On Tue, Feb 20, 2018 at 11:22 AM, Michal Simek <michal.simek@...inx.com> wrote:
>> On 20.2.2018 10:40, Geert Uytterhoeven wrote:
>>> The cdns_uart_port[] array is indexed using a value derived from the
>>> "serialN" alias in DT, which may lead to an out-of-bounds access.
>>>
>>> Fix this by adding a range check.
>>>
>>> Fixes: 1f118c02a1819856 ("serial: xuartps: Fix out-of-bounds access through DT alias")
>>
>> I didn't find this sha1 - patch name is this one.
> 
> Bummer, I totally screwed up my scripting...
> 
> Fixes: 928e9263492069ee ("tty: xuartps: Initialize ports according to aliases")
> 
>>> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
>>> ---
>>>  drivers/tty/serial/xilinx_uartps.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
>>> index b9b2bc76bcac606c..abcb4d09a2d866d0 100644
>>> --- a/drivers/tty/serial/xilinx_uartps.c
>>> +++ b/drivers/tty/serial/xilinx_uartps.c
>>> @@ -1110,7 +1110,7 @@ static struct uart_port *cdns_uart_get_port(int id)
>>>       struct uart_port *port;
>>>
>>>       /* Try the given port id if failed use default method */
>>> -     if (cdns_uart_port[id].mapbase != 0) {
>>> +     if (id < CDNS_UART_NR_PORTS && cdns_uart_port[id].mapbase != 0) {
>>>               /* Find the next unused port */
>>>               for (id = 0; id < CDNS_UART_NR_PORTS; id++)
>>>                       if (cdns_uart_port[id].mapbase == 0)
>>>
>>
>> Below should be better fix for this driver.
> 
> I considered that, too, but...
> 
>> --- a/drivers/tty/serial/xilinx_uartps.c
>> +++ b/drivers/tty/serial/xilinx_uartps.c
>> @@ -1109,6 +1109,9 @@ static struct uart_port *cdns_uart_get_port(int id)
>>  {
>>         struct uart_port *port;
>>
>> +       if (id >= CDNS_UART_NR_PORTS)
>> +               return NULL;
>> +
>>         /* Try the given port id if failed use default method */
>>         if (cdns_uart_port[id].mapbase != 0) {
>>                 /* Find the next unused port */
>> @@ -1117,9 +1120,6 @@ static struct uart_port *cdns_uart_get_port(int id)
>>                                 break;
>>         }
>>
>> -       if (id >= CDNS_UART_NR_PORTS)
>> -               return NULL;
>> -
> 
> ... the above check cannot be removed, as it is needed to support the loop
> above to find an unused port.

You are right.
I have checked 4 patches I have sent in past which didn't reach mainline
(probably because of RFC)
Take a look at
https://www.spinics.net/lists/linux-serial/msg27106.html

I have removed cdns_uart_port array completely there.

Thanks,
Michal