linux-kernel - Re: [PATCH] watchdog: dw_wdt: Fix buffer overflow when get timeout

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Date:   Tue, 28 Jun 2022 22:30:57 +0800
From:   Schspa Shi <schspa@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     wim@...ux-watchdog.org, linux-watchdog@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] watchdog: dw_wdt: Fix buffer overflow when get timeout

Guenter Roeck <linux@...ck-us.net> writes:

> On 6/27/22 22:45, Schspa Shi wrote:
>> The top_val can be obtained from device-tree, if it is not configured
>> correctly, there will be buffer overflow.
>> Signed-off-by: Schspa Shi <schspa@...il.com>
>> ---
>>   drivers/watchdog/dw_wdt.c | 6 ++++++
>>   1 file changed, 6 insertions(+)
>> diff --git a/drivers/watchdog/dw_wdt.c b/drivers/watchdog/dw_wdt.c
>> index cd578843277e..1f8605c0d712 100644
>> --- a/drivers/watchdog/dw_wdt.c
>> +++ b/drivers/watchdog/dw_wdt.c
>> @@ -155,6 +155,9 @@ static unsigned int dw_wdt_get_min_timeout(struct dw_wdt *dw_wdt)
>>                      break;
>>      }
>>   +  if (WARN_ON_ONCE(idx == DW_WDT_NUM_TOPS))
>> +            idx = DW_WDT_NUM_TOPS - 1;
>> +
> dw_wdt_get_min_timeout() returns the lowest non-0 configurable timeout.
> The  last entry in the timeout array must not be 0, meaning there must
> be at least one entry in the array where the timeout is not 0. Therefore
> this situation can not happen.
>

Yes, I have seen this, you are correct, sorry for the bad patch.

>>      return dw_wdt->timeouts[idx].sec;
>>   }
>>   @@ -178,6 +181,9 @@ static unsigned int dw_wdt_get_timeout(struct dw_wdt
>> *dw_wdt)
>>                      break;
>>      }
>>   +  if (WARN_ON_ONCE(idx == DW_WDT_NUM_TOPS))
>> +            idx = DW_WDT_NUM_TOPS - 1;
>> +
>
> idx is derived from a top_val value written into WDOG_TIMEOUT_RANGE_REG_OFFSET,
> and the value written is derived from an entry in the timeouts array.
> This array contains an entry for each possible top_val. While the array is not
> sorted by top_val, dw_wdt_handle_tops() still guarantees that an entry exists.
>
> I do not see how bad devicetree data can circumvent that. If it does, please
> provide an example and explain.
>

My bad, there is no problem.

> Thanks,
> Guenter


-- 
BRs
Schspa Shi