Re: [PATCH] MMC: core: cap MMC card timeouts at 2 seconds.

[Torne (Richard Coles)]

On 31 May 2012 11:00, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
> Hi Richard,
>
> On 29 May 2012 17:02, Torne (Richard Coles) <torne@xxxxxxxxxx> wrote:
>> From: "Torne (Richard Coles)" <torne@xxxxxxxxxx>
>>
>> MMC CSD info can specify very large, ridiculous timeouts, big enough to
>> overflow timeout_ns on 32-bit machines. This can result in the card
>> timing out on every operation because the wrapped timeout value is far
>> too small.
>>
>> Fix the overflow by capping the result at 2 seconds.  Cards specifying
>> longer timeouts are almost certainly insane, and host controllers
>> generally cannot support timeouts that long in any case.
>>
>> 2 seconds should be plenty of time for any card to actually function;
>> the timeout calculation code is already using 1 second as a "worst case"
>> timeout for cards running in SPI mode.
>>
>> Signed-off-by: Torne (Richard Coles) <torne@xxxxxxxxxx>
>> ---
>>  drivers/mmc/core/core.c |   11 ++++++++++-
>>  1 files changed, 10 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
>> index 0b6141d..3b4a9fc 100644
>> --- a/drivers/mmc/core/core.c
>> +++ b/drivers/mmc/core/core.c
>> @@ -512,7 +512,16 @@ void mmc_set_data_timeout(struct mmc_data *data, const struct mmc_card *card)
>>        if (data->flags & MMC_DATA_WRITE)
>>                mult <<= card->csd.r2w_factor;
>>
>> -       data->timeout_ns = card->csd.tacc_ns * mult;
>> +       /*
>> +        * The timeout in nanoseconds may overflow with some cards. Cap it at
>> +        * two seconds both to avoid the overflow and also because host
>> +        * controllers cannot generally generate timeouts that long anyway.
>> +        */
>> +       if (card->csd.tacc_ns <= (2 * NSEC_PER_SEC) / mult)
>> +               data->timeout_ns = card->csd.tacc_ns * mult;
>> +       else
>> +               data->timeout_ns = 2 * NSEC_PER_SEC;
>> +
>
> The above looks OK to me, although if doing this for tacc_ns we might
> want to do this for tacc_clks as well. Could we include that is this
> patch as well?

timeout_clks can't overflow, that I can see: the highest possible
value for tacc_clks is 25500 (it's an 8 bit field specified in
100-clock increments) and the highest mult is 12800 (r2w_factor only
goes up to 128). This only makes 0x13747800 :)

>>        data->timeout_clks = card->csd.tacc_clks * mult;
>>
>>        /*
>> --
>> 1.7.7.3
>>
>> --
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>
> Kind regards
> Ulf Hansson



-- 
Torne (Richard Coles)
torne@xxxxxxxxxx
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