On 29/05/12 05:32, Ben Hutchings wrote: > On Mon, 2012-05-28 at 18:31 +0100, Torne (Richard Coles) 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. > > Needs a 'Signed-off-by'. > >> --- >> 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; > > We clearly need to guard against overflow here, and this is the correct > way to clamp the multiplication. I can't speak as to whether 2 seconds > is the right limit. The host controllers I have looked at have a limit of around 2.5 seconds. But why not just use the size of the type as the limit? e.g. if (card->csd.tacc_ns <= UINT_MAX / mult) data->timeout_ns = card->csd.tacc_ns * mult; else data->timeout_ns = UINT_MAX; > > Ben. > >> data->timeout_clks = card->csd.tacc_clks * mult; >> >> /* > -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
