linux-kernel - [PATCH] MMC: core: cap MMC card timeouts at 2 seconds.

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Date:	Tue, 29 May 2012 10:02:20 +0100
From:	"Torne (Richard Coles)" <torne@...gle.com>
To:	cjb@...top.org
Cc:	linus.walleij@...aro.org, jh80.chung@...sung.com,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
	ben@...adent.org.uk, "Torne (Richard Coles)" <torne@...gle.com>
Subject: [PATCH] MMC: core: cap MMC card timeouts at 2 seconds.

From: "Torne (Richard Coles)" <torne@...gle.com>

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@...gle.com>
---
 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;
+
 	data->timeout_clks = card->csd.tacc_clks * mult;
 
 	/*
-- 
1.7.7.3

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