spi: Prevent unexpected SPI time out due to arithmetic overflow

When reading SPI flash as MTD device, the transfer length is directly passed to the spi driver. If the requested data size exceeds 512KB, it will cause the time out calculation to overflow since transfer length is 32-bit unsigned integer. This issue is resolved by using 64-bit unsigned integer to perform the arithmetic.

Natinst-ReviewBoard-ID 150232
---
Updated the patch to apply to latest spi.c

---
 drivers/spi/spi.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

index 51ad42f..ac889df 100644
@@ -960,7 +960,7 @@ static int spi_transfer_one_message(struct spi_master *master,
 	struct spi_transfer *xfer;
 	bool keep_cs = false;
 	int ret = 0;
-	unsigned long ms = 1;
+	unsigned long long ms = 1;
 	struct spi_statistics *statm = &master->statistics;
 	struct spi_statistics *stats = &msg->spi->statistics;
 

@@ -991,9 +991,13 @@ static int spi_transfer_one_message(struct spi_master *master,
 
 			if (ret > 0) {
 				ret = 0;
-				ms = xfer->len * 8 * 1000 / xfer->speed_hz;
+				ms = 8LL * 1000LL * xfer->len;
+				do_div(ms, xfer->speed_hz);
 				ms += ms + 100; /* some tolerance */
 
+				if (ms > UINT_MAX)
+					ms = UINT_MAX;
+
 				ms = wait_for_completion_timeout(&master->xfer_completion,
 								 msecs_to_jiffies(ms));
 			}

1.7.1

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The patch

spi: Prevent unexpected SPI time out due to arithmetic overflow

has been applied to the spi tree at

git://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git

All being well this means that it will be integrated into the linux-next tree (usually sometime in the next 24 hours) and sent to Linus during the next merge window (or sooner if it is a bug fix), however if problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing and review of the tree, please engage with people reporting problems and send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they should be sent as incremental updates against current git, existing patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying to this mail.

Thanks,
Mark

From: Sien Wu <[email protected]>
Date: Thu, 1 Sep 2016 18:24:29 -0500
Subject: [PATCH] spi: Prevent unexpected SPI time out due to arithmetic
overflow

When reading SPI flash as MTD device, the transfer length is directly passed to the spi driver. If the requested data size exceeds 512KB, it will cause the time out calculation to overflow since transfer length is 32-bit unsigned integer. This issue is resolved by using 64-bit unsigned integer to perform the arithmetic.

Natinst-ReviewBoard-ID 150232

---
 drivers/spi/spi.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

index 51ad42fad567..ac889df9b1f3 100644
@@ -960,7 +960,7 @@ static int spi_transfer_one_message(struct spi_master *master,
 	struct spi_transfer *xfer;
 	bool keep_cs = false;
 	int ret = 0;
-	unsigned long ms = 1;
+	unsigned long long ms = 1;
 	struct spi_statistics *statm = &master->statistics;
 	struct spi_statistics *stats = &msg->spi->statistics;
 

@@ -991,9 +991,13 @@ static int spi_transfer_one_message(struct spi_master *master,
 
 			if (ret > 0) {
 				ret = 0;
-				ms = xfer->len * 8 * 1000 / xfer->speed_hz;
+				ms = 8LL * 1000LL * xfer->len;
+				do_div(ms, xfer->speed_hz);
 				ms += ms + 100; /* some tolerance */
 
+				if (ms > UINT_MAX)
+					ms = UINT_MAX;
+
 				ms = wait_for_completion_timeout(&master->xfer_completion,
 								 msecs_to_jiffies(ms));
 			}

2.9.3