[PATCH] spi: core: Validate lenght of the transfers in message

[PATCH] spi: core: Validate lenght of the transfers in message

[Ivan T. Ivanov]

From: "Ivan T. Ivanov" <iivanov-NEYub+7Iv8PQT0dZR+AlfA@public.gmane.org>

SPI transfer lenght should be a power-of-two multiple
of eight bits.

Signed-off-by: Ivan T. Ivanov <iivanov-NEYub+7Iv8PQT0dZR+AlfA@public.gmane.org>
---
 drivers/spi/spi.c |   17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 23756b0..474c0b0 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1619,6 +1619,7 @@ static int __spi_validate(struct spi_device *spi, struct spi_message *message)
 {
 	struct spi_master *master = spi->master;
 	struct spi_transfer *xfer;
+	int w_size, n_words;
 
 	if (list_empty(&message->transfers))
 		return -EINVAL;
@@ -1670,6 +1671,22 @@ static int __spi_validate(struct spi_device *spi, struct spi_message *message)
 				return -EINVAL;
 		}
 
+		/*
+		 * Word size of the SPI transfer should be a power-of-two
+		 * multiple of eight bits,
+		 */
+		if (xfer->bits_per_word <= 8)
+			w_size = 1;
+		else if (xfer->bits_per_word <= 16)
+			w_size = 2;
+		else
+			w_size = 4;
+
+		n_words = xfer->len / w_size;
+		/* No partial transfers accepted */
+		if (!n_words || xfer->len & (w_size - 1))
+			return -EINVAL;
+
 		if (xfer->speed_hz && master->min_speed_hz &&
 		    xfer->speed_hz < master->min_speed_hz)
 			return -EINVAL;
-- 
1.7.9.5

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Re: [PATCH] spi: core: Validate lenght of the transfers in message

[Gerhard Sittig]

On Thu, Feb 13, 2014 at 16:46 +0200, Ivan T. Ivanov wrote:
> 
> From: "Ivan T. Ivanov" <iivanov-NEYub+7Iv8PQT0dZR+AlfA@public.gmane.org>
> 
> SPI transfer lenght should be a power-of-two multiple
> of eight bits.

Are you suggesting that an SPI transfer cannot consist of e.g.
three bytes?  This would be surprising, and certainly would be
rather wrong an assumption.  Am I missing/misunderstanding
something?


virtually yours
Gerhard Sittig
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Re: [PATCH] spi: core: Validate lenght of the transfers in message

[Mark Brown]

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On Thu, Feb 13, 2014 at 10:27:57PM +0100, Gerhard Sittig wrote:
> On Thu, Feb 13, 2014 at 16:46 +0200, Ivan T. Ivanov wrote:

> > SPI transfer lenght should be a power-of-two multiple
> > of eight bits.

> Are you suggesting that an SPI transfer cannot consist of e.g.
> three bytes?  This would be surprising, and certainly would be
> rather wrong an assumption.  Am I missing/misunderstanding
> something?

The check is supposed to be verifying that the transfer is a whole
number of the current SPI word size as I understand it (not actually
looked at the change yet but that's where it came from, factored out of
a driver).

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Re: [PATCH] spi: core: Validate lenght of the transfers in message

[Ivan T. Ivanov]

On Fri, 2014-02-14 at 00:26 +0000, Mark Brown wrote: 
> On Thu, Feb 13, 2014 at 10:27:57PM +0100, Gerhard Sittig wrote:
> > On Thu, Feb 13, 2014 at 16:46 +0200, Ivan T. Ivanov wrote:
> 
> > > SPI transfer lenght should be a power-of-two multiple
> > > of eight bits.
> 
> > Are you suggesting that an SPI transfer cannot consist of e.g.
> > three bytes?  This would be surprising, and certainly would be
> > rather wrong an assumption.  Am I missing/misunderstanding
> > something?
> 
> The check is supposed to be verifying that the transfer is a whole
> number of the current SPI word size as I understand it (not actually
> looked at the change yet but that's where it came from, factored out of
> a driver).

Yes. Comment is not correct. Is this better?

"SPI transfer length should be multiple of SPI word size, where SPI
word size should be power-of-two multiple"

Regards,
Ivan

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Re: [PATCH] spi: core: Validate lenght of the transfers in message

[Mark Brown]

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On Fri, Feb 14, 2014 at 10:16:05AM +0200, Ivan T. Ivanov wrote:

> "SPI transfer length should be multiple of SPI word size, where SPI
> word size should be power-of-two multiple"

Yes, that's clearer though you could in theory have a three byte word
(I'm not sure that anyone would actually do that but it's possible).  I
do have a comment on the code as well.

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Re: [PATCH] spi: core: Validate lenght of the transfers in message

[Mark Brown]

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On Thu, Feb 13, 2014 at 04:46:46PM +0200, Ivan T. Ivanov wrote:

> +		/* No partial transfers accepted */
> +		if (!n_words || xfer->len & (w_size - 1))
> +			return -EINVAL;

Please write this using % rather than the & - it's a lot clearer what
it's checking for, I had to think what the above meant.  Hopefully the
compiler will make it equally fast either way.

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