[PATCH] spi: Fix erroneous sgs value with min_t()

[PATCH] spi: Fix erroneous sgs value with min_t()

[Biju Das]

While computing sgs in spi_map_buf(), the data type
used in min_t() for max_seg_size is 'unsigned int' where
as that of ctlr->max_dma_len is 'size_t'.

min_t(unsigned int,x,y) gives wrong results if one of x/y is
'size_t'

Consider the below examples on a 64-bit machine (ie size_t is
64-bits, and unsigned int is 32-bit).
    case 1) min_t(unsigned int, 5, 0x100000001);
    case 2) min_t(size_t, 5, 0x100000001);

Case 1 returns '1', where as case 2 returns '5'. As you can see
the result from case 1 is wrong.

This patch fixes the above issue by using the data type of the
parameters that are used in min_t with maximum data length.

Fixes: commit 1a4e53d2fc4f68aa ("spi: Fix invalid sgs value")
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
---
 drivers/spi/spi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index d96082dc3340..fb2896cdb3ce 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1019,10 +1019,10 @@ int spi_map_buf(struct spi_controller *ctlr, struct device *dev,
 	int i, ret;
 
 	if (vmalloced_buf || kmap_buf) {
-		desc_len = min_t(unsigned int, max_seg_size, PAGE_SIZE);
+		desc_len = min_t(unsigned long, max_seg_size, PAGE_SIZE);
 		sgs = DIV_ROUND_UP(len + offset_in_page(buf), desc_len);
 	} else if (virt_addr_valid(buf)) {
-		desc_len = min_t(unsigned int, max_seg_size, ctlr->max_dma_len);
+		desc_len = min_t(size_t, max_seg_size, ctlr->max_dma_len);
 		sgs = DIV_ROUND_UP(len, desc_len);
 	} else {
 		return -EINVAL;
-- 
2.17.1

Re: [PATCH] spi: Fix erroneous sgs value with min_t()

[Mark Brown]

On Wed, 16 Mar 2022 17:53:17 +0000, Biju Das wrote:
> While computing sgs in spi_map_buf(), the data type
> used in min_t() for max_seg_size is 'unsigned int' where
> as that of ctlr->max_dma_len is 'size_t'.
> 
> min_t(unsigned int,x,y) gives wrong results if one of x/y is
> 'size_t'
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next

Thanks!

[1/1] spi: Fix erroneous sgs value with min_t()
      commit: ebc4cb43ea5ada3db46c80156fca58a54b9bbca8

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