[PATCH] dmaengine: rcar-dmac: avoid array overflow

[Arnd Bergmann <arnd@arndb.de>]

Building with CONFIG_UBSAN_SANITIZE_ALL shows this warning:

drivers/dma/sh/rcar-dmac.c: In function 'rcar_dmac_chan_prep_sg':
drivers/dma/sh/rcar-dmac.c:839:29: error: array subscript is above array bounds [-Werror=array-bounds]
  desc->chcr = chcr | chcr_ts[desc->xfer_shift];

As the compiler doesn't know what the xfer_size is, it is impossible
to rule out the array overflow here. As we know that xfer_size
can only be within enum dma_slave_buswidth, this will not overflow
for correct users, and adding a range check will handle the
obscure case and shut up the warning.

Fixes: 87244fe5abdf ("dmaengine: rcar-dmac: Add Renesas R-Car Gen2 DMA Controller (DMAC) driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/dma/sh/rcar-dmac.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
index ffcadca53243..f5b28eb4009e 100644
--- a/drivers/dma/sh/rcar-dmac.c
+++ b/drivers/dma/sh/rcar-dmac.c
@@ -836,7 +836,8 @@ static void rcar_dmac_chan_configure_desc(struct rcar_dmac_chan *chan,
 	}
 
 	desc->xfer_shift = ilog2(xfer_size);
-	desc->chcr = chcr | chcr_ts[desc->xfer_shift];
+	if (desc->xfer_shift < ARRAY_SIZE(chcr_ts))
+		desc->chcr = chcr | chcr_ts[desc->xfer_shift];
 }
 
 /*
-- 
2.9.0