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

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Date:   Fri, 28 Jul 2017 15:15:49 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Vinod Koul <vinod.koul@...el.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] dmaengine: rcar-dmac: avoid array overflow

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@...db.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