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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Eugeniu Rosca <erosca@de.adit-jv.com>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Vinod Koul <vkoul@kernel.org>, Sasha Levin <sashal@kernel.org>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Subject: [PATCH 5.2 020/131] dmaengine: rcar-dmac: Reject zero-length slave DMA requests
Date:   Mon,  5 Aug 2019 15:01:47 +0200
Message-Id: <20190805124952.790372437@linuxfoundation.org>
In-Reply-To: <20190805124951.453337465@linuxfoundation.org>
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[ Upstream commit 78efb76ab4dfb8f74f290ae743f34162cd627f19 ]

While the .device_prep_slave_sg() callback rejects empty scatterlists,
it still accepts single-entry scatterlists with a zero-length segment.
These may happen if a driver calls dmaengine_prep_slave_single() with a
zero len parameter.  The corresponding DMA request will never complete,
leading to messages like:

    rcar-dmac e7300000.dma-controller: Channel Address Error happen

and DMA timeouts.

Although requesting a zero-length DMA request is a driver bug, rejecting
it early eases debugging.  Note that the .device_prep_dma_memcpy()
callback already rejects requests to copy zero bytes.

Reported-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Analyzed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/dma/sh/rcar-dmac.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
index 33ab1b607e2b0..54de669c38b84 100644
--- a/drivers/dma/sh/rcar-dmac.c
+++ b/drivers/dma/sh/rcar-dmac.c
@@ -1165,7 +1165,7 @@ rcar_dmac_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
 	struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);
 
 	/* Someone calling slave DMA on a generic channel? */
-	if (rchan->mid_rid < 0 || !sg_len) {
+	if (rchan->mid_rid < 0 || !sg_len || !sg_dma_len(sgl)) {
 		dev_warn(chan->device->dev,
 			 "%s: bad parameter: len=%d, id=%d\n",
 			 __func__, sg_len, rchan->mid_rid);
-- 
2.20.1