linux-kernel - Re: Possible null pointer dereference in rcar-dmac.ko

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Date:   Thu, 10 Aug 2017 02:09:21 +0000
From:   Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
To:     Vinod Koul <vinod.koul@...el.com>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>,
        Laurent <laurent.pinchart@...asonboard.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Linux-Kernel <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Anton Volkov <avolkov@...ras.ru>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        ldv-project@...uxtesting.org, dmaengine@...r.kernel.org,
        geert+renesas@...der.be
Subject: Re: Possible null pointer dereference in rcar-dmac.ko

Anton Volkov noticed that engine->dev is NULL before
of_dma_controller_register() in probe.
Thus there might be a NULL pointer dereference in
rcar_dmac_chan_start_xfer while accessing chan->chan.device->dev which
is equal to (&dmac->engine)->dev.
To be more safety code, this patch initialize dmac->engine before it.

Reported-by: Anton Volkov <avolkov@...ras.ru>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
---
> Anton, Laurent

I created this patch because noone posted it yesterday.
Anton, you can use this patch and replace Author to you if you want.
Thus, I used [RFC] on this patch

 drivers/dma/sh/rcar-dmac.c | 51 +++++++++++++++++++++++-----------------------
 1 file changed, 26 insertions(+), 25 deletions(-)

diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
index ffcadca..6d60628 100644
--- a/drivers/dma/sh/rcar-dmac.c
+++ b/drivers/dma/sh/rcar-dmac.c
@@ -1818,8 +1818,32 @@ static int rcar_dmac_probe(struct platform_device *pdev)
 		goto error;
 	}
 
-	/* Initialize the channels. */
-	INIT_LIST_HEAD(&dmac->engine.channels);
+	/* Initialize engine */
+	engine = &dmac->engine;
+
+	dma_cap_set(DMA_MEMCPY, engine->cap_mask);
+	dma_cap_set(DMA_SLAVE, engine->cap_mask);
+
+	engine->dev		= &pdev->dev;
+	engine->copy_align	= ilog2(RCAR_DMAC_MEMCPY_XFER_SIZE);
+
+	engine->src_addr_widths	= widths;
+	engine->dst_addr_widths	= widths;
+	engine->directions	= BIT(DMA_MEM_TO_DEV) | BIT(DMA_DEV_TO_MEM);
+	engine->residue_granularity = DMA_RESIDUE_GRANULARITY_BURST;
+
+	engine->device_alloc_chan_resources	= rcar_dmac_alloc_chan_resources;
+	engine->device_free_chan_resources	= rcar_dmac_free_chan_resources;
+	engine->device_prep_dma_memcpy		= rcar_dmac_prep_dma_memcpy;
+	engine->device_prep_slave_sg		= rcar_dmac_prep_slave_sg;
+	engine->device_prep_dma_cyclic		= rcar_dmac_prep_dma_cyclic;
+	engine->device_config			= rcar_dmac_device_config;
+	engine->device_terminate_all		= rcar_dmac_chan_terminate_all;
+	engine->device_tx_status		= rcar_dmac_tx_status;
+	engine->device_issue_pending		= rcar_dmac_issue_pending;
+	engine->device_synchronize		= rcar_dmac_device_synchronize;
+
+	INIT_LIST_HEAD(&engine->channels);
 
 	for (i = 0; i < dmac->n_channels; ++i) {
 		ret = rcar_dmac_chan_probe(dmac, &dmac->channels[i],
@@ -1839,29 +1863,6 @@ static int rcar_dmac_probe(struct platform_device *pdev)
 	 *
 	 * Default transfer size of 32 bytes requires 32-byte alignment.
 	 */
-	engine = &dmac->engine;
-	dma_cap_set(DMA_MEMCPY, engine->cap_mask);
-	dma_cap_set(DMA_SLAVE, engine->cap_mask);
-
-	engine->dev = &pdev->dev;
-	engine->copy_align = ilog2(RCAR_DMAC_MEMCPY_XFER_SIZE);
-
-	engine->src_addr_widths = widths;
-	engine->dst_addr_widths = widths;
-	engine->directions = BIT(DMA_MEM_TO_DEV) | BIT(DMA_DEV_TO_MEM);
-	engine->residue_granularity = DMA_RESIDUE_GRANULARITY_BURST;
-
-	engine->device_alloc_chan_resources = rcar_dmac_alloc_chan_resources;
-	engine->device_free_chan_resources = rcar_dmac_free_chan_resources;
-	engine->device_prep_dma_memcpy = rcar_dmac_prep_dma_memcpy;
-	engine->device_prep_slave_sg = rcar_dmac_prep_slave_sg;
-	engine->device_prep_dma_cyclic = rcar_dmac_prep_dma_cyclic;
-	engine->device_config = rcar_dmac_device_config;
-	engine->device_terminate_all = rcar_dmac_chan_terminate_all;
-	engine->device_tx_status = rcar_dmac_tx_status;
-	engine->device_issue_pending = rcar_dmac_issue_pending;
-	engine->device_synchronize = rcar_dmac_device_synchronize;
-
 	ret = dma_async_device_register(engine);
 	if (ret < 0)
 		goto error;
-- 
1.9.1