linux-kernel - [PATCH 4.9 073/145] dmaengine: at_hdmac: fix potential NULL pointer dereference in atc_prep_dma

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Date:   Fri, 23 Feb 2018 19:26:19 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Gustavo A. R. Silva" <garsilva@...eddedor.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        Vinod Koul <vinod.koul@...el.com>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.9 073/145] dmaengine: at_hdmac: fix potential NULL pointer dereference in atc_prep_dma_interleaved

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Gustavo A. R. Silva" <garsilva@...eddedor.com>


[ Upstream commit 62a277d43d47e74972de44d33bd3763e31992414 ]

_xt_ is being dereferenced before it is null checked, hence there is a
potential null pointer dereference.

Fix this by moving the pointer dereference after _xt_ has been null
checked.

This issue was detected with the help of Coccinelle.

Fixes: 4483320e241c ("dmaengine: Use Pointer xt after NULL check.")
Signed-off-by: Gustavo A. R. Silva <garsilva@...eddedor.com>
Acked-by: Ludovic Desroches <ludovic.desroches@...rochip.com>
Signed-off-by: Vinod Koul <vinod.koul@...el.com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/dma/at_hdmac.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/dma/at_hdmac.c
+++ b/drivers/dma/at_hdmac.c
@@ -709,7 +709,7 @@ atc_prep_dma_interleaved(struct dma_chan
 			 unsigned long flags)
 {
 	struct at_dma_chan	*atchan = to_at_dma_chan(chan);
-	struct data_chunk	*first = xt->sgl;
+	struct data_chunk	*first;
 	struct at_desc		*desc = NULL;
 	size_t			xfer_count;
 	unsigned int		dwidth;
@@ -721,6 +721,8 @@ atc_prep_dma_interleaved(struct dma_chan
 	if (unlikely(!xt || xt->numf != 1 || !xt->frame_size))
 		return NULL;
 
+	first = xt->sgl;
+
 	dev_info(chan2dev(chan),
 		 "%s: src=%pad, dest=%pad, numf=%d, frame_size=%d, flags=0x%lx\n",
 		__func__, &xt->src_start, &xt->dst_start, xt->numf,