linux-kernel - [PATCH 5/8] vop: vringh: Do not crash if no DMA channel

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Date:   Wed, 16 Jan 2019 17:32:50 +0100
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
To:     sudeep.dutt@...el.com, ashutosh.dixit@...el.com,
        gregkh@...uxfoundation.org, arnd@...db.de
Cc:     linux-kernel@...r.kernel.org, Vincent Whitchurch <rabinv@...s.com>
Subject: [PATCH 5/8] vop: vringh: Do not crash if no DMA channel

Fallback gracefully if no DMA channel is provided instead of
dereferencing NULL pointers.

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>
---
 drivers/misc/mic/vop/vop_vringh.c | 32 +++++++++++++++++++------------
 1 file changed, 20 insertions(+), 12 deletions(-)

diff --git a/drivers/misc/mic/vop/vop_vringh.c b/drivers/misc/mic/vop/vop_vringh.c
index ccdfbb652123..18d6ecff1834 100644
--- a/drivers/misc/mic/vop/vop_vringh.c
+++ b/drivers/misc/mic/vop/vop_vringh.c
@@ -531,12 +531,12 @@ static int vop_virtio_copy_to_user(struct vop_vdev *vdev, void __user *ubuf,
 	void __iomem *dbuf = vpdev->hw_ops->ioremap(vpdev, daddr, len);
 	struct vop_vringh *vvr = &vdev->vvr[vr_idx];
 	struct vop_info *vi = dev_get_drvdata(&vpdev->dev);
-	size_t dma_alignment = 1 << vi->dma_ch->device->copy_align;
-	bool x200 = is_dma_copy_aligned(vi->dma_ch->device, 1, 1, 1);
+	size_t dma_alignment;
+	bool x200;
 	size_t dma_offset, partlen;
 	int err;
 
-	if (!VOP_USE_DMA) {
+	if (!VOP_USE_DMA || !vi->dma_ch) {
 		if (copy_to_user(ubuf, (void __force *)dbuf, len)) {
 			err = -EFAULT;
 			dev_err(vop_dev(vdev), "%s %d err %d\n",
@@ -548,6 +548,9 @@ static int vop_virtio_copy_to_user(struct vop_vdev *vdev, void __user *ubuf,
 		goto err;
 	}
 
+	dma_alignment = 1 << vi->dma_ch->device->copy_align;
+	x200 = is_dma_copy_aligned(vi->dma_ch->device, 1, 1, 1);
+
 	dma_offset = daddr - round_down(daddr, dma_alignment);
 	daddr -= dma_offset;
 	len += dma_offset;
@@ -606,18 +609,23 @@ static int vop_virtio_copy_from_user(struct vop_vdev *vdev, void __user *ubuf,
 	void __iomem *dbuf = vpdev->hw_ops->ioremap(vpdev, daddr, len);
 	struct vop_vringh *vvr = &vdev->vvr[vr_idx];
 	struct vop_info *vi = dev_get_drvdata(&vdev->vpdev->dev);
-	size_t dma_alignment = 1 << vi->dma_ch->device->copy_align;
-	bool x200 = is_dma_copy_aligned(vi->dma_ch->device, 1, 1, 1);
+	size_t dma_alignment;
+	bool x200;
 	size_t partlen;
-	bool dma = VOP_USE_DMA;
+	bool dma = VOP_USE_DMA && vi->dma_ch;
 	int err = 0;
 
-	if (daddr & (dma_alignment - 1)) {
-		vdev->tx_dst_unaligned += len;
-		dma = false;
-	} else if (ALIGN(len, dma_alignment) > dlen) {
-		vdev->tx_len_unaligned += len;
-		dma = false;
+	if (dma) {
+		dma_alignment = 1 << vi->dma_ch->device->copy_align;
+		x200 = is_dma_copy_aligned(vi->dma_ch->device, 1, 1, 1);
+
+		if (daddr & (dma_alignment - 1)) {
+			vdev->tx_dst_unaligned += len;
+			dma = false;
+		} else if (ALIGN(len, dma_alignment) > dlen) {
+			vdev->tx_len_unaligned += len;
+			dma = false;
+		}
 	}
 
 	if (!dma)
-- 
2.20.0