netdev - [RFC PATCH 2/4] b44: Fix off-by-one error in acceptable address range

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Message-Id: <201912080836.xB88amHd015549@sdf.org>
Date:   Sun, 8 Dec 2019 08:36:48 GMT
From:   George Spelvin <lkml@....org>
To:     michael.chan@...adcom.com, netdev@...r.kernel.org
Cc:     hauke@...ke-m.de, lkml@....org
Subject: [RFC PATCH 2/4] b44: Fix off-by-one error in acceptable address range

The requirement is dma_addr + size <= 0x40000000, not 0x3fffffff.

In a logically separate but overlapping change, this patch also
rearranges the logic for detecting failures to use a goto rather
than testing dma_mapping_error() twice.  The latter is expensive if
CONFIG_DMA_API_DEBUG is set, but also for bug-proofing reasons I try to
avoid having the same condition in two places that must be kept in sync.

Signed-off-by: George Spelvin <lkml@....org>
---
 drivers/net/ethernet/broadcom/b44.c | 42 ++++++++++++++++-------------
 1 file changed, 24 insertions(+), 18 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/b44.c b/drivers/net/ethernet/broadcom/b44.c
index 394671230c1c..e540d5646aef 100644
--- a/drivers/net/ethernet/broadcom/b44.c
+++ b/drivers/net/ethernet/broadcom/b44.c
@@ -680,12 +680,13 @@ static int b44_alloc_rx_skb(struct b44 *bp, int src_idx, u32 dest_idx_unmasked)
 
 	/* Hardware bug work-around, the chip is unable to do PCI DMA
 	   to/from anything above 1GB :-( */
-	if (dma_mapping_error(bp->sdev->dma_dev, mapping) ||
-		mapping + RX_PKT_BUF_SZ > DMA_BIT_MASK(30)) {
+	if (dma_mapping_error(bp->sdev->dma_dev, mapping))
+		goto workaround;
+	if (mapping + RX_PKT_BUF_SZ > DMA_BIT_MASK(30)+1) {
 		/* Sigh... */
-		if (!dma_mapping_error(bp->sdev->dma_dev, mapping))
-			dma_unmap_single(bp->sdev->dma_dev, mapping,
-					     RX_PKT_BUF_SZ, DMA_FROM_DEVICE);
+		dma_unmap_single(bp->sdev->dma_dev, mapping,
+				 RX_PKT_BUF_SZ, DMA_FROM_DEVICE);
+workaround:
 		dev_kfree_skb_any(skb);
 		skb = alloc_skb(RX_PKT_BUF_SZ, GFP_ATOMIC | GFP_DMA);
 		if (skb == NULL)
@@ -693,10 +694,12 @@ static int b44_alloc_rx_skb(struct b44 *bp, int src_idx, u32 dest_idx_unmasked)
 		mapping = dma_map_single(bp->sdev->dma_dev, skb->data,
 					 RX_PKT_BUF_SZ,
 					 DMA_FROM_DEVICE);
-		if (dma_mapping_error(bp->sdev->dma_dev, mapping) ||
-		    mapping + RX_PKT_BUF_SZ > DMA_BIT_MASK(30)) {
-			if (!dma_mapping_error(bp->sdev->dma_dev, mapping))
-				dma_unmap_single(bp->sdev->dma_dev, mapping, RX_PKT_BUF_SZ,DMA_FROM_DEVICE);
+		if (dma_mapping_error(bp->sdev->dma_dev, mapping))
+			goto failed;
+		if (mapping + RX_PKT_BUF_SZ > DMA_BIT_MASK(30)+1) {
+			dma_unmap_single(bp->sdev->dma_dev, mapping,
+					 RX_PKT_BUF_SZ, DMA_FROM_DEVICE);
+failed:
 			dev_kfree_skb_any(skb);
 			return -ENOMEM;
 		}
@@ -990,24 +993,27 @@ static netdev_tx_t b44_start_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	mapping = dma_map_single_attrs(bp->sdev->dma_dev, skb->data, len,
 				       DMA_TO_DEVICE, DMA_ATTR_NO_WARN);
-	if (dma_mapping_error(bp->sdev->dma_dev, mapping) || mapping + len > DMA_BIT_MASK(30)) {
+	if (dma_mapping_error(bp->sdev->dma_dev, mapping))
+	       goto workaround;
+	if (mapping + len > DMA_BIT_MASK(30)+1) {
 		struct sk_buff *bounce_skb;
 
 		/* Chip can't handle DMA to/from >1GB, use bounce buffer */
-		if (!dma_mapping_error(bp->sdev->dma_dev, mapping))
-			dma_unmap_single(bp->sdev->dma_dev, mapping, len,
-					     DMA_TO_DEVICE);
-
+		dma_unmap_single(bp->sdev->dma_dev, mapping, len,
+				 DMA_TO_DEVICE);
+workaround:
 		bounce_skb = alloc_skb(len, GFP_ATOMIC | GFP_DMA);
 		if (!bounce_skb)
 			goto err_out;
 
 		mapping = dma_map_single(bp->sdev->dma_dev, bounce_skb->data,
 					 len, DMA_TO_DEVICE);
-		if (dma_mapping_error(bp->sdev->dma_dev, mapping) || mapping + len > DMA_BIT_MASK(30)) {
-			if (!dma_mapping_error(bp->sdev->dma_dev, mapping))
-				dma_unmap_single(bp->sdev->dma_dev, mapping,
-						     len, DMA_TO_DEVICE);
+		if (dma_mapping_error(bp->sdev->dma_dev, mapping))
+		       goto failed;
+		if (mapping + len > DMA_BIT_MASK(30)+1) {
+			dma_unmap_single(bp->sdev->dma_dev, mapping, len,
+					 DMA_TO_DEVICE);
+failed:
 			dev_kfree_skb_any(bounce_skb);
 			goto err_out;
 		}
-- 
2.24.0