[PATCH 1/2] spi: Fix DMA mapping ownership on partial map failure

If RX mapping fails after TX mapping succeeds, __spi_map_msg() unmaps
TX but leaves tx_sg_mapped set.  If TX mapping fails on a later
transfer, mappings created for earlier transfers remain active.

In both cases, cur_{tx,rx}_dma_dev have not yet been updated because they
are assigned only after every transfer has been mapped.  The subsequent
spi_unmap_msg() may therefore unmap the TX mapping again or release
earlier mappings using a NULL or stale device.  An empty SG table does
not prevent the NULL dereference because dma_unmap_sg_attrs() accesses
the device before checking the entry count.

Publish both mapping devices before mapping starts and unwind all
failures through __spi_unmap_msg().  This clears the mapping flags and
releases each mapping once with the device that created it.

Link: https://lore.kernel.org/r/[email protected]
Fixes: e289df82344f ("spi: Rework per message DMA mapped flag to be per transfer")
Cc: [email protected]
Signed-off-by: Honghui Jiang <[email protected]>
---
 drivers/spi/spi.c | 33 ++++++++++++++++++---------------
 1 file changed, 18 insertions(+), 15 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index d9e6b4b87..05a852494 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1231,6 +1231,8 @@ void spi_unmap_buf(struct spi_controller *ctlr, struct device *dev,
 	spi_unmap_buf_attrs(ctlr, dev, sgt, dir, 0);
 }
 
+static int __spi_unmap_msg(struct spi_controller *ctlr, struct spi_message *msg);
+
 static int __spi_map_msg(struct spi_controller *ctlr, struct spi_message *msg)
 {
 	struct device *tx_dev, *rx_dev;
@@ -1254,7 +1256,14 @@ static int __spi_map_msg(struct spi_controller *ctlr, struct spi_message *msg)
 	else
 		rx_dev = ctlr->dev.parent;
 
-	ret = -ENOMSG;
+	/*
+	 * Store the devices before mapping so partial failures can be unwound
+	 * with the device that created each mapping.
+	 */
+	ctlr->cur_tx_dma_dev = tx_dev;
+	ctlr->cur_rx_dma_dev = rx_dev;
+
+	ret = 0;
 	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
 		/* The sync is done before each transfer. */
 		unsigned long attrs = DMA_ATTR_SKIP_CPU_SYNC;
@@ -1268,7 +1277,7 @@ static int __spi_map_msg(struct spi_controller *ctlr, struct spi_message *msg)
 						xfer->len, DMA_TO_DEVICE,
 						attrs);
 			if (ret != 0)
-				return ret;
+				goto unwind;
 
 			xfer->tx_sg_mapped = true;
 		}
@@ -1277,25 +1286,19 @@ static int __spi_map_msg(struct spi_controller *ctlr, struct spi_message *msg)
 			ret = spi_map_buf_attrs(ctlr, rx_dev, &xfer->rx_sg,
 						xfer->rx_buf, xfer->len,
 						DMA_FROM_DEVICE, attrs);
-			if (ret != 0) {
-				spi_unmap_buf_attrs(ctlr, tx_dev,
-						&xfer->tx_sg, DMA_TO_DEVICE,
-						attrs);
-
-				return ret;
-			}
+			if (ret != 0)
+				goto unwind;
 
 			xfer->rx_sg_mapped = true;
 		}
 	}
-	/* No transfer has been mapped, bail out with success */
-	if (ret)
-		return 0;
-
-	ctlr->cur_rx_dma_dev = rx_dev;
-	ctlr->cur_tx_dma_dev = tx_dev;
 
 	return 0;
+
+unwind:
+	__spi_unmap_msg(ctlr, msg);
+
+	return ret;
 }
 
 static int __spi_unmap_msg(struct spi_controller *ctlr, struct spi_message *msg)
-- 
2.43.0