[PATCH] dma: mv_xor: Fix a possible null-pointer dereference in mv_xor_prep_dma_xor()

[Jia-Ju Bai <baijiaju1990@xxxxxxxxx>]

In mv_xor_prep_dma_xor(), there is an if statement on line 577 to check
whether sw_desc is NULL:
    if (sw_desc)

When sw_desc is NULL, it is used on line 594:
    dev_dbg(..., sw_desc, &sw_desc->async_tx);

Thus, a possible null-pointer dereference may occur.

To fix this bug, sw_desc is checked before being used.

This bug is found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@xxxxxxxxx>
---
 drivers/dma/mv_xor.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/dma/mv_xor.c b/drivers/dma/mv_xor.c
index 0ac8e7b34e12..08c0b2a9eb32 100644
--- a/drivers/dma/mv_xor.c
+++ b/drivers/dma/mv_xor.c
@@ -589,9 +589,11 @@ mv_xor_prep_dma_xor(struct dma_chan *chan, dma_addr_t dest, dma_addr_t *src,
 		}
 	}
 
-	dev_dbg(mv_chan_to_devp(mv_chan),
-		"%s sw_desc %p async_tx %p \n",
-		__func__, sw_desc, &sw_desc->async_tx);
+	if (sw_desc) {
+		dev_dbg(mv_chan_to_devp(mv_chan),
+			"%s sw_desc %p async_tx %p \n",
+			__func__, sw_desc, &sw_desc->async_tx);
+	}
 	return sw_desc ? &sw_desc->async_tx : NULL;
 }
 
-- 
2.17.0