[PATCH] dma: dw-axi-dmac: fix null dereference when pointer first is null

[Colin King]

From: Colin Ian King <colin.king@xxxxxxxxxxxxx>

In the unlikely event that axi_desc_get returns a null desc in the
very first iteration of the while-loop the error exit path ends
up calling axi_desc_put on a null pointer 'first' and this causes
a null pointer dereference.  Fix this by adding a null check on
pointer 'first' before calling axi_desc_put.

Addresses-Coverity: ("Explicit null dereference")
fixes: 1fe20f1b8454 ("dmaengine: Introduce DW AXI DMAC driver")
Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
---
 drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
index b2ac1d2c5b86..a1ce307c502f 100644
--- a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
+++ b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
@@ -512,7 +512,8 @@ dma_chan_prep_dma_memcpy(struct dma_chan *dchan, dma_addr_t dst_adr,
 	return vchan_tx_prep(&chan->vc, &first->vd, flags);
 
 err_desc_get:
-	axi_desc_put(first);
+	if (first)
+		axi_desc_put(first);
 	return NULL;
 }
 
-- 
2.20.1