[PATCH v3] IB/hfi1: Fix possible null-pointer dereference in _extend_sdma_tx_descs()

kmalloc_array() is called to allocate memory for tx->descp. If it fails,
the function __sdma_txclean() is called:
  __sdma_txclean(dd, tx);

However, in the function __sdma_txclean(), tx-descp is dereferenced if
tx->num_desc is not zero:
  sdma_unmap_desc(dd, &tx->descp[0]);

To fix this possible null-pointer dereference, assign the return value of
kmalloc_array() to a local variable descp, and then assign it to tx->descp
if it is not NULL. Otherwise, go to enomem.

Fixes: 7724105686e7 ("IB/hfi1: add driver files")
Reported-by: TOTE Robot <redacted>
Signed-off-by: Tuo Li <redacted>
---
v3:
* Add fixes line.
  Thank Jason Gunthorpe for helpful advice.
v2:
* Assign the return value of kmalloc_array() to a local variable and then
check it instead of assigning 0 to tx->num_desc when memory allocation
fails.
  Thank Mike Marciniszyn for helpful advice.
---
 drivers/infiniband/hw/hfi1/sdma.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/infiniband/hw/hfi1/sdma.c b/drivers/infiniband/hw/hfi1/sdma.c
index eb15c310d63d..6ca8d065f44e 100644
--- a/drivers/infiniband/hw/hfi1/sdma.c
+++ b/drivers/infiniband/hw/hfi1/sdma.c

@@ -3055,6 +3055,7 @@ static void __sdma_process_event(struct sdma_engine *sde,
 static int _extend_sdma_tx_descs(struct hfi1_devdata *dd, struct sdma_txreq *tx)
 {
 	int i;
+	struct sdma_desc *descp;
 
 	/* Handle last descriptor */
 	if (unlikely((tx->num_desc == (MAX_DESC - 1)))) {

@@ -3075,12 +3076,12 @@ static int _extend_sdma_tx_descs(struct hfi1_devdata *dd, struct sdma_txreq *tx)
 	if (unlikely(tx->num_desc == MAX_DESC))
 		goto enomem;
 
-	tx->descp = kmalloc_array(
-			MAX_DESC,
-			sizeof(struct sdma_desc),
-			GFP_ATOMIC);
-	if (!tx->descp)
+	descp = kmalloc_array(MAX_DESC,
+					sizeof(struct sdma_desc),
+					GFP_ATOMIC);
+	if (!descp)
 		goto enomem;
+	tx->descp = descp;
 
 	/* reserve last descriptor for coalescing */
 	tx->desc_limit = MAX_DESC - 1;

-- 
2.25.1