[PATCH 4.1 002/123] cxl: Check if afu is not null in cxl_slbia

[Greg Kroah-Hartman]

4.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Axtens <dja@xxxxxxxxxx>

commit 2c069a118fe1d80c47dca84e1561045fc7f3cc9e upstream.

The pointer to an AFU in the adapter's list of AFUs can be null
if we're in the process of removing AFUs. The afu_list_lock
doesn't guard against this.

Say we have 2 slices, and we're in the process of removing cxl.
 - We remove the AFUs in order (see cxl_remove). In cxl_remove_afu
   for AFU 0, we take the lock, set adapter->afu[0] = NULL, and
   release the lock.
 - Then we get an slbia. In cxl_slbia we take the lock, and set
   afu = adapter->afu[0], which is NULL.
 - Therefore our attempt to check afu->enabled will blow up.

Therefore, check if afu is a null pointer before dereferencing it.

Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx>
Acked-by: Michael Neuling <mikey@xxxxxxxxxxx>
Acked-by: Ian Munsie <imunsie@xxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/misc/cxl/main.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/misc/cxl/main.c
+++ b/drivers/misc/cxl/main.c
@@ -73,7 +73,7 @@ static inline void cxl_slbia_core(struct
 		spin_lock(&adapter->afu_list_lock);
 		for (slice = 0; slice < adapter->slices; slice++) {
 			afu = adapter->afu[slice];
-			if (!afu->enabled)
+			if (!afu || !afu->enabled)
 				continue;
 			rcu_read_lock();
 			idr_for_each_entry(&afu->contexts_idr, ctx, id)


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