[PATCH 5.1 355/371] powerpc/pseries: Fix oops in hotplug memory notifier

[Greg Kroah-Hartman]

From: Nathan Lynch <nathanl@xxxxxxxxxxxxx>

commit 0aa82c482ab2ece530a6f44897b63b274bb43c8e upstream.

During post-migration device tree updates, we can oops in
pseries_update_drconf_memory() if the source device tree has an
ibm,dynamic-memory-v2 property and the destination has a
ibm,dynamic_memory (v1) property. The notifier processes an "update"
for the ibm,dynamic-memory property but it's really an add in this
scenario. So make sure the old property object is there before
dereferencing it.

Fixes: 2b31e3aec1db ("powerpc/drmem: Add support for ibm, dynamic-memory-v2 property")
Cc: stable@xxxxxxxxxxxxxxx # v4.16+
Signed-off-by: Nathan Lynch <nathanl@xxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/powerpc/platforms/pseries/hotplug-memory.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -980,6 +980,9 @@ static int pseries_update_drconf_memory(
 	if (!memblock_size)
 		return -EINVAL;
 
+	if (!pr->old_prop)
+		return 0;
+
 	p = (__be32 *) pr->old_prop->value;
 	if (!p)
 		return -EINVAL;