of: overlay: fix null pointer dereferencing in find_dup_cset_node_entry() and find_dup_cset_prop()

When kmalloc() fail to allocate memory in kasprintf(), fn_1 or fn_2 will
be NULL, and strcmp() will cause null pointer dereference.

Fixes: 2fe0e876 ("of: overlay: check prevents multiple fragments touching same property")
Signed-off-by: ruanjinjie <ruanjinjie@huawei.com>
Link: https://lore.kernel.org/r/20221211023337.592266-1-ruanjinjie@huawei.comSigned-off-by: Rob Herring <robh@kernel.org>

drivers/of/overlay.c

@@ -545,7 +545,7 @@ static int find_dup_cset_node_entry(struct overlay_changeset *ovcs,
 
 		fn_1 = kasprintf(GFP_KERNEL, "%pOF", ce_1->np);
 		fn_2 = kasprintf(GFP_KERNEL, "%pOF", ce_2->np);
-		node_path_match = !strcmp(fn_1, fn_2);
+		node_path_match = !fn_1 || !fn_2 || !strcmp(fn_1, fn_2);
 		kfree(fn_1);
 		kfree(fn_2);
 		if (node_path_match) {
@@ -580,7 +580,7 @@ static int find_dup_cset_prop(struct overlay_changeset *ovcs,
 
 		fn_1 = kasprintf(GFP_KERNEL, "%pOF", ce_1->np);
 		fn_2 = kasprintf(GFP_KERNEL, "%pOF", ce_2->np);
-		node_path_match = !strcmp(fn_1, fn_2);
+		node_path_match = !fn_1 || !fn_2 || !strcmp(fn_1, fn_2);
 		kfree(fn_1);
 		kfree(fn_2);
 		if (node_path_match &&