[PATCH 5.15 858/913] ACPI: CPPC: Avoid out of bounds access when parsing _CPC data

[Greg Kroah-Hartman]

From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

commit 40d8abf364bcab23bc715a9221a3c8623956257b upstream.

If the NumEntries field in the _CPC return package is less than 2, do
not attempt to access the "Revision" element of that package, because
it may not be present then.

Fixes: 337aadff8e45 ("ACPI: Introduce CPU performance controls using CPPC")
BugLink: https://lore.kernel.org/lkml/20220322143534.GC32582@xsang-OptiPlex-9020/
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Reviewed-by: Huang Rui <ray.huang@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/acpi/cppc_acpi.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -703,6 +703,11 @@ int acpi_cppc_processor_probe(struct acp
 	cpc_obj = &out_obj->package.elements[0];
 	if (cpc_obj->type == ACPI_TYPE_INTEGER)	{
 		num_ent = cpc_obj->integer.value;
+		if (num_ent <= 1) {
+			pr_debug("Unexpected _CPC NumEntries value (%d) for CPU:%d\n",
+				 num_ent, pr->id);
+			goto out_free;
+		}
 	} else {
 		pr_debug("Unexpected entry type(%d) for NumEntries\n",
 				cpc_obj->type);