drm/amdgpu: avoid buffer overflow attach in smu_sys_set_pp_table()

It malicious user provides a small pptable through sysfs and then
a bigger pptable, it may cause buffer overflow attack in function
smu_sys_set_pp_table().

Reviewed-by: Lijo Lazar <[e-mail]>
Signed-off-by: Jiang Liu <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>
Cc: [e-mail]

drivers/gpu/drm/amd/pm/swsmu/amdgpu_smu.c

···
 		return -EIO;
 	}
 
-	if (!smu_table->hardcode_pptable) {
+	if (!smu_table->hardcode_pptable || smu_table->power_play_table_size < size) {
+		kfree(smu_table->hardcode_pptable);
 		smu_table->hardcode_pptable = kzalloc(size, GFP_KERNEL);
 		if (!smu_table->hardcode_pptable)
 			return -ENOMEM;