net/iucv: Avoid explicit cpumask var allocation on stack

jira VULN-44434
jira VULN-44433
cve CVE-2024-42094
commit-author Dawei Li <[email protected]>
commit be4e130

For CONFIG_CPUMASK_OFFSTACK=y kernel, explicit allocation of cpumask
variable on stack is not recommended since it can cause potential stack
overflow.

Instead, kernel code should always use *cpumask_var API(s) to allocate
cpumask var in config-neutral way, leaving allocation strategy to
CONFIG_CPUMASK_OFFSTACK.

Use *cpumask_var API(s) to address it.

	Signed-off-by: Dawei Li <[email protected]>
	Reviewed-by: Alexandra Winter <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
	Signed-off-by: Jakub Kicinski <[email protected]>
(cherry picked from commit be4e130)
	Signed-off-by: Jonathan Maple <[email protected]>

Author: PlaidCat

net/iucv/iucv.c

@@ -578,7 +578,7 @@ static void iucv_setmask_mp(void)
  */
 static void iucv_setmask_up(void)
 {
-	cpumask_t cpumask;
+	static cpumask_t cpumask;
 	int cpu;
 
 	/* Disable all cpu but the first in cpu_irq_cpumask. */
@@ -686,23 +686,33 @@ static int iucv_cpu_online(unsigned int cpu)
 
 static int iucv_cpu_down_prep(unsigned int cpu)
 {
-	cpumask_t cpumask;
+	cpumask_var_t cpumask;
+	int ret = 0;
 
 	if (!iucv_path_table)
 		return 0;
 
-	cpumask_copy(&cpumask, &iucv_buffer_cpumask);
-	cpumask_clear_cpu(cpu, &cpumask);
-	if (cpumask_empty(&cpumask))
+	if (!alloc_cpumask_var(&cpumask, GFP_KERNEL))
+		return -ENOMEM;
+
+	cpumask_copy(cpumask, &iucv_buffer_cpumask);
+	cpumask_clear_cpu(cpu, cpumask);
+	if (cpumask_empty(cpumask)) {
 		/* Can't offline last IUCV enabled cpu. */
-		return -EINVAL;
+		ret = -EINVAL;
+		goto __free_cpumask;
+	}
 
 	iucv_retrieve_cpu(NULL);
 	if (!cpumask_empty(&iucv_irq_cpumask))
-		return 0;
+		goto __free_cpumask;
+
 	smp_call_function_single(cpumask_first(&iucv_buffer_cpumask),
 				 iucv_allow_cpu, NULL, 1);
-	return 0;
+
+__free_cpumask:
+	free_cpumask_var(cpumask);
+	return ret;
 }
 
 /**