net/iucv: Avoid explicit cpumask var allocation on stack

JIRA: https://issues.redhat.com/browse/RHEL-56533
CVE: CVE-2024-42094
Upstream status: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Tested: by IBM
Build Info: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=64160214
Conflicts: None

net/iucv: Avoid explicit cpumask var allocation on stack
commit be4e130
Author: Dawei Li <dawei.li@shingroup.cn>
Date:   Sun Mar 31 13:34:40 2024 +0800

    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 <dawei.li@shingroup.cn>
    Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>
    Link: https://lore.kernel.org/r/20240331053441.1276826-2-dawei.li@shingroup.cn
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Mete Durlu <mdurlu@redhat.com>

Author: Mete Durlu

net/iucv/iucv.c

@@ -519,7 +519,7 @@ 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. */
@@ -627,23 +627,33 @@ 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;
 }
 
 /**