linux-kernel - [PATCH net-next v2 1/2] net/iucv: Avoid explicit cpumask var allocation on stack

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Message-Id: <20240331053441.1276826-2-dawei.li@shingroup.cn>
Date: Sun, 31 Mar 2024 13:34:40 +0800
From: Dawei Li <dawei.li@...ngroup.cn>
To: davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	ioana.ciornei@....com,
	wintera@...ux.ibm.com,
	twinkler@...ux.ibm.com
Cc: netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-s390@...r.kernel.org,
	Dawei Li <dawei.li@...ngroup.cn>
Subject: [PATCH net-next v2 1/2] net/iucv: Avoid explicit cpumask var allocation on stack

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@...ngroup.cn>
---
 net/iucv/iucv.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/net/iucv/iucv.c b/net/iucv/iucv.c
index a4ab615ca3e3..5e37a8ceebcb 100644
--- a/net/iucv/iucv.c
+++ b/net/iucv/iucv.c
@@ -520,7 +520,7 @@ 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. */
@@ -628,23 +628,33 @@ 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;
 }
 
 /**
-- 
2.27.0