2024-03-31 05:37:04

by Dawei Li

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 <[email protected]>
---
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

2024-04-02 12:44:13

by Alexandra Winter

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

On 31.03.24 07:34, Dawei Li wrote:
> 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]>
> ---

LGTM;
Thank you Eric for the comment and solution with the 'static' keyword.
Reviewed-by: Alexandra Winter <[email protected]>