[PATCH v2] genirq: procfs: Make smp_affinity read-only for interrupts that userspace can't set

[Jeff Xie <jeff.xie@linux.dev>]

The kernel already knows at the time of interrupt allocation that the
affinity cannot be controlled by userspace and therefore creating the
file with write permissions is wrong.

Therefore set the file permissions to read-only for such interrupts.

Signed-off-by: Jeff Xie <jeff.xie@linux.dev>
---
v2:
- Updated the description suggested by tglx
- Corrected the return value from -EIO to -EPERM when the userspace can't set the affinity

 kernel/irq/proc.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index 8cccdf40725a..7b3a4c92d148 100644
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -142,7 +142,7 @@ static ssize_t write_irq_affinity(int type, struct file *file,
 	int err;
 
 	if (!irq_can_set_affinity_usr(irq) || no_irq_affinity)
-		return -EIO;
+		return -EPERM;
 
 	if (!zalloc_cpumask_var(&new_value, GFP_KERNEL))
 		return -ENOMEM;
@@ -340,6 +340,7 @@ void register_irq_proc(unsigned int irq, struct irq_desc *desc)
 	static DEFINE_MUTEX(register_lock);
 	void __maybe_unused *irqp = (void *)(unsigned long) irq;
 	char name [MAX_NAMELEN];
+	umode_t umode = S_IRUGO;
 
 	if (!root_irq_dir || (desc->irq_data.chip == &no_irq_chip))
 		return;
@@ -362,8 +363,11 @@ void register_irq_proc(unsigned int irq, struct irq_desc *desc)
 		goto out_unlock;
 
 #ifdef CONFIG_SMP
+	if (irq_can_set_affinity_usr(desc->irq_data.irq))
+		umode |= S_IWUSR;
+
 	/* create /proc/irq/<irq>/smp_affinity */
-	proc_create_data("smp_affinity", 0644, desc->dir,
+	proc_create_data("smp_affinity", umode, desc->dir,
 			 &irq_affinity_proc_ops, irqp);
 
 	/* create /proc/irq/<irq>/affinity_hint */
@@ -371,7 +375,7 @@ void register_irq_proc(unsigned int irq, struct irq_desc *desc)
 			irq_affinity_hint_proc_show, irqp);
 
 	/* create /proc/irq/<irq>/smp_affinity_list */
-	proc_create_data("smp_affinity_list", 0644, desc->dir,
+	proc_create_data("smp_affinity_list", umode, desc->dir,
 			 &irq_affinity_list_proc_ops, irqp);
 
 	proc_create_single_data("node", 0444, desc->dir, irq_node_proc_show,
-- 
2.34.1