[PATCH] mm/vmstat: reject invalid stat_interval values

[Cao Ruichuang]

vm.stat_interval is exposed in seconds, but proc_dointvec_jiffies()
currently accepts zero and negative values. In the current tree,
writing 0 succeeds and leaves /proc/sys/vm/stat_interval at 0.

vmstat_update() uses the stored jiffy interval directly when it
requeues its delayed work, so a zero interval can drive excessive
kworker CPU usage. Negative values are not meaningful either.

Switch vm.stat_interval to a small custom sysctl handler that keeps
the existing seconds-based userspace ABI while rejecting values below
1 and capping the upper bound at INT_MAX / HZ.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=220226
Signed-off-by: Cao Ruichuang <create0818@xxxxxxx>
---
 mm/vmstat.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 86b14b0f77b..f48d3bdad64 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1964,6 +1964,7 @@ static const struct seq_operations vmstat_op = {
 #ifdef CONFIG_SMP
 static DEFINE_PER_CPU(struct delayed_work, vmstat_work);
 static int sysctl_stat_interval __read_mostly = HZ;
+static const int sysctl_stat_interval_max = INT_MAX / HZ;
 static int vmstat_late_init_done;
 
 #ifdef CONFIG_PROC_FS
@@ -1972,6 +1973,26 @@ static void refresh_vm_stats(struct work_struct *work)
 	refresh_cpu_vm_stats(true);
 }
 
+static int vmstat_stat_interval_handler(const struct ctl_table *table, int write,
+					void *buffer, size_t *lenp, loff_t *ppos)
+{
+	int interval = sysctl_stat_interval / HZ;
+	const struct ctl_table tmp = {
+		.data	= &interval,
+		.maxlen	= sizeof(interval),
+		.mode	= table->mode,
+		.extra1	= SYSCTL_ONE,
+		.extra2	= (void *)&sysctl_stat_interval_max,
+	};
+	int ret;
+
+	ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
+	if (!ret && write)
+		sysctl_stat_interval = interval * HZ;
+
+	return ret;
+}
+
 static int vmstat_refresh(const struct ctl_table *table, int write,
 		   void *buffer, size_t *lenp, loff_t *ppos)
 {
@@ -2236,7 +2257,7 @@ static const struct ctl_table vmstat_table[] = {
 		.data		= &sysctl_stat_interval,
 		.maxlen		= sizeof(sysctl_stat_interval),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec_jiffies,
+		.proc_handler	= vmstat_stat_interval_handler,
 	},
 	{
 		.procname	= "stat_refresh",
-- 
2.39.5 (Apple Git-154)