[PATCH net-next v3 3/5] netconsole: allow configuring the rate limit interval through configfs

[Breno Leitao <leitao@debian.org>]

The per-target token bucket has no interface, so every target is still
unlimited.

Expose the interval as ratelimit_interval_ms through configfs. It
defaults to zero, so a target stays unlimited until an administrator
sets one.

The write restarts the interval instead of only publishing the new
value. A target is configured while it floods, by which point the
bucket is empty, and ___ratelimit() only refills it once the interval
it was set with has elapsed.

Reject more than INT_MAX milliseconds. msecs_to_jiffies() saturates at
MAX_JIFFY_OFFSET, which is below INT_MAX on 32-bit, so checking only
the jiffies value would take a write there that a 64-bit kernel turns
down.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 drivers/net/netconsole.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index c1c92413c0a5c5..d4e3ac272e9b4a 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -958,6 +958,14 @@ static ssize_t transmit_errors_show(struct config_item *item, char *buf)
 	return sysfs_emit(buf, "%llu\n", xmit_drop_count + enomem_count);
 }
 
+static ssize_t ratelimit_interval_ms_show(struct config_item *item, char *buf)
+{
+	struct netconsole_target *nt = to_target(item);
+
+	return sysfs_emit(buf, "%u\n",
+			  jiffies_to_msecs(READ_ONCE(nt->ratelimit.interval)));
+}
+
 /* configfs helper to display if cpu_nr sysdata feature is enabled */
 static ssize_t sysdata_cpu_nr_enabled_show(struct config_item *item, char *buf)
 {
@@ -1353,6 +1361,35 @@ static ssize_t remote_mac_store(struct config_item *item, const char *buf,
 	return ret;
 }
 
+static ssize_t ratelimit_interval_ms_store(struct config_item *item,
+					   const char *buf, size_t count)
+{
+	struct netconsole_target *nt = to_target(item);
+	unsigned int interval;
+	unsigned long jifs;
+	ssize_t ret;
+
+	ret = kstrtouint(buf, 10, &interval);
+	if (ret)
+		return ret;
+
+	/* msecs_to_jiffies() saturates below INT_MAX on 32-bit, so the
+	 * jiffies value alone does not bound what userspace wrote.
+	 */
+	jifs = msecs_to_jiffies(interval);
+	if (interval > INT_MAX || jifs > INT_MAX)
+		return -ERANGE;
+
+	/* Restart the interval, so a target that is already flooding picks
+	 * the new limit up now rather than at the next refill.
+	 */
+	dynamic_netconsole_mutex_lock();
+	ratelimit_state_reset_interval(&nt->ratelimit, jifs);
+	dynamic_netconsole_mutex_unlock();
+
+	return count;
+}
+
 struct userdatum {
 	struct config_item item;
 	char value[MAX_EXTRADATA_VALUE_LEN];
@@ -1717,6 +1754,7 @@ CONFIGFS_ATTR_RO(, local_mac);
 CONFIGFS_ATTR(, remote_mac);
 CONFIGFS_ATTR(, release);
 CONFIGFS_ATTR_RO(, transmit_errors);
+CONFIGFS_ATTR(, ratelimit_interval_ms);
 
 static struct configfs_attribute *netconsole_target_attrs[] = {
 	&attr_enabled,
@@ -1730,6 +1768,7 @@ static struct configfs_attribute *netconsole_target_attrs[] = {
 	&attr_local_mac,
 	&attr_remote_mac,
 	&attr_transmit_errors,
+	&attr_ratelimit_interval_ms,
 	NULL,
 };
 

-- 
2.53.0-Meta