From: Phil Sutter <phil@xxxxxx>
Deletion of the last rule referencing a given idletimer may happen at
the same time as a read of its file in sysfs:
| ======================================================
| WARNING: possible circular locking dependency detected
| 6.12.0-rc7-01692-g5e9a28f41134-dirty #594 Not tainted
| ------------------------------------------------------
| iptables/3303 is trying to acquire lock:
| ffff8881057e04b8 (kn->active#48){++++}-{0:0}, at: __kernfs_remove+0x20
|
| but task is already holding lock:
| ffffffffa0249068 (list_mutex){+.+.}-{3:3}, at: idletimer_tg_destroy_v]
|
| which lock already depends on the new lock.
A simple reproducer is:
| #!/bin/bash
|
| while true; do
| iptables -A INPUT -i foo -j IDLETIMER --timeout 10 --label "testme"
| iptables -D INPUT -i foo -j IDLETIMER --timeout 10 --label "testme"
| done &
| while true; do
| cat /sys/class/xt_idletimer/timers/testme >/dev/null
| done
Avoid this by freeing list_mutex right after deleting the element from
the list, then continuing with the teardown.
Fixes: 0902b469bd25 ("netfilter: xtables: idletimer target implementation")
Signed-off-by: Phil Sutter <phil@xxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
---
net/netfilter/xt_IDLETIMER.c | 52 +++++++++++++++++++-----------------
1 file changed, 28 insertions(+), 24 deletions(-)
diff --git a/net/netfilter/xt_IDLETIMER.c b/net/netfilter/xt_IDLETIMER.c
index 85f017e37cfc..9f54819eb52c 100644
--- a/net/netfilter/xt_IDLETIMER.c
+++ b/net/netfilter/xt_IDLETIMER.c
@@ -407,21 +407,23 @@ static void idletimer_tg_destroy(const struct xt_tgdtor_param *par)
mutex_lock(&list_mutex);
- if (--info->timer->refcnt == 0) {
- pr_debug("deleting timer %s\n", info->label);
-
- list_del(&info->timer->entry);
- timer_shutdown_sync(&info->timer->timer);
- cancel_work_sync(&info->timer->work);
- sysfs_remove_file(idletimer_tg_kobj, &info->timer->attr.attr);
- kfree(info->timer->attr.attr.name);
- kfree(info->timer);
- } else {
+ if (--info->timer->refcnt > 0) {
pr_debug("decreased refcnt of timer %s to %u\n",
info->label, info->timer->refcnt);
+ mutex_unlock(&list_mutex);
+ return;
}
+ pr_debug("deleting timer %s\n", info->label);
+
+ list_del(&info->timer->entry);
mutex_unlock(&list_mutex);
+
+ timer_shutdown_sync(&info->timer->timer);
+ cancel_work_sync(&info->timer->work);
+ sysfs_remove_file(idletimer_tg_kobj, &info->timer->attr.attr);
+ kfree(info->timer->attr.attr.name);
+ kfree(info->timer);
}
static void idletimer_tg_destroy_v1(const struct xt_tgdtor_param *par)
@@ -432,25 +434,27 @@ static void idletimer_tg_destroy_v1(const struct xt_tgdtor_param *par)
mutex_lock(&list_mutex);
- if (--info->timer->refcnt == 0) {
- pr_debug("deleting timer %s\n", info->label);
-
- list_del(&info->timer->entry);
- if (info->timer->timer_type & XT_IDLETIMER_ALARM) {
- alarm_cancel(&info->timer->alarm);
- } else {
- timer_shutdown_sync(&info->timer->timer);
- }
- cancel_work_sync(&info->timer->work);
- sysfs_remove_file(idletimer_tg_kobj, &info->timer->attr.attr);
- kfree(info->timer->attr.attr.name);
- kfree(info->timer);
- } else {
+ if (--info->timer->refcnt > 0) {
pr_debug("decreased refcnt of timer %s to %u\n",
info->label, info->timer->refcnt);
+ mutex_unlock(&list_mutex);
+ return;
}
+ pr_debug("deleting timer %s\n", info->label);
+
+ list_del(&info->timer->entry);
mutex_unlock(&list_mutex);
+
+ if (info->timer->timer_type & XT_IDLETIMER_ALARM) {
+ alarm_cancel(&info->timer->alarm);
+ } else {
+ timer_shutdown_sync(&info->timer->timer);
+ }
+ cancel_work_sync(&info->timer->work);
+ sysfs_remove_file(idletimer_tg_kobj, &info->timer->attr.attr);
+ kfree(info->timer->attr.attr.name);
+ kfree(info->timer);
}
--
2.30.2
