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netfilter: IDLETIMER: Fix for possible ABBA deadlock

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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@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Phil Sutter 2024-12-06 19:32:29 +01:00 committed by Pablo Neira Ayuso
parent d92906fd1b
commit f36b01994d
1 changed files with 28 additions and 24 deletions
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52
net/netfilter/xt_IDLETIMER.c
View File

@ -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);
}