The following commit has been merged in the base/net-next branch: commit abac3ac97fe8734b620e7322a116450d7f90aa43 Author: Vladislav Efanov VEfanov@ispras.ru Date: Fri May 26 19:16:32 2023 +0300

batman-adv: Broken sync while rescheduling delayed work

Syzkaller got a lot of crashes like: KASAN: use-after-free Write in *_timers*

All of these crashes point to the same memory area:

The buggy address belongs to the object at ffff88801f870000 which belongs to the cache kmalloc-8k of size 8192 The buggy address is located 5320 bytes inside of 8192-byte region [ffff88801f870000, ffff88801f872000)

This area belongs to : batadv_priv->batadv_priv_dat->delayed_work->timer_list

The reason for these issues is the lack of synchronization. Delayed work (batadv_dat_purge) schedules new timer/work while the device is being deleted. As the result new timer/delayed work is set after cancel_delayed_work_sync() was called. So after the device is freed the timer list contains pointer to already freed memory.

Found by Linux Verification Center (linuxtesting.org) with syzkaller.

Cc: stable@kernel.org Fixes: 2f1dfbe18507 ("batman-adv: Distributed ARP Table - implement local storage") Signed-off-by: Vladislav Efanov VEfanov@ispras.ru Acked-by: Sven Eckelmann sven@narfation.org Signed-off-by: Simon Wunderlich sw@simonwunderlich.de

diff --git a/net/batman-adv/distributed-arp-table.c b/net/batman-adv/distributed-arp-table.c index 6968e55eb971..28a939d56090 100644 --- a/net/batman-adv/distributed-arp-table.c +++ b/net/batman-adv/distributed-arp-table.c @@ -101,7 +101,6 @@ static void batadv_dat_purge(struct work_struct *work); */ static void batadv_dat_start_timer(struct batadv_priv *bat_priv) { - INIT_DELAYED_WORK(&bat_priv->dat.work, batadv_dat_purge); queue_delayed_work(batadv_event_workqueue, &bat_priv->dat.work, msecs_to_jiffies(10000)); } @@ -819,6 +818,7 @@ int batadv_dat_init(struct batadv_priv *bat_priv) if (!bat_priv->dat.hash) return -ENOMEM;

+ INIT_DELAYED_WORK(&bat_priv->dat.work, batadv_dat_purge); batadv_dat_start_timer(bat_priv);

batadv_tvlv_handler_register(bat_priv, batadv_dat_tvlv_ogm_handler_v1,