Re: [PATCH] batman-adv: Broken sync while rescheduling delayed work

[Sven Eckelmann]

On Friday, 26 May 2023 18:16:32 CEST Vladislav Efanov wrote:
> 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.
> 
> Fixes: 2f1dfbe18507 ("batman-adv: Distributed ARP Table - implement local storage")
> Signed-off-by: Vladislav Efanov <VEfanov@xxxxxxxxx>
> ---


Acked-by: Sven Eckelmann <sven@xxxxxxxxxxxxx>

Thanks,
	Sven

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