Messages in this thread | | | From | Eric Dumazet <> | Date | Thu, 30 Jun 2022 16:44:29 +0200 | Subject | Re: [PATCH net] net: rose: fix UAF bug caused by rose_t0timer_expiry |
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On Thu, Jun 30, 2022 at 4:38 PM Duoming Zhou <duoming@zju.edu.cn> wrote: > > There are UAF bugs caused by rose_t0timer_expiry(). The > root cause is that del_timer() could not stop the timer > handler that is running and there is no synchronization. > One of the race conditions is shown below: > > (thread 1) | (thread 2) > | rose_device_event > | rose_rt_device_down > | rose_remove_neigh > rose_t0timer_expiry | rose_stop_t0timer(rose_neigh) > ... | del_timer(&neigh->t0timer) > | kfree(rose_neigh) //[1]FREE > neigh->dce_mode //[2]USE | > > The rose_neigh is deallocated in position [1] and use in > position [2]. > > The crash trace triggered by POC is like below: > > BUG: KASAN: use-after-free in expire_timers+0x144/0x320 > Write of size 8 at addr ffff888009b19658 by task swapper/0/0 > ... > Call Trace: > <IRQ> > dump_stack_lvl+0xbf/0xee > print_address_description+0x7b/0x440 > print_report+0x101/0x230 > ? expire_timers+0x144/0x320 > kasan_report+0xed/0x120 > ? expire_timers+0x144/0x320 > expire_timers+0x144/0x320 > __run_timers+0x3ff/0x4d0 > run_timer_softirq+0x41/0x80 > __do_softirq+0x233/0x544 > ... > > This patch changes del_timer() in rose_stop_t0timer() and > rose_stop_ftimer() to del_timer_sync() in order that the > timer handler could be finished before the resources such as > rose_neigh and so on are deallocated. As a result, the UAF > bugs could be mitigated. > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Signed-off-by: Duoming Zhou <duoming@zju.edu.cn> > --- > net/rose/rose_link.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/net/rose/rose_link.c b/net/rose/rose_link.c > index 8b96a56d3a4..9734d1264de 100644 > --- a/net/rose/rose_link.c > +++ b/net/rose/rose_link.c > @@ -54,12 +54,12 @@ static void rose_start_t0timer(struct rose_neigh *neigh) > > void rose_stop_ftimer(struct rose_neigh *neigh) > { > - del_timer(&neigh->ftimer); > + del_timer_sync(&neigh->ftimer); > }
Are you sure this is safe ?
del_timer_sync() could hang if the caller holds a lock that the timer function would need to acquire.
> > void rose_stop_t0timer(struct rose_neigh *neigh) > { > - del_timer(&neigh->t0timer); > + del_timer_sync(&neigh->t0timer); > }
Same here, please explain why it is safe.
> > int rose_ftimer_running(struct rose_neigh *neigh) > -- > 2.17.1 >
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