Messages in this thread | | | Date | Thu, 30 Jun 2022 23:51:21 +0800 (GMT+08:00) | From | duoming@zju ... | Subject | Re: [PATCH net] net: rose: fix UAF bug caused by rose_t0timer_expiry |
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Hello,
On Thu, 30 Jun 2022 17:17:10 +0200 Eric Dumazet 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. > > > > I think this is safe. The rose_ftimer_expiry() is an empty function that is > > shown below: > > > > static void rose_ftimer_expiry(struct timer_list *t) > > { > > } > > > > > > > > > > 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. > > > > The rose_stop_t0timer() may hold "rose_node_list_lock" and "rose_neigh_list_lock", > > but the timer handler rose_t0timer_expiry() that is shown below does not need > > these two locks. > > > > static void rose_t0timer_expiry(struct timer_list *t) > > { > > struct rose_neigh *neigh = from_timer(neigh, t, t0timer); > > > > rose_transmit_restart_request(neigh); > > > > neigh->dce_mode = 0; > > > > rose_start_t0timer(neigh); > > This will rearm the timer. del_timer_sync() will not help.
Thank you for your time, but I don't think so.
> Please read the comment in front of del_timer_sync(), in kernel/time/timer.c
I wrote a kernel module to test whether del_timer_sync() could finish a timer handler that use mod_timer() to rewind itself. The following is the result.
# insmod del_timer_sync.ko [ 929.374405] my_timer will be create. [ 929.374738] the jiffies is :4295595572 [ 930.411581] In my_timer_function [ 930.411956] the jiffies is 4295596609 [ 935.466643] In my_timer_function [ 935.467505] the jiffies is 4295601665 [ 940.586538] In my_timer_function [ 940.586916] the jiffies is 4295606784 [ 945.706579] In my_timer_function [ 945.706885] the jiffies is 4295611904
# # rmmod del_timer_sync.ko [ 948.507692] the del_timer_sync is :1 [ 948.507692] # #
The result of the experiment shows that the timer handler could be killed after we execute del_timer_sync(), even if the timer could rewind itself.
Best regards, Duoming Zhou | |