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Subject[PATCH net] net: rose: fix UAF bug caused by rose_t0timer_expiry
Date
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);
}

void rose_stop_t0timer(struct rose_neigh *neigh)
{
- del_timer(&neigh->t0timer);
+ del_timer_sync(&neigh->t0timer);
}

int rose_ftimer_running(struct rose_neigh *neigh)
--
2.17.1
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