[PATCH 5.4 07/38] net: rose: fix UAF bug caused by rose_t0timer_expiry

From: Greg Kroah-Hartman
Date: Mon Jul 11 2022 - 05:16:17 EST

From: Duoming Zhou <duoming@xxxxxxxxxx>

commit 148ca04518070910739dfc4eeda765057856403d upstream.

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:
? expire_timers+0x144/0x320
? expire_timers+0x144/0x320

This patch changes rose_stop_ftimer() and rose_stop_t0timer()
in rose_remove_neigh() 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@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20220705125610.77971-1-duoming@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/rose/rose_route.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/net/rose/rose_route.c
+++ b/net/rose/rose_route.c
@@ -227,8 +227,8 @@ static void rose_remove_neigh(struct ros
struct rose_neigh *s;

- rose_stop_ftimer(rose_neigh);
- rose_stop_t0timer(rose_neigh);
+ del_timer_sync(&rose_neigh->ftimer);
+ del_timer_sync(&rose_neigh->t0timer);