From: Sasha Levin <sashal@kernel•org>
To: linux-kernel@vger•kernel.org, stable@vger•kernel.org
Cc: Duoming Zhou <duoming@zju•edu.cn>, Lin Ma <linma@zju•edu.cn>,
"David S . Miller" <davem@davemloft•net>,
Sasha Levin <sashal@kernel•org>,
ajk@comnets•uni-bremen.de, kuba@kernel•org,
linux-hams@vger•kernel.org, netdev@vger•kernel.org
Subject: [PATCH AUTOSEL 5.16 13/28] drivers: hamradio: 6pack: fix UAF bug caused by mod_timer()
Date: Tue, 1 Mar 2022 15:13:18 -0500 [thread overview]
Message-ID: <20220301201344.18191-13-sashal@kernel.org> (raw)
In-Reply-To: <20220301201344.18191-1-sashal@kernel.org>
From: Duoming Zhou <duoming@zju•edu.cn>
[ Upstream commit efe4186e6a1b54bf38b9e05450d43b0da1fd7739 ]
When a 6pack device is detaching, the sixpack_close() will act to cleanup
necessary resources. Although del_timer_sync() in sixpack_close()
won't return if there is an active timer, one could use mod_timer() in
sp_xmit_on_air() to wake up timer again by calling userspace syscall such
as ax25_sendmsg(), ax25_connect() and ax25_ioctl().
This unexpected waked handler, sp_xmit_on_air(), realizes nothing about
the undergoing cleanup and may still call pty_write() to use driver layer
resources that have already been released.
One of the possible race conditions is shown below:
(USE) | (FREE)
ax25_sendmsg() |
ax25_queue_xmit() |
... |
sp_xmit() |
sp_encaps() | sixpack_close()
sp_xmit_on_air() | del_timer_sync(&sp->tx_t)
mod_timer(&sp->tx_t,...) | ...
| unregister_netdev()
| ...
(wait a while) | tty_release()
| tty_release_struct()
| release_tty()
sp_xmit_on_air() | tty_kref_put(tty_struct) //FREE
pty_write(tty_struct) //USE | ...
The corresponding fail log is shown below:
===============================================================
BUG: KASAN: use-after-free in __run_timers.part.0+0x170/0x470
Write of size 8 at addr ffff88800a652ab8 by task swapper/2/0
...
Call Trace:
...
queue_work_on+0x3f/0x50
pty_write+0xcd/0xe0pty_write+0xcd/0xe0
sp_xmit_on_air+0xb2/0x1f0
call_timer_fn+0x28/0x150
__run_timers.part.0+0x3c2/0x470
run_timer_softirq+0x3b/0x80
__do_softirq+0xf1/0x380
...
This patch reorders the del_timer_sync() after the unregister_netdev()
to avoid UAF bugs. Because the unregister_netdev() is well synchronized,
it flushs out any pending queues, waits the refcount of net_device
decreases to zero and removes net_device from kernel. There is not any
running routines after executing unregister_netdev(). Therefore, we could
not arouse timer from userspace again.
Signed-off-by: Duoming Zhou <duoming@zju•edu.cn>
Reviewed-by: Lin Ma <linma@zju•edu.cn>
Signed-off-by: David S. Miller <davem@davemloft•net>
Signed-off-by: Sasha Levin <sashal@kernel•org>
---
drivers/net/hamradio/6pack.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/net/hamradio/6pack.c b/drivers/net/hamradio/6pack.c
index 8a19a06b505d1..ff2bb3d80fac8 100644
--- a/drivers/net/hamradio/6pack.c
+++ b/drivers/net/hamradio/6pack.c
@@ -668,11 +668,11 @@ static void sixpack_close(struct tty_struct *tty)
*/
netif_stop_queue(sp->dev);
+ unregister_netdev(sp->dev);
+
del_timer_sync(&sp->tx_t);
del_timer_sync(&sp->resync_t);
- unregister_netdev(sp->dev);
-
/* Free all 6pack frame buffers after unreg. */
kfree(sp->rbuff);
kfree(sp->xbuff);
--
2.34.1
next prev parent reply other threads:[~2022-03-01 20:15 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-01 20:13 [PATCH AUTOSEL 5.16 01/28] selftests/bpf: Add test for bpf_timer overwriting crash Sasha Levin
2022-03-01 20:13 ` Sasha Levin [this message]
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 14/28] net-sysfs: add check for netdevice being present to speed_show Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 15/28] sr9700: sanity check for packet length Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 21/28] Revert "xen-netback: remove 'hotplug-status' once it has served its purpose" Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 22/28] Revert "xen-netback: Check for hotplug-status existence before watching" Sasha Levin
2022-03-01 20:13 ` [PATCH AUTOSEL 5.16 23/28] ipv6: prevent a possible race condition with lifetimes Sasha Levin
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