From: Duoming Zhou <duoming@zju.edu.cn>
To: linux-hams@vger.kernel.org
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
kuba@kernel.org, davem@davemloft.net, ralf@linux-mips.org,
jreuter@yaina.de, dan.carpenter@oracle.com,
Duoming Zhou <duoming@zju.edu.cn>
Subject: [PATCH net V4 2/2] ax25: Fix NULL pointer dereferences in ax25 timers
Date: Tue, 15 Mar 2022 09:56:54 +0800 [thread overview]
Message-ID: <20220315015654.79941-1-duoming@zju.edu.cn> (raw)
There are race conditions that may lead to null pointer dereferences in
ax25_heartbeat_expiry(), ax25_t1timer_expiry(), ax25_t2timer_expiry(),
ax25_t3timer_expiry() and ax25_idletimer_expiry(), when we use
ax25_kill_by_device() to detach the ax25 device.
One of the race conditions that cause null pointer dereferences can be
shown as below:
(Thread 1) | (Thread 2)
ax25_connect() |
ax25_std_establish_data_link() |
ax25_start_t1timer() |
mod_timer(&ax25->t1timer,..) |
| ax25_kill_by_device()
(wait a time) | ...
| s->ax25_dev = NULL; //(1)
ax25_t1timer_expiry() |
ax25->ax25_dev->values[..] //(2)| ...
... |
We set null to ax25_cb->ax25_dev in position (1) and dereference
the null pointer in position (2).
The corresponding fail log is shown below:
===============================================================
BUG: kernel NULL pointer dereference, address: 0000000000000050
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.17.0-rc6-00794-g45690b7d0
RIP: 0010:ax25_t1timer_expiry+0x12/0x40
...
Call Trace:
call_timer_fn+0x21/0x120
__run_timers.part.0+0x1ca/0x250
run_timer_softirq+0x2c/0x60
__do_softirq+0xef/0x2f3
irq_exit_rcu+0xb6/0x100
sysvec_apic_timer_interrupt+0xa2/0xd0
...
This patch uses ax25_disconnect() to delete timers before we set null to
ax25_cb->ax25_dev in ax25_kill_by_device().The function ax25_disconnect()
will not return until all timers are stopped, because we have changed
del_timer() to del_timer_sync(). What`s more, we add condition check in
ax25_destroy_socket(), because ax25_stop_heartbeat() will not return,
if there is still heartbeat.
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
---
Changes in V4:
- Based on [PATCH net V4 1/2] ax25: Fix refcount leaks caused by ax25_cb_del().
net/ax25/af_ax25.c | 7 ++++---
net/ax25/ax25_timer.c | 10 +++++-----
2 files changed, 9 insertions(+), 8 deletions(-)
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index 0886109421a..dc6161a75a1 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -89,20 +89,20 @@ static void ax25_kill_by_device(struct net_device *dev)
sk = s->sk;
if (!sk) {
spin_unlock_bh(&ax25_list_lock);
- s->ax25_dev = NULL;
ax25_disconnect(s, ENETUNREACH);
+ s->ax25_dev = NULL;
spin_lock_bh(&ax25_list_lock);
goto again;
}
sock_hold(sk);
spin_unlock_bh(&ax25_list_lock);
lock_sock(sk);
+ ax25_disconnect(s, ENETUNREACH);
s->ax25_dev = NULL;
if (sk->sk_wq) {
dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
ax25_dev_put(ax25_dev);
}
- ax25_disconnect(s, ENETUNREACH);
release_sock(sk);
spin_lock_bh(&ax25_list_lock);
sock_put(sk);
@@ -307,7 +307,8 @@ void ax25_destroy_socket(ax25_cb *ax25)
ax25_cb_del(ax25);
- ax25_stop_heartbeat(ax25);
+ if (!ax25->sk || !sock_flag(ax25->sk, SOCK_DESTROY))
+ ax25_stop_heartbeat(ax25);
ax25_stop_t1timer(ax25);
ax25_stop_t2timer(ax25);
ax25_stop_t3timer(ax25);
diff --git a/net/ax25/ax25_timer.c b/net/ax25/ax25_timer.c
index 85865ebfdfa..99af3d1aeec 100644
--- a/net/ax25/ax25_timer.c
+++ b/net/ax25/ax25_timer.c
@@ -78,27 +78,27 @@ void ax25_start_idletimer(ax25_cb *ax25)
void ax25_stop_heartbeat(ax25_cb *ax25)
{
- del_timer(&ax25->timer);
+ del_timer_sync(&ax25->timer);
}
void ax25_stop_t1timer(ax25_cb *ax25)
{
- del_timer(&ax25->t1timer);
+ del_timer_sync(&ax25->t1timer);
}
void ax25_stop_t2timer(ax25_cb *ax25)
{
- del_timer(&ax25->t2timer);
+ del_timer_sync(&ax25->t2timer);
}
void ax25_stop_t3timer(ax25_cb *ax25)
{
- del_timer(&ax25->t3timer);
+ del_timer_sync(&ax25->t3timer);
}
void ax25_stop_idletimer(ax25_cb *ax25)
{
- del_timer(&ax25->idletimer);
+ del_timer_sync(&ax25->idletimer);
}
int ax25_t1timer_running(ax25_cb *ax25)
--
2.17.1
next reply other threads:[~2022-03-15 1:57 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-15 1:56 Duoming Zhou [this message]
2022-03-15 3:02 ` [PATCH net V4 2/2] ax25: Fix NULL pointer dereferences in ax25 timers Eric Dumazet
2022-03-15 16:30 ` 周多明
2022-03-16 4:32 ` 周多明
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