Messages in this thread Patch in this message | | | From | Duoming Zhou <> | Subject | [PATCH net V4 2/2] ax25: Fix NULL pointer dereferences in ax25 timers | Date | Tue, 15 Mar 2022 09:56:54 +0800 |
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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
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