| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <e552387.5e93.17f90fff974.Coremail.duoming@zju.edu.cn>
Date: Wed, 16 Mar 2022 12:32:49 +0800 (GMT+08:00)
From: 周多明 <duoming@....edu.cn>
To: "Eric Dumazet" <eric.dumazet@...il.com>
Cc: linux-hams@...r.kernel.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, kuba@...nel.org, davem@...emloft.net,
ralf@...ux-mips.org, jreuter@...na.de
Subject: Re: Re: [PATCH net V4 2/2] ax25: Fix NULL pointer dereferences in
ax25 timers
Hello,
On Mon, 14 Mar 2022 20:03:00 -0700, Eric Dumazet wrote:
> > 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@....edu.cn>
>
> Missing FIxes: tag ?
>
>
> > ---
> > 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)
>
>
>
> Are you sure calling del_time_sync() wont deadlock ?
>
>
> If the timer handlers need a lock owned by the thread calling
> del_timer_sync(),
>
> then this will block forever.
In other to lower the impact to other functions, I come up with the following
patch.
If ax25_disconnect() is called by ax25_kill_by_device() or ax25->ax25_dev
is NULL, the reason in ax25_disconnect() will be equal to ENETUNREACH.
This patch adds check and uses del_timer_sync() to delete timers in
ax25_disconnect(), it will wait all timers to stop before we set null
to ax25_cb->ax25_dev in ax25_kill_by_device().
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index cf8847cfc66..992b6e5d85d 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_socket) {
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);
diff --git a/net/ax25/ax25_subr.c b/net/ax25/ax25_subr.c
index 15ab812c4fe..3a476e4f6cd 100644
--- a/net/ax25/ax25_subr.c
+++ b/net/ax25/ax25_subr.c
@@ -261,12 +261,20 @@ void ax25_disconnect(ax25_cb *ax25, int reason)
{
ax25_clear_queues(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);
- ax25_stop_idletimer(ax25);
+ if (reason == ENETUNREACH) {
+ del_timer_sync(&ax25->timer);
+ del_timer_sync(&ax25->t1timer);
+ del_timer_sync(&ax25->t2timer);
+ del_timer_sync(&ax25->t3timer);
+ del_timer_sync(&ax25->idletimer);
+ } else {
+ 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);
+ ax25_stop_idletimer(ax25);
+ }
ax25->state = AX25_STATE_0;
--
2.17.1
Do you think this patch is ok?
Best wishes,
Duoming Zhou
Powered by blists - more mailing lists