| 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: <Yxx5sJh/TLzSR5xU@x-berg.in-berlin.de>
Date: Sat, 10 Sep 2022 13:49:04 +0200
From: Thomas Osterried <thomas@...erried.de>
To: Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>
Cc: "David S . Miller" <davem@...emloft.net>,
Paolo Abeni <pabeni@...hat.com>,
Bernard Pidoux <f6bvp@...e.fr>,
Duoming Zhou <duoming@....edu.cn>, netdev@...r.kernel.org,
linux-hams@...r.kernel.org
Subject: Re: [AX25] patch did not fix -- was: ax25: fix incorrect
dev_tracker usage
Hello,
please allow me the question what the patch tries to fix.
1. we add sessions to the list of active sessions ax25_cb_add(ax25),
and remove them on close.
Why do we need a tracker?
2. ax25_dev.c:
ax25_dev_device_up():
netdev_hold(dev, &ax25_dev->dev_tracker, GFP_KERNEL);
ax25_dev_device_down():
netdev_put(dev, &ax25_dev->dev_tracker);
ax25_dev_free():
netdev_put(ax25_dev->dev, &ax25_dev->dev_tracker);
Just to be sure: It's the list of active ax25-interface, correct?
-> Looks good to me.
3. On device status change, i.e. NETDEV_DOWN, ax25_device_event() calls
ax25_kill_by_device(dev)
and
ax25_dev_device_down(dev) (we saw in 2)).
Before patches
7c6327c77d509e78bff76f2a4551fcfee851682e / d7c4c9e075f8cc6d88d277bc24e5d99297f03c06
we did
in ax25_relase(): netdev_put(ax25_dev->dev, &ax25_dev->dev_tracker);
and
in ax25_bind(); netdev_hold(ax25_dev->dev, &ax25_dev->dev_tracker, GFP_ATOMIC);
ax25_kill_by_device() traverses through the list of active connections
(ax25_list):
if (sk->sk_socket) {
netdev_put(ax25_dev->dev,
&ax25_dev->dev_tracker);
ax25_dev_put(ax25_dev);
}
The patches mentioned above were:
ax25_release(): netdev_put(ax25_dev->dev, &ax25->dev_tracker);
ax25_bind(): netdev_hold(ax25_dev->dev, &ax25->dev_tracker, GFP_ATOMIC);
-> Previously, each session (ax25_cb) was added to it's device with the
dev_tracker of the _device_ (&ax25_dev->dev_tracker)
Now, each session (ax25_cb) is added with it's own dev_tracker
&ax25->dev_tracker
But:
ax25_kill_by_device() goes through the list of active sessions and
does
netdev_put(ax25_dev->dev, &ax25_dev->dev_tracker);
instead of the new concept; I would have expected:
netdev_put(ax25_dev->dev, &s->dev_tracker);
If we netdev_put() to a non-existent tracker, this may explain
the warnings
unregister_netdevice: waiting for bpq1 to become free. Usage count = -2
and
refcount_t: underflow; use-after-free.
that I observed in my previous mail.
4. Again, my question for understanding about the dev_tracker concept:
should _all_ in- and outgoing sessions be tracked?
If so, I argue we have to add
- new outbound sessions to the tracker (i.E. if a IP mode VC frame is
sent)
- new inbound sessions to the tracker
Also, ax25_bind() currently does not track all sessions:
/*
* User already set interface with SO_BINDTODEVICE
*/
if (ax25->ax25_dev != NULL)
goto done;
...
if (ax25_dev) {
ax25_fillin_cb(ax25, ax25_dev);
netdev_hold(ax25_dev->dev, &ax25->dev_tracker, GFP_ATOMIC);
}
done:
ax25_cb_add(ax25);
-> If user has previously called ax25_setsockopt() with SO_BINDTODEVICE,
the device has been added to ax25->ax25_dev. But ax25_bind() does not
add it to the tracker list (see above, ax25->ax25_dev is != NULL).
ax25_connect() does also currently not track all sessions:
There's a spcial condition sock_flag(sk, SOCK_ZAPPED), where connect()
is allowed to be called without having gone through ax25_bind().
Via ax25_rt_autobind(ax25, ..) it get's the appropriete ax25>dev.
-> ax25_fillin_cb(ax25, ax25->ax25_dev);
ax25_cb_add(ax25);
=> No tracker is added for this session.
ax25_kill_by_device() does remove the tracker. I argued above, it removes
the wrong tracker here:
if (sk->sk_socket) {
netdev_put(ax25_dev->dev,
&ax25_dev->dev_tracker);
ax25_dev_put(ax25_dev);
}
..instead of &s->dev_tracker.
And if we have trackers for all sessions (not only those that came via
ax25_bind() from userspace), it's not enough to remove the tracker only
for sessions with sk->socket.
-> I would have expeted
ax25_for_each(s, &ax25_list) {
if (s->ax25_dev == ax25_dev) {
if (s->ax25_dev == ax25_dev) {
netdev_put(ax25_dev->dev, &s->dev_tracker);
...
Finally:
On normal session close (userspace program, or idle timer expiry),
we need to have timers running for correct AX.25-session-close:
If we are in connected state (AX25_STATE_3 or AX25_STATE_4), we need
to send DISC in interval until max retry reached, or until we receive
a DM-).
In ax25_release(), we see:
if (ax25_dev) {
...
netdev_put(ax25_dev->dev, &ax25->dev_tracker);
ax25_dev_put(ax25_dev);
But we need have timers running for ax25_cb's that still refer to
the network dev (and need to be there until correct session
termination), we have a conflict here, because
netdev_put() assures here we are not allowed to refer to the
dev anymore.
That needs to be resolved.
Context:
diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index bbac3cb4dc99d..d82a51e69386b 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -1066,7 +1066,7 @@ static int ax25_release(struct socket *sock)
del_timer_sync(&ax25->t3timer);
del_timer_sync(&ax25->idletimer);
}
- netdev_put(ax25_dev->dev, &ax25_dev->dev_tracker);
+ netdev_put(ax25_dev->dev, &ax25->dev_tracker);
ax25_dev_put(ax25_dev);
}
@@ -1147,7 +1147,7 @@ static int ax25_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
if (ax25_dev) {
ax25_fillin_cb(ax25, ax25_dev);
- netdev_hold(ax25_dev->dev, &ax25_dev->dev_tracker, GFP_ATOMIC);
+ netdev_hold(ax25_dev->dev, &ax25->dev_tracker, GFP_ATOMIC);
}
done:
Powered by blists - more mailing lists