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ax25: Fix ax25 session cleanup problems 

There are session cleanup problems in ax25_release() and
ax25_disconnect(). If we setup a session and then disconnect,
the disconnected session is still in "LISTENING" state that
is shown below.

Active AX.25 sockets
Dest       Source     Device  State        Vr/Vs    Send-Q  Recv-Q
DL9SAU-4   DL9SAU-3   ???     LISTENING    000/000  0       0
DL9SAU-3   DL9SAU-4   ???     LISTENING    000/000  0       0

The first reason is caused by del_timer_sync() in ax25_release().
The timers of ax25 are used for correct session cleanup. If we use
ax25_release() to close ax25 sessions and ax25_dev is not null,
the del_timer_sync() functions in ax25_release() will execute.
As a result, the sessions could not be cleaned up correctly,
because the timers have stopped.

In order to solve this problem, this patch adds a device_up flag
in ax25_dev in order to judge whether the device is up. If there
are sessions to be cleaned up, the del_timer_sync() in
ax25_release() will not execute. What's more, we add ax25_cb_del()
in ax25_kill_by_device(), because the timers have been stopped
and there are no functions that could delete ax25_cb if we do not
call ax25_release(). Finally, we reorder the position of
ax25_list_lock in ax25_cb_del() in order to synchronize among
different functions that call ax25_cb_del().

The second reason is caused by improper check in ax25_disconnect().
The incoming ax25 sessions which ax25->sk is null will close
heartbeat timer, because the check "if(!ax25->sk || ..)" is
satisfied. As a result, the session could not be cleaned up properly.

In order to solve this problem, this patch changes the improper
check to "if(ax25->sk && ..)" in ax25_disconnect().

What`s more, the ax25_disconnect() may be called twice, which is
not necessary. For example, ax25_kill_by_device() calls
ax25_disconnect() and sets ax25->state to AX25_STATE_0, but
ax25_release() calls ax25_disconnect() again.

In order to solve this problem, this patch add a check in
ax25_release(). If the flag of ax25->sk equals to SOCK_DEAD,
the ax25_disconnect() in ax25_release() should not be executed.

Fixes: 82e31755e5 ("ax25: Fix UAF bugs in ax25 timers")
Fixes: 8a367e74c0 ("ax25: Fix segfault after sock connection timeout")
Reported-and-tested-by: Thomas Osterried <thomas@osterried.de>
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Link: https://lore.kernel.org/r/20220530152158.108619-1-duoming@zju.edu.cn
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Duoming Zhou 2022-05-30 23:21:58 +08:00 committed by Paolo Abeni
parent 9f4fc18bf2
commit 7d8a3a477b
4 changed files with 20 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/net/ax25.h
View File

@ -228,6 +228,7 @@ typedef struct ax25_dev {
ax25_dama_info dama;
#endif
refcount_t refcount;
bool device_up;
} ax25_dev;
typedef struct ax25_cb {

27
net/ax25/af_ax25.c
View File

@ -62,12 +62,12 @@ static void ax25_free_sock(struct sock *sk)
*/
static void ax25_cb_del(ax25_cb *ax25)
{
spin_lock_bh(&ax25_list_lock);
if (!hlist_unhashed(&ax25->ax25_node)) {
spin_lock_bh(&ax25_list_lock);
hlist_del_init(&ax25->ax25_node);
spin_unlock_bh(&ax25_list_lock);
ax25_cb_put(ax25);
}
spin_unlock_bh(&ax25_list_lock);
}
/*
@ -81,6 +81,7 @@ static void ax25_kill_by_device(struct net_device *dev)
if ((ax25_dev = ax25_dev_ax25dev(dev)) == NULL)
return;
ax25_dev->device_up = false;
spin_lock_bh(&ax25_list_lock);
again:
@ -91,6 +92,7 @@ again:
spin_unlock_bh(&ax25_list_lock);
ax25_disconnect(s, ENETUNREACH);
s->ax25_dev = NULL;
ax25_cb_del(s);
spin_lock_bh(&ax25_list_lock);
goto again;
}
@ -103,6 +105,7 @@ again:
dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
ax25_dev_put(ax25_dev);
}
ax25_cb_del(s);
release_sock(sk);
spin_lock_bh(&ax25_list_lock);
sock_put(sk);
@ -995,9 +998,11 @@ static int ax25_release(struct socket *sock)
if (sk->sk_type == SOCK_SEQPACKET) {
switch (ax25->state) {
case AX25_STATE_0:
release_sock(sk);
ax25_disconnect(ax25, 0);
lock_sock(sk);
if (!sock_flag(ax25->sk, SOCK_DEAD)) {
release_sock(sk);
ax25_disconnect(ax25, 0);
lock_sock(sk);
}
ax25_destroy_socket(ax25);
break;
@ -1053,11 +1058,13 @@ static int ax25_release(struct socket *sock)
ax25_destroy_socket(ax25);
}
if (ax25_dev) {
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);
if (!ax25_dev->device_up) {
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);
}
dev_put_track(ax25_dev->dev, &ax25_dev->dev_tracker);
ax25_dev_put(ax25_dev);
}

1
net/ax25/ax25_dev.c
View File

@ -62,6 +62,7 @@ void ax25_dev_device_up(struct net_device *dev)
ax25_dev->dev = dev;
dev_hold_track(dev, &ax25_dev->dev_tracker, GFP_ATOMIC);
ax25_dev->forward = NULL;
ax25_dev->device_up = true;
ax25_dev->values[AX25_VALUES_IPDEFMODE] = AX25_DEF_IPDEFMODE;
ax25_dev->values[AX25_VALUES_AXDEFMODE] = AX25_DEF_AXDEFMODE;

2
net/ax25/ax25_subr.c
View File

@ -268,7 +268,7 @@ void ax25_disconnect(ax25_cb *ax25, int reason)
del_timer_sync(&ax25->t3timer);
del_timer_sync(&ax25->idletimer);
} else {
if (!ax25->sk || !sock_flag(ax25->sk, SOCK_DESTROY))
if (ax25->sk && !sock_flag(ax25->sk, SOCK_DESTROY))
ax25_stop_heartbeat(ax25);
ax25_stop_t1timer(ax25);
ax25_stop_t2timer(ax25);