On Thu, Feb 4, 2021 at 6:59 AM gregkh@linuxfoundation.org wrote:

The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

This patch only fixes a theoretical race condition. I'm not sure the race condition is really affecting users. Is it necessary to apply this patch to stable branches?

------------------ original commit in Linus's tree ------------------

From b491e6a7391e3ecdebdd7a097550195cc878924a Mon Sep 17 00:00:00 2001 From: Xie He xie.he.0141@gmail.com Date: Mon, 25 Jan 2021 20:09:39 -0800 Subject: [PATCH] net: lapb: Add locking to the lapb module

In the lapb module, the timers may run concurrently with other code in this module, and there is currently no locking to prevent the code from racing on "struct lapb_cb". This patch adds locking to prevent racing.

1. Add "spinlock_t lock" to "struct lapb_cb"; Add "spin_lock_bh" and

"spin_unlock_bh" to APIs, timer functions and notifier functions.

2. Add "bool t1timer_stop, t2timer_stop" to "struct lapb_cb" to make us

able to ask running timers to abort; Modify "lapb_stop_t1timer" and "lapb_stop_t2timer" to make them able to abort running timers; Modify "lapb_t2timer_expiry" and "lapb_t1timer_expiry" to make them abort after they are stopped by "lapb_stop_t1timer", "lapb_stop_t2timer", and "lapb_start_t1timer", "lapb_start_t2timer".

3. Let lapb_unregister wait for other API functions and running timers

to stop.

4. The lapb_device_event function calls lapb_disconnect_request. In

order to avoid trying to hold the lock twice, add a new function named "__lapb_disconnect_request" which assumes the lock is held, and make it called by lapb_disconnect_request and lapb_device_event.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: Martin Schiller ms@dev.tdt.de Signed-off-by: Xie He xie.he.0141@gmail.com Link: https://lore.kernel.org/r/20210126040939.69995-1-xie.he.0141@gmail.com Signed-off-by: Jakub Kicinski kuba@kernel.org

diff --git a/include/net/lapb.h b/include/net/lapb.h index ccc3d1f020b0..eee73442a1ba 100644 --- a/include/net/lapb.h +++ b/include/net/lapb.h @@ -92,6 +92,7 @@ struct lapb_cb { unsigned short n2, n2count; unsigned short t1, t2; struct timer_list t1timer, t2timer;

•   bool                    t1timer_stop, t2timer_stop;
  
    /* Internal control information */
    struct sk_buff_head     write_queue;
  

@@ -103,6 +104,7 @@ struct lapb_cb { struct lapb_frame frmr_data; unsigned char frmr_type;

•   spinlock_t              lock;
    refcount_t              refcnt;
  

};

diff --git a/net/lapb/lapb_iface.c b/net/lapb/lapb_iface.c index 40961889e9c0..0511bbe4af7b 100644 --- a/net/lapb/lapb_iface.c +++ b/net/lapb/lapb_iface.c @@ -122,6 +122,8 @@ static struct lapb_cb *lapb_create_cb(void)

    timer_setup(&lapb->t1timer, NULL, 0);
    timer_setup(&lapb->t2timer, NULL, 0);

•   lapb->t1timer_stop = true;
  

•   lapb->t2timer_stop = true;
  
    lapb->t1      = LAPB_DEFAULT_T1;
    lapb->t2      = LAPB_DEFAULT_T2;
  

@@ -129,6 +131,8 @@ static struct lapb_cb *lapb_create_cb(void) lapb->mode = LAPB_DEFAULT_MODE; lapb->window = LAPB_DEFAULT_WINDOW; lapb->state = LAPB_STATE_0;

•   spin_lock_init(&lapb->lock);
    refcount_set(&lapb->refcnt, 1);
  

out: return lapb; @@ -178,11 +182,23 @@ int lapb_unregister(struct net_device *dev) goto out; lapb_put(lapb);

•   /* Wait for other refs to "lapb" to drop */
  

•   while (refcount_read(&lapb->refcnt) > 2)
  

•           usleep_range(1, 10);
  

•   spin_lock_bh(&lapb->lock);
  

•   lapb_stop_t1timer(lapb);
    lapb_stop_t2timer(lapb);
  
    lapb_clear_queues(lapb);
  
  

•   spin_unlock_bh(&lapb->lock);
  

•   /* Wait for running timers to stop */
  

•   del_timer_sync(&lapb->t1timer);
  

•   del_timer_sync(&lapb->t2timer);
  

•   __lapb_remove_cb(lapb);
  
    lapb_put(lapb);
  

@@ -201,6 +217,8 @@ int lapb_getparms(struct net_device *dev, struct lapb_parms_struct *parms) if (!lapb) goto out;

•   spin_lock_bh(&lapb->lock);
  

•   parms->t1      = lapb->t1 / HZ;
    parms->t2      = lapb->t2 / HZ;
    parms->n2      = lapb->n2;
  

@@ -219,6 +237,7 @@ int lapb_getparms(struct net_device *dev, struct lapb_parms_struct *parms) else parms->t2timer = (lapb->t2timer.expires - jiffies) / HZ;

•   spin_unlock_bh(&lapb->lock);
    lapb_put(lapb);
    rc = LAPB_OK;
  

out: @@ -234,6 +253,8 @@ int lapb_setparms(struct net_device *dev, struct lapb_parms_struct *parms) if (!lapb) goto out;

•   spin_lock_bh(&lapb->lock);
  

•   rc = LAPB_INVALUE;
    if (parms->t1 < 1 || parms->t2 < 1 || parms->n2 < 1)
            goto out_put;
  

@@ -256,6 +277,7 @@ int lapb_setparms(struct net_device *dev, struct lapb_parms_struct *parms)

    rc = LAPB_OK;

out_put:

•   spin_unlock_bh(&lapb->lock);
    lapb_put(lapb);
  

out: return rc; @@ -270,6 +292,8 @@ int lapb_connect_request(struct net_device *dev) if (!lapb) goto out;

•   spin_lock_bh(&lapb->lock);
  

•   rc = LAPB_OK;
    if (lapb->state == LAPB_STATE_1)
            goto out_put;
  

@@ -285,24 +309,18 @@ int lapb_connect_request(struct net_device *dev)

    rc = LAPB_OK;

out_put:

•   spin_unlock_bh(&lapb->lock);
    lapb_put(lapb);
  

out: return rc; } EXPORT_SYMBOL(lapb_connect_request);

-int lapb_disconnect_request(struct net_device *dev) +static int __lapb_disconnect_request(struct lapb_cb *lapb) {

•   struct lapb_cb *lapb = lapb_devtostruct(dev);
  

•   int rc = LAPB_BADTOKEN;
  

•   if (!lapb)
  

•           goto out;
  

•   switch (lapb->state) {
    case LAPB_STATE_0:
  

•           rc = LAPB_NOTCONNECTED;
  

•           goto out_put;
  

•           return LAPB_NOTCONNECTED;
  
    case LAPB_STATE_1:
            lapb_dbg(1, "(%p) S1 TX DISC(1)\n", lapb->dev);
  

@@ -310,12 +328,10 @@ int lapb_disconnect_request(struct net_device *dev) lapb_send_control(lapb, LAPB_DISC, LAPB_POLLON, LAPB_COMMAND); lapb->state = LAPB_STATE_0; lapb_start_t1timer(lapb);

•           rc = LAPB_NOTCONNECTED;
  

•           goto out_put;
  

•           return LAPB_NOTCONNECTED;
  
    case LAPB_STATE_2:
  

•           rc = LAPB_OK;
  

•           goto out_put;
  

•           return LAPB_OK;
    }
  
    lapb_clear_queues(lapb);
  

@@ -328,8 +344,22 @@ int lapb_disconnect_request(struct net_device *dev) lapb_dbg(1, "(%p) S3 DISC(1)\n", lapb->dev); lapb_dbg(0, "(%p) S3 -> S2\n", lapb->dev);

•   rc = LAPB_OK;
  

-out_put:

•   return LAPB_OK;
  

+}

+int lapb_disconnect_request(struct net_device *dev) +{

•   struct lapb_cb *lapb = lapb_devtostruct(dev);
  

•   int rc = LAPB_BADTOKEN;
  

•   if (!lapb)
  

•           goto out;
  

•   spin_lock_bh(&lapb->lock);
  

•   rc = __lapb_disconnect_request(lapb);
  

•   spin_unlock_bh(&lapb->lock);
    lapb_put(lapb);
  

out: return rc; @@ -344,6 +374,8 @@ int lapb_data_request(struct net_device *dev, struct sk_buff *skb) if (!lapb) goto out;

•   spin_lock_bh(&lapb->lock);
  

•   rc = LAPB_NOTCONNECTED;
    if (lapb->state != LAPB_STATE_3 && lapb->state != LAPB_STATE_4)
            goto out_put;
  

@@ -352,6 +384,7 @@ int lapb_data_request(struct net_device *dev, struct sk_buff *skb) lapb_kick(lapb); rc = LAPB_OK; out_put:

•   spin_unlock_bh(&lapb->lock);
    lapb_put(lapb);
  

out: return rc; @@ -364,7 +397,9 @@ int lapb_data_received(struct net_device *dev, struct sk_buff *skb) int rc = LAPB_BADTOKEN;

    if (lapb) {

•           spin_lock_bh(&lapb->lock);
            lapb_data_input(lapb, skb);
  

•           spin_unlock_bh(&lapb->lock);
            lapb_put(lapb);
            rc = LAPB_OK;
    }
  

@@ -435,6 +470,8 @@ static int lapb_device_event(struct notifier_block *this, unsigned long event, if (!lapb) return NOTIFY_DONE;

•   spin_lock_bh(&lapb->lock);
  

•   switch (event) {
    case NETDEV_UP:
            lapb_dbg(0, "(%p) Interface up: %s\n", dev, dev->name);
  

@@ -454,7 +491,7 @@ static int lapb_device_event(struct notifier_block *this, unsigned long event, break; case NETDEV_GOING_DOWN: if (netif_carrier_ok(dev))

•                   lapb_disconnect_request(dev);
  

•                   __lapb_disconnect_request(lapb);
            break;
    case NETDEV_DOWN:
            lapb_dbg(0, "(%p) Interface down: %s\n", dev, dev->name);
  

@@ -489,6 +526,7 @@ static int lapb_device_event(struct notifier_block *this, unsigned long event, break; }

•   spin_unlock_bh(&lapb->lock);
    lapb_put(lapb);
    return NOTIFY_DONE;
  

} diff --git a/net/lapb/lapb_timer.c b/net/lapb/lapb_timer.c index baa247fe4ed0..0230b272b7d1 100644 --- a/net/lapb/lapb_timer.c +++ b/net/lapb/lapb_timer.c @@ -40,6 +40,7 @@ void lapb_start_t1timer(struct lapb_cb *lapb) lapb->t1timer.function = lapb_t1timer_expiry; lapb->t1timer.expires = jiffies + lapb->t1;

•   lapb->t1timer_stop = false;
    add_timer(&lapb->t1timer);
  

}

@@ -50,16 +51,19 @@ void lapb_start_t2timer(struct lapb_cb *lapb) lapb->t2timer.function = lapb_t2timer_expiry; lapb->t2timer.expires = jiffies + lapb->t2;

•   lapb->t2timer_stop = false;
    add_timer(&lapb->t2timer);
  

}

void lapb_stop_t1timer(struct lapb_cb *lapb) {

•   lapb->t1timer_stop = true;
    del_timer(&lapb->t1timer);
  

}

void lapb_stop_t2timer(struct lapb_cb *lapb) {

•   lapb->t2timer_stop = true;
    del_timer(&lapb->t2timer);
  

}

@@ -72,16 +76,31 @@ static void lapb_t2timer_expiry(struct timer_list *t) { struct lapb_cb *lapb = from_timer(lapb, t, t2timer);

•   spin_lock_bh(&lapb->lock);
  

•   if (timer_pending(&lapb->t2timer)) /* A new timer has been set up */
  

•           goto out;
  

•   if (lapb->t2timer_stop) /* The timer has been stopped */
  

•           goto out;
  

•   if (lapb->condition & LAPB_ACK_PENDING_CONDITION) {
            lapb->condition &= ~LAPB_ACK_PENDING_CONDITION;
            lapb_timeout_response(lapb);
    }
  

+out:

•   spin_unlock_bh(&lapb->lock);
  

}

static void lapb_t1timer_expiry(struct timer_list *t) { struct lapb_cb *lapb = from_timer(lapb, t, t1timer);

•   spin_lock_bh(&lapb->lock);
  

•   if (timer_pending(&lapb->t1timer)) /* A new timer has been set up */
  

•           goto out;
  

•   if (lapb->t1timer_stop) /* The timer has been stopped */
  

•           goto out;
  

•   switch (lapb->state) {
  
            /*
  

@@ -108,7 +127,7 @@ static void lapb_t1timer_expiry(struct timer_list *t) lapb->state = LAPB_STATE_0; lapb_disconnect_indication(lapb, LAPB_TIMEDOUT); lapb_dbg(0, "(%p) S1 -> S0\n", lapb->dev);

•                           return;
  

•                           goto out;
                    } else {
                            lapb->n2count++;
                            if (lapb->mode & LAPB_EXTENDED) {
  

@@ -132,7 +151,7 @@ static void lapb_t1timer_expiry(struct timer_list *t) lapb->state = LAPB_STATE_0; lapb_disconnect_confirmation(lapb, LAPB_TIMEDOUT); lapb_dbg(0, "(%p) S2 -> S0\n", lapb->dev);

•                           return;
  

•                           goto out;
                    } else {
                            lapb->n2count++;
                            lapb_dbg(1, "(%p) S2 TX DISC(1)\n", lapb->dev);
  

@@ -150,7 +169,7 @@ static void lapb_t1timer_expiry(struct timer_list *t) lapb_stop_t2timer(lapb); lapb_disconnect_indication(lapb, LAPB_TIMEDOUT); lapb_dbg(0, "(%p) S3 -> S0\n", lapb->dev);

•                           return;
  

•                           goto out;
                    } else {
                            lapb->n2count++;
                            lapb_requeue_frames(lapb);
  

@@ -167,7 +186,7 @@ static void lapb_t1timer_expiry(struct timer_list *t) lapb->state = LAPB_STATE_0; lapb_disconnect_indication(lapb, LAPB_TIMEDOUT); lapb_dbg(0, "(%p) S4 -> S0\n", lapb->dev);

•                           return;
  

•                           goto out;
                    } else {
                            lapb->n2count++;
                            lapb_transmit_frmr(lapb);
  

@@ -176,4 +195,7 @@ static void lapb_t1timer_expiry(struct timer_list *t) }

    lapb_start_t1timer(lapb);

+out:

•   spin_unlock_bh(&lapb->lock);
  

}