On Thu, Feb 4, 2021 at 6:59 AM <gregkh@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>.
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@xxxxxxxxx>
> 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@xxxxxxxxxx>
> Signed-off-by: Xie He <xie.he.0141@xxxxxxxxx>
> Link: https://lore.kernel.org/r/20210126040939.69995-1-xie.he.0141@xxxxxxxxx
> Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
>
> 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);
> }
>
