[PATCH 4.9 139/240] net: lapbether: Prevent racing when checking whether the netif is running

Greg Kroah-Hartman
2021-05-20T11:15:56Z

From: Xie He <xie.he.0141@gmail.com>

[ Upstream commit 5acd0cfbfbb5a688da1bfb1a2152b0c855115a35 ]

There are two "netif_running" checks in this driver. One is in
"lapbeth_xmit" and the other is in "lapbeth_rcv". They serve to make
sure that the LAPB APIs called in these functions are called before
"lapb_unregister" is called by the "ndo_stop" function.

However, these "netif_running" checks are unreliable, because it's
possible that immediately after "netif_running" returns true, "ndo_stop"
is called (which causes "lapb_unregister" to be called).

This patch adds locking to make sure "lapbeth_xmit" and "lapbeth_rcv" can
reliably check and ensure the netif is running while doing their work.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Xie He <xie.he.0141@gmail.com>
Acked-by: Martin Schiller <ms@dev.tdt.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/wan/lapbether.c | 32 +++++++++++++++++++++++++-------
1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index 666bbacb8cb4..24daa1d0e9c5 100644
--- a/drivers/net/wan/lapbether.c
+++ b/drivers/net/wan/lapbether.c
@@ -56,6 +56,8 @@ struct lapbethdev {
struct list_head node;
struct net_device *ethdev; /* link to ethernet device */
struct net_device *axdev; /* lapbeth device (lapb#) */
+ bool up;
+ spinlock_t up_lock; /* Protects "up" */
};

static LIST_HEAD(lapbeth_devices);
@@ -103,8 +105,9 @@ static int lapbeth_rcv(struct sk_buff *skb, struct net_device *dev, struct packe
rcu_read_lock();
lapbeth = lapbeth_get_x25_dev(dev);
if (!lapbeth)
- goto drop_unlock;
- if (!netif_running(lapbeth->axdev))
+ goto drop_unlock_rcu;
+ spin_lock_bh(&lapbeth->up_lock);
+ if (!lapbeth->up)
goto drop_unlock;

len = skb->data[0] + skb->data[1] * 256;
@@ -119,11 +122,14 @@ static int lapbeth_rcv(struct sk_buff *skb, struct net_device *dev, struct packe
goto drop_unlock;
}
out:
+ spin_unlock_bh(&lapbeth->up_lock);
rcu_read_unlock();
return 0;
drop_unlock:
kfree_skb(skb);
goto out;
+drop_unlock_rcu:
+ rcu_read_unlock();
drop:
kfree_skb(skb);
return 0;
@@ -151,13 +157,11 @@ static int lapbeth_data_indication(struct net_device *dev, struct sk_buff *skb)
static netdev_tx_t lapbeth_xmit(struct sk_buff *skb,
struct net_device *dev)
{
+ struct lapbethdev *lapbeth = netdev_priv(dev);
int err;

- /*
- * Just to be *really* sure not to send anything if the interface
- * is down, the ethernet device may have gone.
- */
- if (!netif_running(dev))
+ spin_lock_bh(&lapbeth->up_lock);
+ if (!lapbeth->up)
goto drop;

/* There should be a pseudo header of 1 byte added by upper layers.
@@ -188,6 +192,7 @@ static netdev_tx_t lapbeth_xmit(struct sk_buff *skb,
goto drop;
}
out:
+ spin_unlock_bh(&lapbeth->up_lock);
return NETDEV_TX_OK;
drop:
kfree_skb(skb);
@@ -279,6 +284,7 @@ static const struct lapb_register_struct lapbeth_callbacks = {
*/
static int lapbeth_open(struct net_device *dev)
{
+ struct lapbethdev *lapbeth = netdev_priv(dev);
int err;

if ((err = lapb_register(dev, &lapbeth_callbacks)) != LAPB_OK) {
@@ -286,13 +292,22 @@ static int lapbeth_open(struct net_device *dev)
return -ENODEV;
}

+ spin_lock_bh(&lapbeth->up_lock);
+ lapbeth->up = true;
+ spin_unlock_bh(&lapbeth->up_lock);
+
return 0;
}

static int lapbeth_close(struct net_device *dev)
{
+ struct lapbethdev *lapbeth = netdev_priv(dev);
int err;

+ spin_lock_bh(&lapbeth->up_lock);
+ lapbeth->up = false;
+ spin_unlock_bh(&lapbeth->up_lock);
+
if ((err = lapb_unregister(dev)) != LAPB_OK)
pr_err("lapb_unregister error: %d\n", err);

@@ -350,6 +365,9 @@ static int lapbeth_new_device(struct net_device *dev)
dev_hold(dev);
lapbeth->ethdev = dev;

+ lapbeth->up = false;
+ spin_lock_init(&lapbeth->up_lock);
+
rc = -EIO;
if (register_netdevice(ndev))
goto fail;
--
2.30.2