On 10/5/2020 9:08 AM, Christian Eggers wrote:

Between queuing the delayed work and finishing the setup of the dsa ports, the process may sleep in request_module() and the queued work may be executed prior the initialization of the DSA ports is finished. In ksz_mib_read_work(), a NULL dereference will happen within netof_carrier_ok(dp->slave).

Not queuing the delayed work in ksz_init_mib_timer() make things even worse because the work will now be queued for immediate execution (instead of 2000 ms) in ksz_mac_link_down() via dsa_port_link_register_of().

Solution:

1. Do not queue (only initialize) delayed work in ksz_init_mib_timer().
2. Only queue delayed work in ksz_mac_link_down() if init is completed.
3. Queue work once in ksz_switch_register(), after dsa_register_switch()

has completed.

Signed-off-by: Christian Eggers ceggers@arri.de Cc: stable@vger.kernel.org

This looks fine to me and the analysis appears to be correct, don't you need to pair the test for dev->mib_read_internal being non zero with setting it to zero in ksz_switch_unregister()?

You would also most likely want to add a Fixes: tag such that this can be back ported to stable trees?

---

Call tree: ksz9477_i2c_probe() --ksz9477_switch_register() --ksz_switch_register() +--dsa_register_switch() | --dsa_switch_probe() | --dsa_tree_setup() | --dsa_tree_setup_switches() | +--dsa_switch_setup() | | +--ksz9477_setup() | | | --ksz_init_mib_timer() | | | |--/* Start the timer 2 seconds later. */ | | | --schedule_delayed_work(&dev->mib_read, msecs_to_jiffies(2000)); | | --__mdiobus_register() | | --mdiobus_scan() | | --get_phy_device() | | +--get_phy_id() | | --phy_device_create() | | |--/* sleeping, ksz_mib_read_work() can be called meanwhile */ | | --request_module() | | | --dsa_port_setup() | +--/* Called for non-CPU ports */ | +--dsa_slave_create() | | +--/* Too late, ksz_mib_read_work() may be called beforehand */ | | --port->slave = ... | ... | +--Called for CPU port */ | --dsa_port_link_register_of() | --ksz_mac_link_down() | +--/* mib_read must be initialized here */ | +--/* work is already scheduled, so it will be executed after 2000 ms */ | --schedule_delayed_work(&dev->mib_read, 0); -- /* here port->slave is setup properly, scheduling the delayed work should be safe */

static void ksz_mib_read_work() --netif_carrier_ok(dp->slave); dp->slave has not been initialized yet

drivers/net/dsa/microchip/ksz_common.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c index 8e755b50c9c1..a94d2278b95c 100644 --- a/drivers/net/dsa/microchip/ksz_common.c +++ b/drivers/net/dsa/microchip/ksz_common.c @@ -103,14 +103,8 @@ void ksz_init_mib_timer(struct ksz_device *dev) INIT_DELAYED_WORK(&dev->mib_read, ksz_mib_read_work);

• /* Read MIB counters every 30 seconds to avoid overflow. */
• dev->mib_read_interval = msecs_to_jiffies(30000);
• for (i = 0; i < dev->mib_port_cnt; i++) dev->dev_ops->port_init_cnt(dev, i);
• /* Start the timer 2 seconds later. */
• schedule_delayed_work(&dev->mib_read, msecs_to_jiffies(2000)); } EXPORT_SYMBOL_GPL(ksz_init_mib_timer);

@@ -143,7 +137,9 @@ void ksz_mac_link_down(struct dsa_switch *ds, int port, unsigned int mode, /* Read all MIB counters when the link is going down. */ p->read = true;

• schedule_delayed_work(&dev->mib_read, 0);

• /* timer started */
• if (dev->mib_read_interval)

• schedule_delayed_work(&dev->mib_read, 0);
  

  } EXPORT_SYMBOL_GPL(ksz_mac_link_down);

@@ -446,6 +442,12 @@ int ksz_switch_register(struct ksz_device *dev, return ret; }

• /* Read MIB counters every 30 seconds to avoid overflow. */
• dev->mib_read_interval = msecs_to_jiffies(30000);
• /* Start the MIB timer. */
• schedule_delayed_work(&dev->mib_read, 0);
• return 0; } EXPORT_SYMBOL(ksz_switch_register);