Affected: Alpaquita:stream: linux-lts

In the Linux kernel, the following vulnerability has been resolved:

linkwatch: use __dev_put() in callers to prevent UAF

After linkwatch_do_dev() calls __dev_put() to release the linkwatch reference, the device refcount may drop to 1. At this point, netdev_run_todo() can proceed (since linkwatch_sync_dev() sees an empty list and returns without blocking), wait for the refcount to become 1 via netdev_wait_allrefs_any(), and then free the device via kobject_put().

This creates a use-after-free when __linkwatch_run_queue() tries to call netdev_unlock_ops() on the already-freed device.

Note that adding netdev_lock_ops()/netdev_unlock_ops() pair in netdev_run_todo() before kobject_put() would not work, because netdev_lock_ops() is conditional - it only locks when netdev_need_ops_lock() returns true. If the device doesn't require ops_lock, linkwatch won't hold any lock, and netdev_run_todo() acquiring the lock won't provide synchronization.

Fix this by moving __dev_put() from linkwatch_do_dev() to its callers. The device reference logically pairs with de-listing the device, so it's reasonable for the caller that did the de-listing to release it. This allows placing __dev_put() after all device accesses are complete, preventing UAF.

The bug can be reproduced by adding mdelay(2000) after linkwatch_do_dev() in __linkwatch_run_queue(), then running:

ip tuntap add mode tun name tun_test ip link set tun_test up ip link set tun_test carrier off ip link set tun_test carrier…

In the Linux kernel, the following vulnerability has been resolved:

linkwatch: use __dev_put() in callers to prevent UAF

After linkwatch_do_dev() calls __dev_put() to release the linkwatch reference, the device refcount may drop to 1. At this point, netdev_run_todo() can proceed (since linkwatch_sync_dev() sees an empty list and returns without blocking), wait for the refcount to become 1 via netdev_wait_allrefs_any(), and then free the device via kobject_put().

This creates a use-after-free when __linkwatch_run_queue() tries to call netdev_unlock_ops() on the already-freed device.

Note that adding netdev_lock_ops()/netdev_unlock_ops() pair in netdev_run_todo() before kobject_put() would not work, because netdev_lock_ops() is conditional - it only locks when netdev_need_ops_lock() returns true. If the device doesn't require ops_lock, linkwatch won't hold any lock, and netdev_run_todo() acquiring the lock won't provide synchronization.

Fix this by moving __dev_put() from linkwatch_do_dev() to its callers. The device reference logically pairs with de-listing the device, so it's reasonable for the caller that did the de-listing to release it. This allows placing __dev_put() after all device accesses are complete, preventing UAF.

The bug can be reproduced by adding mdelay(2000) after linkwatch_do_dev() in __linkwatch_run_queue(), then running:

ip tuntap add mode tun name tun_test ip link set tun_test up ip link set tun_test carrier off ip link set tun_test carrier…

Affected: Ubuntu:16.04:LTS: linux-hwe-edge, Ubuntu:18.04:LTS: linux-aws-5.0, Ubuntu:18.04:LTS: linux-aws-5.3, Ubuntu:18.04:LTS: linux-azure, Ubuntu:18.04:LTS: linux-azure-5.3, Ubuntu:18.04:LTS: linux-azure-edge, Ubuntu:18.04:LTS: linux-gcp, Ubuntu:18.04:LTS: linux-gcp-5.3, Ubuntu:18.04:LTS: linux-gke-4.15, Ubuntu:18.04:LTS: linux-gke-5.4 and 99 more

In the Linux kernel, the following vulnerability has been resolved: linkwatch: use __dev_put() in callers to prevent UAF After linkwatch_do_dev() calls __dev_put() to release the linkwatch reference, the device refcount may drop to 1. At this point, netdev_run_todo() can proceed (since linkwatch_sync_dev() sees an empty list and returns without blocking), wait for the refcount to become 1 via netdev_wait_allrefs_any(), and then free the device via kobject_put(). This creates a use-after-free when __linkwatch_run_queue() tries to call netdev_unlock_ops() on the already-freed device. Note that adding netdev_lock_ops()/netdev_unlock_ops() pair in netdev_run_todo() before kobject_put() would not work, because netdev_lock_ops() is conditional - it only locks when netdev_need_ops_lock() returns true. If the device doesn't require ops_lock, linkwatch won't hold any lock, and netdev_run_todo() acquiring the lock won't provide synchronization. Fix this by moving __dev_put() from linkwatch_do_dev() to its callers. The device reference logically pairs with de-listing the device, so it's reasonable for the caller that did the de-listing to release it. This allows placing __dev_put() after all device accesses are complete, preventing UAF. The bug can be reproduced by adding mdelay(2000) after linkwatch_do_dev() in __linkwatch_run_queue(), then running: ip tuntap add mode tun name tun_test ip link set tun_test up ip link set tun_test carrier off ip link set tun_test carrier on s…

Ein Angreifer kann mehrere Schwachstellen im Linux-Kernel ausnutzen, um nicht näher spezifizierte Angriffe durchzuführen, die möglicherweise zu einer Denial-of-Service- Bedingung führen oder eine Speicherbeschädigung verursachen können.