Affected: Linux

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

gpio: sloppy-logic-analyzer: fix use-after-free via debugfs trigger on unbind

The "trigger" debugfs file has a hand-rolled ->write handler (trigger_write()) that dereferences the per-device gpio_la_poll_priv. The file is created with debugfs_create_file_unsafe(), and the handler never takes a debugfs reference. Nothing keeps the object alive while the handler runs.

priv is allocated with devm_kzalloc(). devres frees it when the platform device is unbound. debugfs_create_file_unsafe() installs no full_proxy wrapper, so debugfs_remove_recursive() in gpio_la_poll_remove() does not wait for an in-flight trigger_write(). The blob_lock taken there does not help, because trigger_write() never takes it. A write that races an unbind therefore writes into freed memory:

trigger_write() gpio_la_poll_remove() priv = m->private buf = memdup_user() [may sleep] mutex_lock(&priv->blob_lock) debugfs_remove_recursive() [no wait] mutex_unlock(&priv->blob_lock) (remove returns; devres frees priv) priv->trig_data = buf <-- use-after-free write priv->trig_len = count

The race is reachable by root via /sys/bus/platform/drivers/gpio-sloppy-logic-analyzer/unbind.

Create "trigger" with debugfs_create_file() instead. Its full_proxy wrapper makes d…