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

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 debugfs_remove_recursive() drain any in-flight ->write
before it returns.

The use-after-free is confirmed under KASAN with a minimal reproducer of
the same debugfs_create_file_unsafe() plus devm_kzalloc() pattern
(available on request); it produces a slab-use-after-free write in the
handler.

Fixes: 7828b7bbbf20 ("gpio: add sloppy logic analyzer using polling")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4.8
Signed-off-by: Cengiz Can <cengiz.can@canonical.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://patch.msgid.link/20260730220258.358169-2-cengiz.can@canonical.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>