From: Cengiz Can Date: Thu, 30 Jul 2026 22:02:57 +0000 (+0300) Subject: gpio: sloppy-logic-analyzer: fix use-after-free via debugfs trigger on unbind X-Git-Tag: v7.2~29^2 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=44f3468a0aef1aabdad551898ab7cfa2a9d20e99;p=thirdparty%2Fkernel%2Flinux.git 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 Reviewed-by: Wolfram Sang Link: https://patch.msgid.link/20260730220258.358169-2-cengiz.can@canonical.com Signed-off-by: Bartosz Golaszewski --- diff --git a/drivers/gpio/gpio-sloppy-logic-analyzer.c b/drivers/gpio/gpio-sloppy-logic-analyzer.c index aa23b5779802..2f9a1f0384ad 100644 --- a/drivers/gpio/gpio-sloppy-logic-analyzer.c +++ b/drivers/gpio/gpio-sloppy-logic-analyzer.c @@ -300,7 +300,7 @@ static int gpio_la_poll_probe(struct platform_device *pdev) debugfs_create_ulong("delay_ns_acquisition", 0400, priv->debug_dir, &priv->acq_delay); debugfs_create_file_unsafe("buf_size", 0600, priv->debug_dir, priv, &fops_buf_size); debugfs_create_file_unsafe("capture", 0200, priv->debug_dir, priv, &fops_capture); - debugfs_create_file_unsafe("trigger", 0200, priv->debug_dir, priv, &fops_trigger); + debugfs_create_file("trigger", 0200, priv->debug_dir, priv, &fops_trigger); return 0; }