From d4cd0902c156b2ca60fdda8cd8b5bcb4b0e9ed64 Mon Sep 17 00:00:00 2001 From: Bartosz Golaszewski Date: Mon, 17 Nov 2025 16:08:42 +0100 Subject: [PATCH] gpio: cdev: make sure the cdev fd is still active before emitting events With the final call to fput() on a file descriptor, the release action may be deferred and scheduled on a work queue. The reference count of that descriptor is still zero and it must not be used. It's possible that a GPIO change, we want to notify the user-space about, happens AFTER the reference count on the file descriptor associated with the character device went down to zero but BEFORE the .release() callback was called from the workqueue and so BEFORE we unregistered from the notifier. Using the regular get_file() routine in this situation triggers the following warning: struct file::f_count incremented from zero; use-after-free condition present! So use the get_file_active() variant that will return NULL on file descriptors that have been or are being released. Fixes: 40b7c49950bd ("gpio: cdev: put emitting the line state events on a workqueue") Reported-by: Alexander Sverdlin Closes: https://lore.kernel.org/all/5d605f7fc99456804911403102a4fe999a14cc85.camel@siemens.com/ Tested-by: Alexander Sverdlin Link: https://lore.kernel.org/r/20251117-gpio-cdev-get-file-v1-1-28a16b5985b8@linaro.org Signed-off-by: Bartosz Golaszewski --- drivers/gpio/gpiolib-cdev.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c index 175836467f21..d8d93059ac04 100644 --- a/drivers/gpio/gpiolib-cdev.c +++ b/drivers/gpio/gpiolib-cdev.c @@ -2548,10 +2548,17 @@ static int lineinfo_changed_notify(struct notifier_block *nb, container_of(nb, struct gpio_chardev_data, lineinfo_changed_nb); struct lineinfo_changed_ctx *ctx; struct gpio_desc *desc = data; + struct file *fp; if (!test_bit(gpio_chip_hwgpio(desc), cdev->watched_lines)) return NOTIFY_DONE; + /* Keep the file descriptor alive for the duration of the notification. */ + fp = get_file_active(&cdev->fp); + if (!fp) + /* Chardev file descriptor was or is being released. */ + return NOTIFY_DONE; + /* * If this is called from atomic context (for instance: with a spinlock * taken by the atomic notifier chain), any sleeping calls must be done @@ -2575,8 +2582,6 @@ static int lineinfo_changed_notify(struct notifier_block *nb, /* Keep the GPIO device alive until we emit the event. */ ctx->gdev = gpio_device_get(desc->gdev); ctx->cdev = cdev; - /* Keep the file descriptor alive too. */ - get_file(ctx->cdev->fp); INIT_WORK(&ctx->work, lineinfo_changed_func); queue_work(ctx->gdev->line_state_wq, &ctx->work); -- 2.47.3