tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux
1
fork

Configure Feed

Select the types of activity you want to include in your feed.

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 <alexander.sverdlin@siemens.com>
Closes: https://lore.kernel.org/all/5d605f7fc99456804911403102a4fe999a14cc85.camel@siemens.com/
Tested-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Link: https://lore.kernel.org/r/20251117-gpio-cdev-get-file-v1-1-28a16b5985b8@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Bartosz Golaszewski d4cd0902 6a23ae0a

+7 -2
+7 -2
drivers/gpio/gpiolib-cdev.c
··· 2548 2548 container_of(nb, struct gpio_chardev_data, lineinfo_changed_nb); 2549 2549 struct lineinfo_changed_ctx *ctx; 2550 2550 struct gpio_desc *desc = data; 2551 + struct file *fp; 2551 2552 2552 2553 if (!test_bit(gpio_chip_hwgpio(desc), cdev->watched_lines)) 2554 + return NOTIFY_DONE; 2555 + 2556 + /* Keep the file descriptor alive for the duration of the notification. */ 2557 + fp = get_file_active(&cdev->fp); 2558 + if (!fp) 2559 + /* Chardev file descriptor was or is being released. */ 2553 2560 return NOTIFY_DONE; 2554 2561 2555 2562 /* ··· 2582 2575 /* Keep the GPIO device alive until we emit the event. */ 2583 2576 ctx->gdev = gpio_device_get(desc->gdev); 2584 2577 ctx->cdev = cdev; 2585 - /* Keep the file descriptor alive too. */ 2586 - get_file(ctx->cdev->fp); 2587 2578 2588 2579 INIT_WORK(&ctx->work, lineinfo_changed_func); 2589 2580 queue_work(ctx->gdev->line_state_wq, &ctx->work);