From 4ea5763fb79ed89b3bdad455ebf3f33416a81624 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Fri, 14 Jan 2022 14:33:30 +0100 Subject: [PATCH] HID: uhid: Fix worker destroying device without any protection uhid has to run hid_add_device() from workqueue context while allowing parallel use of the userspace API (which is protected with ->devlock). But hid_add_device() can fail. Currently, that is handled by immediately destroying the associated HID device, without using ->devlock - but if there are concurrent requests from userspace, that's wrong and leads to NULL dereferences and/or memory corruption (via use-after-free). Fix it by leaving the HID device as-is in the worker. We can clean it up later, either in the UHID_DESTROY command handler or in the ->release() handler. Cc: stable@vger.kernel.org Fixes: 67f8ecc550b5 ("HID: uhid: fix timeout when probe races with IO") Signed-off-by: Jann Horn Signed-off-by: Jiri Kosina --- drivers/hid/uhid.c | 29 +++++++++++++++++++++++++---- 1 file changed, 25 insertions(+), 4 deletions(-) diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c index 8fe3efcb8327..fc06d8bb42e0 100644 --- a/drivers/hid/uhid.c +++ b/drivers/hid/uhid.c @@ -28,11 +28,22 @@ struct uhid_device { struct mutex devlock; + + /* This flag tracks whether the HID device is usable for commands from + * userspace. The flag is already set before hid_add_device(), which + * runs in workqueue context, to allow hid_add_device() to communicate + * with userspace. + * However, if hid_add_device() fails, the flag is cleared without + * holding devlock. + * We guarantee that if @running changes from true to false while you're + * holding @devlock, it's still fine to access @hid. + */ bool running; __u8 *rd_data; uint rd_size; + /* When this is NULL, userspace may use UHID_CREATE/UHID_CREATE2. */ struct hid_device *hid; struct uhid_event input_buf; @@ -63,9 +74,18 @@ static void uhid_device_add_worker(struct work_struct *work) if (ret) { hid_err(uhid->hid, "Cannot register HID device: error %d\n", ret); - hid_destroy_device(uhid->hid); - uhid->hid = NULL; + /* We used to call hid_destroy_device() here, but that's really + * messy to get right because we have to coordinate with + * concurrent writes from userspace that might be in the middle + * of using uhid->hid. + * Just leave uhid->hid as-is for now, and clean it up when + * userspace tries to close or reinitialize the uhid instance. + * + * However, we do have to clear the ->running flag and do a + * wakeup to make sure userspace knows that the device is gone. + */ uhid->running = false; + wake_up_interruptible(&uhid->report_wait); } } @@ -474,7 +494,7 @@ static int uhid_dev_create2(struct uhid_device *uhid, void *rd_data; int ret; - if (uhid->running) + if (uhid->hid) return -EALREADY; rd_size = ev->u.create2.rd_size; @@ -556,7 +576,7 @@ static int uhid_dev_create(struct uhid_device *uhid, static int uhid_dev_destroy(struct uhid_device *uhid) { - if (!uhid->running) + if (!uhid->hid) return -EINVAL; uhid->running = false; @@ -565,6 +585,7 @@ static int uhid_dev_destroy(struct uhid_device *uhid) cancel_work_sync(&uhid->worker); hid_destroy_device(uhid->hid); + uhid->hid = NULL; kfree(uhid->rd_data); return 0;