From 03f449b5de36a25fc5eba7dabf2b4494389bdb91 Mon Sep 17 00:00:00 2001 From: Yousef Alhouseen Date: Mon, 29 Jun 2026 17:29:47 +0200 Subject: [PATCH] HID: hiddev: keep state alive through disconnect unlock mutex_unlock() clears the mutex owner before taking its wait lock. A thread spinning in the final hiddev file release can acquire existancelock after hiddev_disconnect() clears the owner, then free hiddev before the disconnecting thread reaches the mutex wait lock. This causes a use-after-free in the mutex slow unlock path. Give the connection and each open file an explicit reference. Drop each reference only after its existancelock critical section has completed, so neither unlock path can free the mutex while the other is still using it. Fixes: 079034073faf ("HID: hiddev cleanup -- handle all error conditions properly") Reported-by: syzbot+563191a4939ddbfe73d4@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=563191a4939ddbfe73d4 Cc: stable@vger.kernel.org Signed-off-by: Yousef Alhouseen Link: https://syzkaller.appspot.com/bug?extid=563191a4939ddbfe73d4 Signed-off-by: Jiri Kosina --- drivers/hid/usbhid/hiddev.c | 37 +++++++++++++++++++------------------ include/linux/hiddev.h | 2 ++ 2 files changed, 21 insertions(+), 18 deletions(-) diff --git a/drivers/hid/usbhid/hiddev.c b/drivers/hid/usbhid/hiddev.c index 6378801b22c6..21396481995b 100644 --- a/drivers/hid/usbhid/hiddev.c +++ b/drivers/hid/usbhid/hiddev.c @@ -46,6 +46,12 @@ struct hiddev_list { struct mutex thread_lock; }; +static void hiddev_put(struct hiddev *hiddev) +{ + if (refcount_dec_and_test(&hiddev->refcount)) + kfree(hiddev); +} + /* * Find a report, given the report's type and ID. The ID can be specified * indirectly by REPORT_ID_FIRST (which returns the first report of the given @@ -216,26 +222,21 @@ static int hiddev_fasync(int fd, struct file *file, int on) static int hiddev_release(struct inode * inode, struct file * file) { struct hiddev_list *list = file->private_data; + struct hiddev *hiddev = list->hiddev; unsigned long flags; - spin_lock_irqsave(&list->hiddev->list_lock, flags); + spin_lock_irqsave(&hiddev->list_lock, flags); list_del(&list->node); - spin_unlock_irqrestore(&list->hiddev->list_lock, flags); + spin_unlock_irqrestore(&hiddev->list_lock, flags); - mutex_lock(&list->hiddev->existancelock); - if (!--list->hiddev->open) { - if (list->hiddev->exist) { - hid_hw_close(list->hiddev->hid); - hid_hw_power(list->hiddev->hid, PM_HINT_NORMAL); - } else { - mutex_unlock(&list->hiddev->existancelock); - kfree(list->hiddev); - vfree(list); - return 0; - } + mutex_lock(&hiddev->existancelock); + if (!--hiddev->open && hiddev->exist) { + hid_hw_close(hiddev->hid); + hid_hw_power(hiddev->hid, PM_HINT_NORMAL); } - mutex_unlock(&list->hiddev->existancelock); + mutex_unlock(&hiddev->existancelock); + hiddev_put(hiddev); vfree(list); return 0; @@ -270,6 +271,7 @@ static int __hiddev_open(struct hiddev *hiddev, struct file *file) spin_unlock_irq(&hiddev->list_lock); file->private_data = list; + refcount_inc(&hiddev->refcount); return 0; @@ -897,6 +899,7 @@ int hiddev_connect(struct hid_device *hid, unsigned int force) INIT_LIST_HEAD(&hiddev->list); spin_lock_init(&hiddev->list_lock); mutex_init(&hiddev->existancelock); + refcount_set(&hiddev->refcount, 1); hid->hiddev = hiddev; hiddev->hid = hid; hiddev->exist = 1; @@ -937,9 +940,7 @@ void hiddev_disconnect(struct hid_device *hid) if (hiddev->open) { hid_hw_close(hiddev->hid); wake_up_interruptible(&hiddev->wait); - mutex_unlock(&hiddev->existancelock); - } else { - mutex_unlock(&hiddev->existancelock); - kfree(hiddev); } + mutex_unlock(&hiddev->existancelock); + hiddev_put(hiddev); } diff --git a/include/linux/hiddev.h b/include/linux/hiddev.h index 2164c03d2c72..8e9f8a33e359 100644 --- a/include/linux/hiddev.h +++ b/include/linux/hiddev.h @@ -13,6 +13,7 @@ #ifndef _HIDDEV_H #define _HIDDEV_H +#include #include @@ -24,6 +25,7 @@ struct hiddev { int minor; int exist; int open; + refcount_t refcount; struct mutex existancelock; wait_queue_head_t wait; struct hid_device *hid;