A deadlock can occur between nfc_unregister_device() and rfkill_fop_write() due to lock ordering inversion between device_lock and rfkill_global_mutex.

The problematic lock order is:

Thread A (rfkill_fop_write): rfkill_fop_write() mutex_lock(&rfkill_global_mutex) rfkill_set_block() nfc_rfkill_set_block() nfc_dev_down() device_lock(&dev->dev) <- waits for device_lock

Thread B (nfc_unregister_device): nfc_unregister_device() device_lock(&dev->dev) rfkill_unregister() mutex_lock(&rfkill_global_mutex) <- waits for rfkill_global_mutex

This creates a classic ABBA deadlock scenario.

Fix this by moving rfkill_unregister() and rfkill_destroy() outside the device_lock critical section. Store the rfkill pointer in a local variable before releasing the lock, then call rfkill_unregister() after releasing device_lock.

This change is safe because rfkill_fop_write() holds rfkill_global_mutex while calling the rfkill callbacks, and rfkill_unregister() also acquires rfkill_global_mutex before cleanup. Therefore, rfkill_unregister() will wait for any ongoing callback to complete before proceeding, and device_del() is only called after rfkill_unregister() returns, preventing any use-after-free.

The similar lock ordering in nfc_register_device() (device_lock -> rfkill_global_mutex via rfkill_register) is safe because during registration the device is not yet in rfkill_list, so no concurrent rfkill operations can occur on this device.

Fixes: 3e3b5dfcd16a ("NFC: reorder the logic in nfc_{un,}register_device") Cc: stable@vger.kernel.org Reported-by: syzbot+4ef89409a235d804c6c2@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=4ef89409a235d804c6c2 Link: https://lore.kernel.org/all/20251217054908.178907-1-kartikey406@gmail.com/T/ [v1] Signed-off-by: Deepanshu Kartikey kartikey406@gmail.com --- v2: - Added explanation of why UAF is not possible - Added explanation of why nfc_register_device() is safe - Added Fixes and Cc: stable tags - Fixed blank line after variable declaration (kept it) --- net/nfc/core.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/nfc/core.c b/net/nfc/core.c index ae1c842f9c64..82f023f37754 100644 --- a/net/nfc/core.c +++ b/net/nfc/core.c @@ -1154,6 +1154,7 @@ EXPORT_SYMBOL(nfc_register_device); void nfc_unregister_device(struct nfc_dev *dev) { int rc; + struct rfkill *rfk = NULL;

pr_debug("dev_name=%s\n", dev_name(&dev->dev));

@@ -1164,13 +1165,17 @@ void nfc_unregister_device(struct nfc_dev *dev)

device_lock(&dev->dev); if (dev->rfkill) { - rfkill_unregister(dev->rfkill); - rfkill_destroy(dev->rfkill); + rfk = dev->rfkill; dev->rfkill = NULL; } dev->shutting_down = true; device_unlock(&dev->dev);

+ if (rfk) { + rfkill_unregister(rfk); + rfkill_destroy(rfk); + } + if (dev->ops->check_presence) { timer_delete_sync(&dev->check_pres_timer); cancel_work_sync(&dev->check_pres_work);