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([2405:201:682f:389d:d95a:1e5e:256b:2761]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a10e079284sm71689365ad.33.2025.12.16.21.49.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Dec 2025 21:49:18 -0800 (PST) From: Deepanshu Kartikey To: krzk@kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Deepanshu Kartikey , syzbot+4ef89409a235d804c6c2@syzkaller.appspotmail.com Subject: [PATCH] net: nfc: fix deadlock between nfc_unregister_device and rfkill_fop_write Date: Wed, 17 Dec 2025 11:19:08 +0530 Message-ID: <20251217054908.178907-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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. To ensure safety, set shutting_down flag first and store rfkill pointer in a local variable before releasing the lock. The shutting_down flag ensures that nfc_dev_down() and nfc_dev_up() will bail out early if called during device unregistration. Reported-by: syzbot+4ef89409a235d804c6c2@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D4ef89409a235d804c6c2 Signed-off-by: Deepanshu Kartikey --- net/nfc/core.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/net/nfc/core.c b/net/nfc/core.c index ae1c842f9c64..201d2b95432b 100644 --- a/net/nfc/core.c +++ b/net/nfc/core.c @@ -1154,7 +1154,7 @@ EXPORT_SYMBOL(nfc_register_device); void nfc_unregister_device(struct nfc_dev *dev) { int rc; - + struct rfkill *rfk =3D NULL; pr_debug("dev_name=3D%s\n", dev_name(&dev->dev)); =20 rc =3D nfc_genl_device_removed(dev); @@ -1164,13 +1164,17 @@ void nfc_unregister_device(struct nfc_dev *dev) =20 device_lock(&dev->dev); if (dev->rfkill) { - rfkill_unregister(dev->rfkill); - rfkill_destroy(dev->rfkill); + rfk =3D dev->rfkill; dev->rfkill =3D NULL; } dev->shutting_down =3D true; device_unlock(&dev->dev); =20 + 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); --=20 2.43.0