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[2a02:3100:aeaf:bd01:78a0:2a2d:507f:c97c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4955370d78csm114492445e9.12.2026.07.19.15.10.44 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sun, 19 Jul 2026 15:10:45 -0700 (PDT) From: Karl Mehltretter To: Greg Kroah-Hartman , Jiri Slaby Cc: Karl Mehltretter , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH v2 3/4] tty: don't oops in tty_unregister_device() when no cdev is registered Date: Mon, 20 Jul 2026 00:10:13 +0200 Message-Id: <20260719221014.44354-4-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20260719221014.44354-1-kmehltretter@gmail.com> References: <20260719221014.44354-1-kmehltretter@gmail.com> Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit serial_core_add_one_port() keeps a uart_port when tty device registration fails so setserial can still use it. It marks the port UPF_DEAD and returns success. Removing the port later reaches tty_unregister_device(), which unconditionally passes driver->cdevs[index] to cdev_del(). The slot does not always contain a live cdev. A serdev registration error other than -ENODEV returns before tty_register_device_attr(), leaving the slot NULL. If cdev_add() fails, tty_cdev_add() drops the cdev reference but leaves the slot pointing at freed memory. The later cdev_del() is therefore a NULL dereference or use-after-free. The NULL path was reproduced with failslab during UART bind on qemu's mcimx6ul-evk and raspi1ap boards: Unhandled fault: page domain fault (0x01b) at 0x00000038 PC is at cdev_del+0x14/0x34 Clear the slot after cdev_add() fails and only call cdev_del() when it is non-NULL. This makes a non-NULL slot mean that a live cdev is registered. Fixes: c1a752ba2d6b ("tty: don't leak cdev in tty_cdev_add()") Fixes: 8cde11b2baa1 ("tty/serdev: add serdev registration interface") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-fable-5 Signed-off-by: Karl Mehltretter --- drivers/tty/tty_io.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 6b283fd03ff8..4889076b975f 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -3167,8 +3167,10 @@ static int tty_cdev_add(struct tty_driver *driver, dev_t dev, driver->cdevs[index]->ops = &tty_fops; driver->cdevs[index]->owner = driver->owner; err = cdev_add(driver->cdevs[index], dev, count); - if (err) + if (err) { kobject_put(&driver->cdevs[index]->kobj); + driver->cdevs[index] = NULL; + } return err; } @@ -3305,7 +3307,7 @@ EXPORT_SYMBOL_GPL(tty_register_device_attr); void tty_unregister_device(struct tty_driver *driver, unsigned index) { device_destroy(&tty_class, MKDEV(driver->major, driver->minor_start) + index); - if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC)) { + if (!(driver->flags & TTY_DRIVER_DYNAMIC_ALLOC) && driver->cdevs[index]) { cdev_del(driver->cdevs[index]); driver->cdevs[index] = NULL; } -- 2.53.0