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([121.185.186.233]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2466885efd4sm20931775ad.69.2025.08.23.05.04.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 23 Aug 2025 05:04:04 -0700 (PDT) From: Jeongjun Park To: mchehab@kernel.org, khoroshilov@ispras.ru Cc: linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, syzbot+47321e8fd5a4c84088db@syzkaller.appspotmail.com, Jeongjun Park Subject: [PATCH v2] media: as102: fix to not free memory after the device is registered in as102_usb_probe() Date: Sat, 23 Aug 2025 21:02:57 +0900 Message-Id: <20250823120257.1176990-1-aha310510@gmail.com> X-Mailer: git-send-email 2.34.1 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" In as102_usb driver, the following race condition occurs: ``` CPU0 CPU1 as102_usb_probe() kzalloc(); // alloc as102_dev_t .... usb_register_dev(); open("/path/to/dev"); // open as102 dev .... usb_deregister_dev(); .... kfree(); // free as102_dev_t .... close(fd); as102_release() // UAF!! as102_usb_release() kfree(); // DFB!! ``` When a USB character device registered with usb_register_dev() is later unregistered (via usb_deregister_dev() or disconnect), the device node is removed so new open() calls fail. However, file descriptors that are already open do not go away immediately: they remain valid until the last reference is dropped and the driver's .release() is invoked. In as102, as102_usb_probe() calls usb_register_dev() and then, on an error path, does usb_deregister_dev() and frees as102_dev_t right away. If userspace raced a successful open() before the deregistration, that open FD will later hit as102_release() --> as102_usb_release() and access or free as102_dev_t again, occur a race to use-after-free and double-free vuln. The fix is to never kfree(as102_dev_t) directly once usb_register_dev() has succeeded. After deregistration, defer freeing memory to .release(). In other words, let release() perform the last kfree when the final open FD is closed. Cc: Reported-by: syzbot+47321e8fd5a4c84088db@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D47321e8fd5a4c84088db Fixes: cd19f7d3e39b ("[media] as102: fix leaks at failure paths in as102_us= b_probe()") Signed-off-by: Jeongjun Park --- v2: Fix incorrect patch description style and CC stable mailing list - Link to v1: https://lore.kernel.org/all/20250822143539.1157329-1-aha31051= 0@gmail.com/ --- drivers/media/usb/as102/as102_usb_drv.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/media/usb/as102/as102_usb_drv.c b/drivers/media/usb/as= 102/as102_usb_drv.c index e0ef66a522e2..abde5666b2ee 100644 --- a/drivers/media/usb/as102/as102_usb_drv.c +++ b/drivers/media/usb/as102/as102_usb_drv.c @@ -404,6 +404,7 @@ static int as102_usb_probe(struct usb_interface *intf, as102_free_usb_stream_buffer(as102_dev); failed_stream: usb_deregister_dev(intf, &as102_usb_class_driver); + return ret; failed: usb_put_dev(as102_dev->bus_adap.usb_dev); usb_set_intfdata(intf, NULL); --