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Mon, 10 Aug 2026 05:12:14 -0700 (PDT) Received: from kali ([135.136.16.250]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4995e9f9424sm254883645e9.8.2026.08.10.05.12.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Aug 2026 05:12:14 -0700 (PDT) From: =?UTF-8?q?Miguel=20Pe=C3=B1aranda?= To: linux-usb@vger.kernel.org Cc: linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org Subject: [PATCH] usb: usbfs: fix use-after-free of usb_device in usbdev_release() Date: Mon, 10 Aug 2026 14:12:09 +0200 Message-ID: <20260810121209.795089-1-mig.penaranda07@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit usbdev_release() drops its reference to the struct usb_device before draining the list of completed async URBs, but that drain path reads back through the same object: free_async() calls dec_usb_memory_use_count() for any URB whose buffer came from the usbfs mmap() region, and its first statement is bus_to_hcd(ps->dev->bus). After a disconnect the usbfs reference can be the last one, in which case usb_put_dev() frees the device and the subsequent loop reads offset 80 of freed memory and uses the result as a struct usb_hcd *, which hcd_buffer_free_pages() then dereferences. This is reachable by an unprivileged process that has read/write access to a /dev/bus/usb node: mmap() the fd, submit one URB with a buffer inside the mapping, wait for the device to be unplugged, then munmap() and close(). It reproduces on every attempt rather than being a race, because a live MAP_SHARED vma holds a reference on the struct file, so usbdev_release() cannot run until the last vma is gone and the freeing branch of dec_usb_memory_use_count() is always taken. BUG: KASAN: slab-use-after-free in dec_usb_memory_use_count+0x3ae/0x410 Read of size 8 at addr ffff8880122ee050 by task poc/769 CPU: 1 UID: 1000 PID: 769 Comm: poc Tainted: G B 6.12.94 #3 Call Trace: dec_usb_memory_use_count+0x3ae/0x410 free_async+0x2aa/0x4f0 usbdev_release+0x375/0x460 __fput+0x3ea/0xb50 __x64_sys_close+0x86/0x100 Allocated by task 11: usb_alloc_dev+0x55/0xd90 hub_event+0x2524/0x43d0 Freed by task 769: kfree+0x121/0x360 device_release+0xd2/0x280 usb_put_dev+0x23/0x30 usbdev_release+0x2d8/0x460 Release the device reference after the drain loop instead. Nothing between the two points requires it to have been dropped. Fixes: f7d34b445abc ("USB: Add support for usbfs zerocopy.") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-5 Signed-off-by: Miguel Peñaranda --- drivers/usb/core/devio.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c index e191934..486ced7 100644 --- a/drivers/usb/core/devio.c +++ b/drivers/usb/core/devio.c @@ -1113,7 +1113,6 @@ static int usbdev_release(struct inode *inode, struct file *file) if (!ps->suspend_allowed) usb_autosuspend_device(dev); usb_unlock_device(dev); - usb_put_dev(dev); put_pid(ps->disc_pid); put_cred(ps->cred); @@ -1122,6 +1121,7 @@ static int usbdev_release(struct inode *inode, struct file *file) free_async(as); as = async_getcompleted(ps); } + usb_put_dev(dev); kfree(ps); return 0; -- 2.53.0