From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A6F193D522C; Wed, 8 Apr 2026 18:39:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775673562; cv=none; b=XJZVhx2oefW7xOvrOSo3ac8WMPhm0Tn8FWoqsIsQSPTc91MUyz/JGqROV9ePvhbYn2r4djhbP0U9x2QUMshrZ5+Rm2dG9APTzYoDV/QPgfL+zXcsgQfwsfqmXHjFJDhuF9ptb1fk3BTOzU778+IhZqo87FWC8CsAY+5vO8fsyz4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775673562; c=relaxed/simple; bh=Gk/KXRGfAd/nFV5dDO4cR62rBiWDBd8Z8ODEujsNteU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=YvWt2Wk+yXlrfaiLFeNm7sMzGPTTmxz2BGeyUbj51C/1S7S1Zhl1zxpgK3NizhoEvsJF5PjN1VEv+tk0cc4xdtO4brRrKblvLYnUtwa18gK5SiIt2XtaaPd5HJLRltVdoPUZ+/ARqFdzWQ7NeQ+ihzmLEWVEYY354ifT+ZW6KJo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=pBP83YwJ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="pBP83YwJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3D183C19421; Wed, 8 Apr 2026 18:39:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1775673562; bh=Gk/KXRGfAd/nFV5dDO4cR62rBiWDBd8Z8ODEujsNteU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pBP83YwJzuUTZWpYOMgzzSL/l8X2kIRJuqyqVXZqxQaM90nFAVXkNg4PBU2nzUxcc sEOT+tA4y+swX95V19s2s4WVkhZsU5U81/2RRu1Dsyy/yA0YfLR5PBsHsSjlL5MlYL ZJuSG4lPeyT/ZDnsbZKG7jdSw+OElIlWvMg2CO4E= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, stable , Alan Stern , Jimmy Hu Subject: [PATCH 6.18 254/277] usb: gadget: uvc: fix NULL pointer dereference during unbind race Date: Wed, 8 Apr 2026 20:03:59 +0200 Message-ID: <20260408175943.342406315@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260408175933.836769063@linuxfoundation.org> References: <20260408175933.836769063@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jimmy Hu commit eba2936bbe6b752a31725a9eb5c674ecbf21ee7d upstream. Commit b81ac4395bbe ("usb: gadget: uvc: allow for application to cleanly shutdown") introduced two stages of synchronization waits totaling 1500ms in uvc_function_unbind() to prevent several types of kernel panics. However, this timing-based approach is insufficient during power management (PM) transitions. When the PM subsystem starts freezing user space processes, the wait_event_interruptible_timeout() is aborted early, which allows the unbind thread to proceed and nullify the gadget pointer (cdev->gadget = NULL): [ 814.123447][ T947] configfs-gadget.g1 gadget.0: uvc: uvc_function_unbind() [ 814.178583][ T3173] PM: suspend entry (deep) [ 814.192487][ T3173] Freezing user space processes [ 814.197668][ T947] configfs-gadget.g1 gadget.0: uvc: uvc_function_unbind no clean disconnect, wait for release When the PM subsystem resumes or aborts the suspend and tasks are restarted, the V4L2 release path is executed and attempts to access the already nullified gadget pointer, triggering a kernel panic: [ 814.292597][ C0] PM: pm_system_irq_wakeup: 479 triggered dhdpcie_host_wake [ 814.386727][ T3173] Restarting tasks ... [ 814.403522][ T4558] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000030 [ 814.404021][ T4558] pc : usb_gadget_deactivate+0x14/0xf4 [ 814.404031][ T4558] lr : usb_function_deactivate+0x54/0x94 [ 814.404078][ T4558] Call trace: [ 814.404080][ T4558] usb_gadget_deactivate+0x14/0xf4 [ 814.404083][ T4558] usb_function_deactivate+0x54/0x94 [ 814.404087][ T4558] uvc_function_disconnect+0x1c/0x5c [ 814.404092][ T4558] uvc_v4l2_release+0x44/0xac [ 814.404095][ T4558] v4l2_release+0xcc/0x130 Address the race condition and NULL pointer dereference by: 1. State Synchronization (flag + mutex) Introduce a 'func_unbound' flag in struct uvc_device. This allows uvc_function_disconnect() to safely skip accessing the nullified cdev->gadget pointer. As suggested by Alan Stern, this flag is protected by a new mutex (uvc->lock) to ensure proper memory ordering and prevent instruction reordering or speculative loads. This mutex is also used to protect 'func_connected' for consistent state management. 2. Explicit Synchronization (completion) Use a completion to synchronize uvc_function_unbind() with the uvc_vdev_release() callback. This prevents Use-After-Free (UAF) by ensuring struct uvc_device is freed after all video device resources are released. Fixes: b81ac4395bbe ("usb: gadget: uvc: allow for application to cleanly shutdown") Cc: stable Suggested-by: Alan Stern Signed-off-by: Jimmy Hu Link: https://patch.msgid.link/20260320065427.1374555-1-hhhuuu@google.com Signed-off-by: Greg Kroah-Hartman Signed-off-by: Greg Kroah-Hartman --- drivers/usb/gadget/function/f_uvc.c | 39 ++++++++++++++++++++++++++++++--- drivers/usb/gadget/function/uvc.h | 3 ++ drivers/usb/gadget/function/uvc_v4l2.c | 5 +++- 3 files changed, 43 insertions(+), 4 deletions(-) --- a/drivers/usb/gadget/function/f_uvc.c +++ b/drivers/usb/gadget/function/f_uvc.c @@ -413,6 +413,12 @@ uvc_function_disconnect(struct uvc_devic { int ret; + guard(mutex)(&uvc->lock); + if (uvc->func_unbound) { + dev_dbg(&uvc->vdev.dev, "skipping function deactivate (unbound)\n"); + return; + } + if ((ret = usb_function_deactivate(&uvc->func)) < 0) uvcg_info(&uvc->func, "UVC disconnect failed with %d\n", ret); } @@ -431,6 +437,15 @@ static ssize_t function_name_show(struct static DEVICE_ATTR_RO(function_name); +static void uvc_vdev_release(struct video_device *vdev) +{ + struct uvc_device *uvc = video_get_drvdata(vdev); + + /* Signal uvc_function_unbind() that the video device has been released */ + if (uvc->vdev_release_done) + complete(uvc->vdev_release_done); +} + static int uvc_register_video(struct uvc_device *uvc) { @@ -443,7 +458,7 @@ uvc_register_video(struct uvc_device *uv uvc->vdev.v4l2_dev->dev = &cdev->gadget->dev; uvc->vdev.fops = &uvc_v4l2_fops; uvc->vdev.ioctl_ops = &uvc_v4l2_ioctl_ops; - uvc->vdev.release = video_device_release_empty; + uvc->vdev.release = uvc_vdev_release; uvc->vdev.vfl_dir = VFL_DIR_TX; uvc->vdev.lock = &uvc->video.mutex; uvc->vdev.device_caps = V4L2_CAP_VIDEO_OUTPUT | V4L2_CAP_STREAMING; @@ -659,6 +674,8 @@ uvc_function_bind(struct usb_configurati int ret = -EINVAL; uvcg_info(f, "%s()\n", __func__); + scoped_guard(mutex, &uvc->lock) + uvc->func_unbound = false; opts = fi_to_f_uvc_opts(f->fi); /* Sanity check the streaming endpoint module parameters. */ @@ -988,12 +1005,19 @@ static void uvc_free(struct usb_function static void uvc_function_unbind(struct usb_configuration *c, struct usb_function *f) { + DECLARE_COMPLETION_ONSTACK(vdev_release_done); struct usb_composite_dev *cdev = c->cdev; struct uvc_device *uvc = to_uvc(f); struct uvc_video *video = &uvc->video; long wait_ret = 1; + bool connected; uvcg_info(f, "%s()\n", __func__); + scoped_guard(mutex, &uvc->lock) { + uvc->func_unbound = true; + uvc->vdev_release_done = &vdev_release_done; + connected = uvc->func_connected; + } kthread_cancel_work_sync(&video->hw_submit); @@ -1006,7 +1030,7 @@ static void uvc_function_unbind(struct u * though the video device removal uevent. Allow some time for the * application to close out before things get deleted. */ - if (uvc->func_connected) { + if (connected) { uvcg_dbg(f, "waiting for clean disconnect\n"); wait_ret = wait_event_interruptible_timeout(uvc->func_connected_queue, uvc->func_connected == false, msecs_to_jiffies(500)); @@ -1017,7 +1041,10 @@ static void uvc_function_unbind(struct u video_unregister_device(&uvc->vdev); v4l2_device_unregister(&uvc->v4l2_dev); - if (uvc->func_connected) { + scoped_guard(mutex, &uvc->lock) + connected = uvc->func_connected; + + if (connected) { /* * Wait for the release to occur to ensure there are no longer any * pending operations that may cause panics when resources are cleaned @@ -1029,6 +1056,10 @@ static void uvc_function_unbind(struct u uvcg_dbg(f, "done waiting for release with ret: %ld\n", wait_ret); } + /* Wait for the video device to be released */ + wait_for_completion(&vdev_release_done); + uvc->vdev_release_done = NULL; + usb_ep_free_request(cdev->gadget->ep0, uvc->control_req); kfree(uvc->control_buf); @@ -1047,6 +1078,8 @@ static struct usb_function *uvc_alloc(st return ERR_PTR(-ENOMEM); mutex_init(&uvc->video.mutex); + mutex_init(&uvc->lock); + uvc->func_unbound = true; uvc->state = UVC_STATE_DISCONNECTED; init_waitqueue_head(&uvc->func_connected_queue); opts = fi_to_f_uvc_opts(fi); --- a/drivers/usb/gadget/function/uvc.h +++ b/drivers/usb/gadget/function/uvc.h @@ -155,6 +155,9 @@ struct uvc_device { enum uvc_state state; struct usb_function func; struct uvc_video video; + struct completion *vdev_release_done; + struct mutex lock; /* protects func_unbound and func_connected */ + bool func_unbound; bool func_connected; wait_queue_head_t func_connected_queue; --- a/drivers/usb/gadget/function/uvc_v4l2.c +++ b/drivers/usb/gadget/function/uvc_v4l2.c @@ -574,6 +574,8 @@ uvc_v4l2_subscribe_event(struct v4l2_fh if (sub->type < UVC_EVENT_FIRST || sub->type > UVC_EVENT_LAST) return -EINVAL; + guard(mutex)(&uvc->lock); + if (sub->type == UVC_EVENT_SETUP && uvc->func_connected) return -EBUSY; @@ -595,7 +597,8 @@ static void uvc_v4l2_disable(struct uvc_ uvc_function_disconnect(uvc); uvcg_video_disable(&uvc->video); uvcg_free_buffers(&uvc->video.queue); - uvc->func_connected = false; + scoped_guard(mutex, &uvc->lock) + uvc->func_connected = false; wake_up_interruptible(&uvc->func_connected_queue); }