From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 0032A3F4130 for ; Thu, 9 Jul 2026 10:30:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783593013; cv=none; b=GixmWNmX2cQ6bufELQP5Uq0+e4FjVtTkmpQYxPasiYwvc6PutovlIOGuztZdUnRaalpOPtngYPIHuaS2VttoDcdJOK/2GwJGXaE97Sb5gUVlpOGHRBRWTjvo+XHjKI5iHoEXFJAuGplIj25ernN9gJLQ1MSt49sw3eJfe9nOjik= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783593013; c=relaxed/simple; bh=wDwgK4DmfpyN3qUc9Q7k2BsFZ0Uk72G4GD3ygs2wyX4=; h=From:Subject:To:Cc:In-Reply-To:References:Content-Type:Date: Message-Id; b=GIK2GROF2B1p/XuNeOl01CYFM0cW10U8J2hQjO/gU2tMgLDsh9YqWjGMCwRXDkbvgWyGBDb32nt8LnsiCwbgjmQedLxAWCL6W/DTyT3UMBVMDUaURe2F8UTL5TGJCRtEV9InEqe9K8f072KP8pXVlJLfCCPXggFDktEe1vedw08= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bPXya8ka; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bPXya8ka" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 60FE51F000E9; Thu, 9 Jul 2026 10:30:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783593011; bh=otLjqzIoJw41IlWu0vwoLX52jhne64d2NrWLno9ANqc=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=bPXya8ka9TJ8gaZ4okfTyNuo1Ivew+Ur1JNI+E1M5TjNnr8p2E+Ffj+2ylQuy6U6g bdxZ7xXvWmUyEqKaobf/sCyk7Sqhq0D/qS7nWVDVoHgt3cSv2bR2YfthqEWZDcgdCM bD79nx0Nqsfj4mnWZCYuL1RwbOjjdh63jHRfftTFW0rh/Amgh6gYiltBl/uWvFSX5b 3Z1+BEm/X+dvWCDY5XTnvcTlxxK0MpSkaIT2SE9aD+X211miqaTjD/zUhOYXyNcn5D zdWmzgGJJb5NuX0M8Z5MPiZJxI39SklncubMqKFUBG8LwNbVmRHrww/OrgacSArSAa qFbRWSCbNEZ3Q== From: sashiko-bot@kernel.org Subject: Re: [PATCH] leds: class: disable sysfs before unregistering LED devices Reply-To: sashiko-reviews@lists.linux.dev To: "David Lee" Cc: linux-leds@vger.kernel.org, lee@kernel.org In-Reply-To: <20260709101210.104975-1-david.lee@trailofbits.com> References: <20260709101210.104975-1-david.lee@trailofbits.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Thu, 09 Jul 2026 10:30:10 +0000 Message-Id: <20260709103011.60FE51F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: linux-leds@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Thank you for your contribution! Sashiko AI review found 4 potential issue(= s) to consider: New issues: - [High] Reusing `LED_SYSFS_DISABLE` for unregistration teardown conflicts = with V4L2 flash, which can clear the flag during unregistration and bypass = the patch's protection. Pre-existing issues: - [High] This problem wasn't introduced by this patch, but missing the `led= _sysfs_is_disabled()` check in `multi_intensity_store()` bypasses the patch= 's newly introduced teardown protection, allowing the use-after-free to sti= ll occur for multicolor LEDs. - [High] This problem wasn't introduced by this patch, but concurrent `led_= trigger_register` can attach a trigger to an unregistering LED device whose= embedded `dev` structure has already been freed, leading to a Use-After-Fr= ee. - [High] This problem wasn't introduced by this patch, but LED triggers hav= e a Use-After-Free race condition where their sysfs attributes can execute = concurrently with or after trigger deactivation. -- --- Patch [1]: [PATCH] leds: class: disable sysfs before unregistering LED = devices --- commit a26d864d321effb464ac1db24d6210a72a4d07d3 Author: David Lee Subject: leds: class: disable sysfs before unregistering LED devices This commit attempts to fix a lifetime race during LED unregistration by locking led_access and setting LED_SYSFS_DISABLE early in led_classdev_unregister(). This blocks sysfs writers from accessing the embedded struct led_classdev while it is being torn down. > diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c > index 6a8ea94834fa3..a6c2468c0da1e 100644 > --- a/drivers/leds/led-class.c > +++ b/drivers/leds/led-class.c > @@ -435,6 +435,9 @@ void led_classdev_unregister(struct led_classdev *led= _cdev) > if (IS_ERR_OR_NULL(led_cdev->dev)) > return; > =20 > + mutex_lock(&led_cdev->led_access); > + led_sysfs_disable(led_cdev); > + [Severity: High] Does overloading LED_SYSFS_DISABLE for unregistration conflict with V4L2 flash devices? If a user closes the V4L2 subdevice file concurrently during driver removal, v4l2_flash_close() actively clears this flag: drivers/media/v4l2-core/v4l2-flash-led-class.c:v4l2_flash_close() { ... led_sysfs_enable(led_cdev); mutex_unlock(&led_cdev->led_access); } Could this allow a blocked sysfs writer to acquire led_access after unregister unlocks it, incorrectly see sysfs as enabled, and schedule work on an unregistering or freed device? [Severity: High] This isn't a bug introduced by this patch, but does the lack of a led_sysfs_is_disabled() check in multi_intensity_store() bypass this newly added teardown protection? If a concurrent sysfs write to multi_intensity blocks on led_access, and acquires it after unregister unlocks it: drivers/leds/led-class-multicolor.c:multi_intensity_store() { ... mutex_lock(&led_cdev->led_access); for (i =3D 0; i < mcled_cdev->num_colors; i++) { ... } Because it immediately proceeds without checking if sysfs is disabled, could it call led_set_brightness() and schedule new work after unregister has already flushed work queues, leading to a use-after-free? > #ifdef CONFIG_LEDS_TRIGGERS > down_write(&led_cdev->trigger_lock); > if (led_cdev->trigger) > led_trigger_set(led_cdev, NULL); > up_write(&led_cdev->trigger_lock); > #endif [Severity: High] This isn't a bug introduced by this patch, but is there a use-after-free race condition when clearing the trigger here? In led_trigger_set(), the deactivate callback is executed before the sysfs groups are removed: drivers/leds/led-triggers.c:led_trigger_set() { ... if (led_cdev->trigger->deactivate) led_cdev->trigger->deactivate(led_cdev); device_remove_groups(led_cdev->dev, led_cdev->trigger->groups); ... } Since sysfs operations for triggers (like transient_activate_store()) do not acquire led_access, could a sysfs write that is preempted resume after deactivate() frees the private data, modifying freed memory before device_remove_groups() can prevent it? [ ... ] > @@ -455,6 +458,8 @@ void led_classdev_unregister(struct led_classdev *led= _cdev) > if (led_cdev->flags & LED_BRIGHT_HW_CHANGED) > led_remove_brightness_hw_changed(led_cdev); > =20 > + mutex_unlock(&led_cdev->led_access); > + > device_unregister(led_cdev->dev); > =20 > down_write(&leds_list_lock); > list_del(&led_cdev->node); > up_write(&leds_list_lock); [Severity: High] This isn't a bug introduced by this patch, but does unregistering the device before removing the LED from the global leds_list leave a dangling pointer? If device_unregister() drops the final reference and frees the device structure, could a concurrent led_trigger_register() iterating over leds_list match this unregistering LED? drivers/leds/led-triggers.c:led_trigger_set() { ... ret =3D device_add_groups(led_cdev->dev, trig->groups); if (ret) { ... } Could this lead to led_trigger_set() dereferencing the already-freed led_cdev->dev when attempting to attach the trigger's sysfs groups? --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20260709101210.1049= 75-1-david.lee@trailofbits.com?part=3D1