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 4CBDB3FDBE5; Tue, 7 Jul 2026 12:11:13 +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=1783426274; cv=none; b=ny4UNy4nEmi6WcXu0pKE0g6zFF8oDvUXhSUcZS+584QLHNoq535oiw5sY6zrDp2ptJsaaFzSF1JdMJyIGYSaA9jfvsgVLA9ql0bEcU7GANol5MLXRXiUXPUn7HE9yFbMlTeRhWYxY2wgbmtXH+E6HlPDbpM/mLWjEc/rwykxHoM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783426274; c=relaxed/simple; bh=lu6HEJ+NO53gx6E3nBGy4cNy0TQ86NHcwV2cRfWsIvE=; h=From:To:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=r0h/O8aFNRK0Hmlh+dUjCoDmI2ynwQEmJY5Bam1/gcKU5QYtU6FPHUHL9RZ2SOGRX6kaQBysv3/xX6N+Zpp7gEzj3Dn5UzPeRfDEGJM3oKyTKDKOMs9PH/oddn++rmmI2SZdpzQv6jc+F0/e9o8Vlk1T4KUIKBvwGFY2pfgpmwU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lG/ivu93; 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="lG/ivu93" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3E58B1F00A3D; Tue, 7 Jul 2026 12:11:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783426273; bh=XwJ6GKA+IHkqNyMSjfBb3t8dbQmSfsrV9sf8QDryTGU=; h=From:To:Subject:Date:In-Reply-To:References; b=lG/ivu93c2I8twejB2g47UaFqDnyU+plnX8dqsATjf7M3fJmkWIZnBOk4gyuzfjax GPeopLs+si1anNJtWwQfjVFZ9c0gbCIXT953bmaIef+owJzhVymFDCpbVXPnkmGNbA PTVdgwGPxDnOpK4rPsVXMQIsOqMMcsSGeBJ6kfJKdiZBJALQAAZaKQNKng2T5Nv/Ty WDWChOAccr6HcQogcURoP9UmjNabBMBUaehfc7RGEBJflgZ0pboQZumhysr5EcbULi Jhu0i12RcXsxIbRRV14HwBZmXKNgdZXQMEUwZAjVNnflhitbPIJNuayIQC230ESLVz Vh21knYttmAJQ== From: Lee Jones To: lee@kernel.org, Ping Cheng , Jason Gerecke , Jiri Kosina , Benjamin Tissoires , Aaron Skomra , Dmitry Torokhov , Peter Hutterer , linux-input@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 4/4] HID: wacom: Redesign shared sibling data lifecycle Date: Tue, 7 Jul 2026 12:10:43 +0000 Message-ID: <20260707121051.1683937-4-lee@kernel.org> X-Mailer: git-send-email 2.55.0.rc2.803.g1fd1e6609c-goog In-Reply-To: <20260707121051.1683937-1-lee@kernel.org> References: <20260707121051.1683937-1-lee@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The Wacom driver coordinates state between sibling interfaces of the same physical device using a shared structure 'wacom_shared' inside 'wacom_hdev_data'. The driver kept a volatile representative pointer 'data->dev' pointing to a sibling 'hid_device' for physical path comparisons during sibling matching. This pointer management is fragile. When the representative device is disconnected, wacom_remove_shared_data() failed to clear/update 'data->dev', leading to a Use-After-Free vulnerability when subsequent sibling probes dereference the dangling 'data->dev' pointer. Resolve this issue by redesigning the sibling data lifecycle: - Eliminate the volatile 'data->dev' representative pointer completely - Redesign 'wacom_hdev_data' to store stable static copies of the required attributes upon first allocation: 'phys' path string, 'vendor', 'product' IDs and the sibling's 'device_type' - Use these static attributes for stable sibling matching in wacom_are_sibling() and wacom_get_hdev_data() This ensures sibling matching remains safe and stable even if individual siblings are dynamically added or removed. To secure the lifecycle against concurrent probe/disconnect races: - Switch kref_put() to kref_put_mutex() in wacom_remove_shared_data() to serialize refcount drops with list traversal and lookup - Modify wacom_release_shared_data() to assume the list lock is already held Also, do not accumulate the 'device_type' capability flag during subsequent sibling probes. Keeping only the first probed sibling's device_type exactly preserves the original sibling matching behavior without introducing side effects. Fixes: 4492efffffeb ("Input: wacom - share pen info with touch of the same ID") Signed-off-by: Lee Jones --- v1 -> v2: Split and use RCU as per Dmitry's review v2 -> v3: Sashiko fixes v3 -> v4: No change v4 -> v5: No change drivers/hid/wacom_sys.c | 70 +++++++++++++++++++++++++++-------------- 1 file changed, 46 insertions(+), 24 deletions(-) diff --git a/drivers/hid/wacom_sys.c b/drivers/hid/wacom_sys.c index 3990d8d0b40c..9fb9dde7dd73 100644 --- a/drivers/hid/wacom_sys.c +++ b/drivers/hid/wacom_sys.c @@ -759,27 +759,47 @@ static void wacom_retrieve_hid_descriptor(struct hid_device *hdev, struct wacom_hdev_data { struct list_head list; struct kref kref; - struct hid_device *dev; + char phys[64]; + __u32 vendor; + __u32 product; + __u32 device_type; struct wacom_shared shared; }; +static bool wacom_compare_device_paths(struct hid_device *hdev_a, + const char *phys_b, char separator) +{ + const char *p1 = strrchr(hdev_a->phys, separator); + const char *p2 = strrchr(phys_b, separator); + int n1, n2; + + if (!p1 || !p2) + return false; + + n1 = p1 - hdev_a->phys; + n2 = p2 - phys_b; + + if (n1 != n2 || n1 <= 0 || n2 <= 0) + return false; + + return !strncmp(hdev_a->phys, phys_b, n1); +} + static LIST_HEAD(wacom_udev_list); static DEFINE_MUTEX(wacom_udev_list_lock); static bool wacom_are_sibling(struct hid_device *hdev, - struct hid_device *sibling) + struct wacom_hdev_data *data) { struct wacom *wacom = hid_get_drvdata(hdev); struct wacom_features *features = &wacom->wacom_wac.features; - struct wacom *sibling_wacom = hid_get_drvdata(sibling); - struct wacom_features *sibling_features = &sibling_wacom->wacom_wac.features; __u32 oVid = features->oVid ? features->oVid : hdev->vendor; __u32 oPid = features->oPid ? features->oPid : hdev->product; /* The defined oVid/oPid must match that of the sibling */ - if (features->oVid != HID_ANY_ID && sibling->vendor != oVid) + if (features->oVid != HID_ANY_ID && data->vendor != oVid) return false; - if (features->oPid != HID_ANY_ID && sibling->product != oPid) + if (features->oPid != HID_ANY_ID && data->product != oPid) return false; /* @@ -787,11 +807,11 @@ static bool wacom_are_sibling(struct hid_device *hdev, * device path, while those with different VID/PID must share * the same physical parent device path. */ - if (hdev->vendor == sibling->vendor && hdev->product == sibling->product) { - if (!hid_compare_device_paths(hdev, sibling, '/')) + if (hdev->vendor == data->vendor && hdev->product == data->product) { + if (!wacom_compare_device_paths(hdev, data->phys, '/')) return false; } else { - if (!hid_compare_device_paths(hdev, sibling, '.')) + if (!wacom_compare_device_paths(hdev, data->phys, '.')) return false; } @@ -804,7 +824,7 @@ static bool wacom_are_sibling(struct hid_device *hdev, * devices. */ if ((features->device_type & WACOM_DEVICETYPE_DIRECT) && - !(sibling_features->device_type & WACOM_DEVICETYPE_DIRECT)) + !(data->device_type & WACOM_DEVICETYPE_DIRECT)) return false; /* @@ -812,17 +832,17 @@ static bool wacom_are_sibling(struct hid_device *hdev, * devices. */ if (!(features->device_type & WACOM_DEVICETYPE_DIRECT) && - (sibling_features->device_type & WACOM_DEVICETYPE_DIRECT)) + (data->device_type & WACOM_DEVICETYPE_DIRECT)) return false; /* Pen devices may only be siblings of touch devices */ if ((features->device_type & WACOM_DEVICETYPE_PEN) && - !(sibling_features->device_type & WACOM_DEVICETYPE_TOUCH)) + !(data->device_type & WACOM_DEVICETYPE_TOUCH)) return false; /* Touch devices may only be siblings of pen devices */ if ((features->device_type & WACOM_DEVICETYPE_TOUCH) && - !(sibling_features->device_type & WACOM_DEVICETYPE_PEN)) + !(data->device_type & WACOM_DEVICETYPE_PEN)) return false; /* @@ -838,7 +858,7 @@ static struct wacom_hdev_data *wacom_get_hdev_data(struct hid_device *hdev) /* Try to find an already-probed interface from the same device */ list_for_each_entry(data, &wacom_udev_list, list) { - if (hid_compare_device_paths(hdev, data->dev, '/')) { + if (wacom_compare_device_paths(hdev, data->phys, '/')) { kref_get(&data->kref); return data; } @@ -846,7 +866,7 @@ static struct wacom_hdev_data *wacom_get_hdev_data(struct hid_device *hdev) /* Fallback to finding devices that appear to be "siblings" */ list_for_each_entry(data, &wacom_udev_list, list) { - if (wacom_are_sibling(hdev, data->dev)) { + if (wacom_are_sibling(hdev, data)) { kref_get(&data->kref); return data; } @@ -860,18 +880,15 @@ static void wacom_release_shared_data(struct kref *kref) struct wacom_hdev_data *data = container_of(kref, struct wacom_hdev_data, kref); - mutex_lock(&wacom_udev_list_lock); list_del(&data->list); - mutex_unlock(&wacom_udev_list_lock); - kfree(data); } static void wacom_remove_shared_data(void *res) { - struct wacom *wacom = res; + struct wacom *res_wacom = res; struct wacom_hdev_data *data; - struct wacom_wac *wacom_wac = &wacom->wacom_wac; + struct wacom_wac *wacom_wac = &res_wacom->wacom_wac; if (wacom_wac->shared) { data = container_of(wacom_wac->shared, struct wacom_hdev_data, @@ -885,17 +902,19 @@ static void wacom_remove_shared_data(void *res) rcu_dereference_protected(wacom_wac->shared->pen, lockdep_is_held(&wacom_udev_list_lock)); - if (touch == wacom->hdev) { + if (touch == res_wacom->hdev) { rcu_assign_pointer(wacom_wac->shared->touch, NULL); rcu_assign_pointer(wacom_wac->shared->touch_input, NULL); - } else if (pen == wacom->hdev) { + } else if (pen == res_wacom->hdev) { rcu_assign_pointer(wacom_wac->shared->pen, NULL); } } synchronize_rcu(); - kref_put(&data->kref, wacom_release_shared_data); + if (kref_put_mutex(&data->kref, wacom_release_shared_data, &wacom_udev_list_lock)) + mutex_unlock(&wacom_udev_list_lock); + wacom_wac->shared = NULL; } } @@ -918,7 +937,10 @@ static int wacom_add_shared_data(struct hid_device *hdev) } kref_init(&data->kref); - data->dev = hdev; + strscpy(data->phys, hdev->phys, sizeof(data->phys)); + data->vendor = hdev->vendor; + data->product = hdev->product; + data->device_type = wacom_wac->features.device_type; list_add_tail(&data->list, &wacom_udev_list); } -- 2.55.0.rc2.803.g1fd1e6609c-goog