From nobody Sat Oct 4 19:16:46 2025 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 D1A512EF644; Thu, 14 Aug 2025 09:13:06 +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=1755162787; cv=none; b=ZfJcmlsr3/31hnQmtk4wyUiAVEtYUOz/EflTnOztDtLMtTPMIGQXTyDYllZJzraddwF9Z4M7qY+NlkLct4MjfsUaRFiT0NULToTATDRO/Pg4BcqdGb6Y67UHiQBwennv9cHf9iuCCrkOvZwcARMHgxmyl5KmMPrizQkPKDWSeKE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755162787; c=relaxed/simple; bh=TBXf9TlITbl7kntH3GIMV20rolg0uvfkE9lfCdNPb+4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=eqLIUbsmW+987Gsy6BYAKbpJa9q4QTDNS4OEiDigTxZG6uDfYtSkrBv6LZAfv303J9lwBugSX3G22MwKATexp/ztHgufRqQD0mcW3Z5Wgk9oyZn0/r+/brYpvGv+xazUg/CYS7w5IKPsvmiR/dYdD2V4863OJZhmqAvfHYLwwKE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VN23y8pb; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="VN23y8pb" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3B21CC4CEFA; Thu, 14 Aug 2025 09:13:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1755162786; bh=TBXf9TlITbl7kntH3GIMV20rolg0uvfkE9lfCdNPb+4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=VN23y8pbqqlmt6tFYwlOJ1z1eGvrjZE/jLEjPRXQau6t4UzWNeTwseKrPdi72GaTX 9fBABkCYry94P3y5AQzqeFT+qDeooYGretDmUClN8UxQWfUvl0Ro805EM8EVMmQDwO 2jP9MH/QGK2bSdItJjtJbZjKvWIDnv4spp41+fUGFILXSYpagZMUt5yAvjbPrY1h3Z GlJa+IEzPPy5ekgvUYtzbBkCF8DkHvCPymkP0QUSKk091+4EplYAlQFati/EAIr9Ag 1Are5J8+c22UXAZO/rR5WJb42ps4Z6o/tyKW6EIxQQxFtxYulxAdYtBdd7zMbQ1rPA L1MKgI6WSDJ+w== From: Tzung-Bi Shih To: bleung@chromium.org Cc: tzungbi@kernel.org, dawidn@google.com, chrome-platform@lists.linux.dev, akpm@linux-foundation.org, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org Subject: [PATCH 3/3] platform/chrome: cros_ec_chardev: Consume cros_ec_device via ref_proxy Date: Thu, 14 Aug 2025 09:10:20 +0000 Message-ID: <20250814091020.1302888-4-tzungbi@kernel.org> X-Mailer: git-send-email 2.51.0.rc1.163.g2494970778-goog In-Reply-To: <20250814091020.1302888-1-tzungbi@kernel.org> References: <20250814091020.1302888-1-tzungbi@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: quoted-printable Content-Type: text/plain; charset="utf-8" The cros_ec_chardev driver provides a character device interface to the ChromeOS EC. A file handle to this device can remain open in userspace even if the underlying EC device is removed. This creates a classic use-after-free vulnerability. Any file operation (ioctl, release, etc.) on the open handle after the EC device has gone would access a stale pointer, leading to a system crash. To prevent this, leverage the ref_proxy library and convert cros_ec_chardev to a resource consumer of cros_ec_device. Signed-off-by: Tzung-Bi Shih --- drivers/platform/chrome/cros_ec_chardev.c | 125 +++++++++++++++------- 1 file changed, 85 insertions(+), 40 deletions(-) diff --git a/drivers/platform/chrome/cros_ec_chardev.c b/drivers/platform/c= hrome/cros_ec_chardev.c index c9d80ad5b57e..f4aa70c8b6d4 100644 --- a/drivers/platform/chrome/cros_ec_chardev.c +++ b/drivers/platform/chrome/cros_ec_chardev.c @@ -22,6 +22,7 @@ #include #include #include +#include #include #include #include @@ -32,7 +33,7 @@ #define CROS_MAX_EVENT_LEN PAGE_SIZE =20 struct chardev_priv { - struct cros_ec_device *ec_dev; + struct ref_proxy *ec_dev_proxy; struct notifier_block notifier; wait_queue_head_t wait_event; unsigned long event_mask; @@ -55,6 +56,7 @@ static int ec_get_version(struct chardev_priv *priv, char= *str, int maxlen) }; struct ec_response_get_version *resp; struct cros_ec_command *msg; + struct cros_ec_device __rcu *ec_dev; int ret; =20 msg =3D kzalloc(sizeof(*msg) + sizeof(*resp), GFP_KERNEL); @@ -64,12 +66,19 @@ static int ec_get_version(struct chardev_priv *priv, ch= ar *str, int maxlen) msg->command =3D EC_CMD_GET_VERSION + priv->cmd_offset; msg->insize =3D sizeof(*resp); =20 - ret =3D cros_ec_cmd_xfer_status(priv->ec_dev, msg); - if (ret < 0) { - snprintf(str, maxlen, - "Unknown EC version, returned error: %d\n", - msg->result); - goto exit; + REF_PROXY_GET(priv->ec_dev_proxy, ec_dev) { + if (!ec_dev) { + ret =3D -ENODEV; + goto exit; + } + + ret =3D cros_ec_cmd_xfer_status(ec_dev, msg); + if (ret < 0) { + snprintf(str, maxlen, + "Unknown EC version, returned error: %d\n", + msg->result); + goto exit; + } } =20 resp =3D (struct ec_response_get_version *)msg->data; @@ -92,22 +101,30 @@ static int cros_ec_chardev_mkbp_event(struct notifier_= block *nb, { struct chardev_priv *priv =3D container_of(nb, struct chardev_priv, notifier); - struct cros_ec_device *ec_dev =3D priv->ec_dev; + struct cros_ec_device __rcu *ec_dev; struct ec_event *event; - unsigned long event_bit =3D 1 << ec_dev->event_data.event_type; - int total_size =3D sizeof(*event) + ec_dev->event_size; + unsigned long event_bit; + int total_size; + + REF_PROXY_GET(priv->ec_dev_proxy, ec_dev) { + if (!ec_dev) + return NOTIFY_DONE; =20 - if (!(event_bit & priv->event_mask) || - (priv->event_len + total_size) > CROS_MAX_EVENT_LEN) - return NOTIFY_DONE; + event_bit =3D 1 << ec_dev->event_data.event_type; + total_size =3D sizeof(*event) + ec_dev->event_size; =20 - event =3D kzalloc(total_size, GFP_KERNEL); - if (!event) - return NOTIFY_DONE; + if (!(event_bit & priv->event_mask) || + (priv->event_len + total_size) > CROS_MAX_EVENT_LEN) + return NOTIFY_DONE; =20 - event->size =3D ec_dev->event_size; - event->event_type =3D ec_dev->event_data.event_type; - memcpy(event->data, &ec_dev->event_data.data, ec_dev->event_size); + event =3D kzalloc(total_size, GFP_KERNEL); + if (!event) + return NOTIFY_DONE; + + event->size =3D ec_dev->event_size; + event->event_type =3D ec_dev->event_data.event_type; + memcpy(event->data, &ec_dev->event_data.data, ec_dev->event_size); + } =20 spin_lock(&priv->wait_event.lock); list_add_tail(&event->node, &priv->events); @@ -166,7 +183,12 @@ static int cros_ec_chardev_open(struct inode *inode, s= truct file *filp) if (!priv) return -ENOMEM; =20 - priv->ec_dev =3D ec_dev; + priv->ec_dev_proxy =3D ref_proxy_alloc(ec_dev->ref_proxy_provider); + if (!priv->ec_dev_proxy) { + ret =3D -ENOMEM; + goto err; + } + priv->cmd_offset =3D ec->cmd_offset; filp->private_data =3D priv; INIT_LIST_HEAD(&priv->events); @@ -178,9 +200,14 @@ static int cros_ec_chardev_open(struct inode *inode, s= truct file *filp) &priv->notifier); if (ret) { dev_err(ec_dev->dev, "failed to register event notifier\n"); - kfree(priv); + goto err; } =20 + return 0; +err: + if (priv->ec_dev_proxy) + ref_proxy_free(priv->ec_dev_proxy); + kfree(priv); return ret; } =20 @@ -251,11 +278,16 @@ static ssize_t cros_ec_chardev_read(struct file *filp= , char __user *buffer, static int cros_ec_chardev_release(struct inode *inode, struct file *filp) { struct chardev_priv *priv =3D filp->private_data; - struct cros_ec_device *ec_dev =3D priv->ec_dev; + struct cros_ec_device __rcu *ec_dev; struct ec_event *event, *e; =20 - blocking_notifier_chain_unregister(&ec_dev->event_notifier, - &priv->notifier); + REF_PROXY_GET(priv->ec_dev_proxy, ec_dev) { + if (ec_dev) + blocking_notifier_chain_unregister( + &ec_dev->event_notifier, + &priv->notifier); + } + ref_proxy_free(priv->ec_dev_proxy); =20 list_for_each_entry_safe(event, e, &priv->events, node) { list_del(&event->node); @@ -273,6 +305,7 @@ static long cros_ec_chardev_ioctl_xcmd(struct chardev_p= riv *priv, void __user *a { struct cros_ec_command *s_cmd; struct cros_ec_command u_cmd; + struct cros_ec_device __rcu *ec_dev; long ret; =20 if (copy_from_user(&u_cmd, arg, sizeof(u_cmd))) @@ -299,10 +332,17 @@ static long cros_ec_chardev_ioctl_xcmd(struct chardev= _priv *priv, void __user *a } =20 s_cmd->command +=3D priv->cmd_offset; - ret =3D cros_ec_cmd_xfer(priv->ec_dev, s_cmd); - /* Only copy data to userland if data was received. */ - if (ret < 0) - goto exit; + REF_PROXY_GET(priv->ec_dev_proxy, ec_dev) { + if (!ec_dev) { + ret =3D -ENODEV; + goto exit; + } + + ret =3D cros_ec_cmd_xfer(ec_dev, s_cmd); + /* Only copy data to userland if data was received. */ + if (ret < 0) + goto exit; + } =20 if (copy_to_user(arg, s_cmd, sizeof(*s_cmd) + s_cmd->insize)) ret =3D -EFAULT; @@ -313,24 +353,29 @@ static long cros_ec_chardev_ioctl_xcmd(struct chardev= _priv *priv, void __user *a =20 static long cros_ec_chardev_ioctl_readmem(struct chardev_priv *priv, void = __user *arg) { - struct cros_ec_device *ec_dev =3D priv->ec_dev; + struct cros_ec_device __rcu *ec_dev; struct cros_ec_readmem s_mem =3D { }; long num; =20 - /* Not every platform supports direct reads */ - if (!ec_dev->cmd_readmem) - return -ENOTTY; + REF_PROXY_GET(priv->ec_dev_proxy, ec_dev) { + if (!ec_dev) + return -ENODEV; =20 - if (copy_from_user(&s_mem, arg, sizeof(s_mem))) - return -EFAULT; + /* Not every platform supports direct reads */ + if (!ec_dev->cmd_readmem) + return -ENOTTY; =20 - if (s_mem.bytes > sizeof(s_mem.buffer)) - return -EINVAL; + if (copy_from_user(&s_mem, arg, sizeof(s_mem))) + return -EFAULT; =20 - num =3D ec_dev->cmd_readmem(ec_dev, s_mem.offset, s_mem.bytes, - s_mem.buffer); - if (num <=3D 0) - return num; + if (s_mem.bytes > sizeof(s_mem.buffer)) + return -EINVAL; + + num =3D ec_dev->cmd_readmem(ec_dev, s_mem.offset, s_mem.bytes, + s_mem.buffer); + if (num <=3D 0) + return num; + } =20 if (copy_to_user((void __user *)arg, &s_mem, sizeof(s_mem))) return -EFAULT; --=20 2.51.0.rc1.163.g2494970778-goog