From nobody Sat Oct 4 06:34:46 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 B6A762DA776; Wed, 20 Aug 2025 08:17:35 +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=1755677855; cv=none; b=DmM2n5wKSRUkwabEgdzAkaeB47wa6uPzK9+mrL7Yml0cqdWQo6f1lgdC8vW129xOvH1xJiW40cIoL34EBAD1VYgcbHsGfm15JzdFLeRF5GuAydgBYTd5CN0h6baitCMEXp8abVG8dkU+vPo1uEfOG3/M7yCzTinZzIeoxJAwEJw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755677855; c=relaxed/simple; bh=JMpIgp8YIbrOSw336Fx7Pf1imqt/c5Pc3wWDqKBle34=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=OtjREno3QO1WeA6yBZa4/H407KS+H91hApde1scI97FtWYTT6kdAIORqrYE6k0ZgrjXZCbTVXLsK6U1Y/RpEEj6jPFgxBKBnnlyPBuwCzXopWjha4/zPBn0gySARFAy9CWejHlI/eBmnY13wwzcn5igiJkcRJCUpYANqsQcZWgQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UfJcplxp; 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="UfJcplxp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C1CC9C4CEEB; Wed, 20 Aug 2025 08:17:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1755677855; bh=JMpIgp8YIbrOSw336Fx7Pf1imqt/c5Pc3wWDqKBle34=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UfJcplxpUPDflKOZsWezZeWsG7SqcXhO2qVLnFE1MpovVnbQbdfJIGhqjlB50Zz2V QBPHPE+OooMGlt/sXhN96M57wAN9SlYuJ1S5hFfdq1Y3zbOr+C7yaLlXaL2tZU6U6l M+XMzFcZLGGcger62L/+Fg59ZZRIR2fJiIkxcMfnTXbi5nZi8KaO++AbfNQIXEkE2s hM58INCxce4hJ3xqEOIkpshELZ99An5WP/ux6h+5lIujvnWXDcHM49bEDw4yEY8aFn EdT5rPnT5mVtdP6zcPB3sb2MmwjznUvZqdM+EN+RLmHZqzuum3cHmJSGvAtdRlAW2I chtYEt1F6zOzQ== From: Tzung-Bi Shih To: Benson Leung , Greg Kroah-Hartman , "Rafael J . Wysocki" , Danilo Krummrich Cc: Jonathan Corbet , Shuah Khan , Dawid Niedzwiecki , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, chrome-platform@lists.linux.dev, linux-kselftest@vger.kernel.org, tzungbi@kernel.org Subject: [PATCH v2 5/5] platform/chrome: cros_ec_chardev: Consume cros_ec_device via revocable Date: Wed, 20 Aug 2025 08:16:45 +0000 Message-ID: <20250820081645.847919-6-tzungbi@kernel.org> X-Mailer: git-send-email 2.51.0.rc1.167.g924127e9c0-goog In-Reply-To: <20250820081645.847919-1-tzungbi@kernel.org> References: <20250820081645.847919-1-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 revocable and convert cros_ec_chardev to a resource consumer of cros_ec_device. Signed-off-by: Tzung-Bi Shih --- v2: - Rename "ref_proxy" -> "revocable". - Fix a sparse warning by removing the redundant __rcu annotation. v1: https://lore.kernel.org/chrome-platform/20250814091020.1302888-4-tzungb= i@kernel.org drivers/platform/chrome/cros_ec_chardev.c | 124 +++++++++++++++------- 1 file changed, 84 insertions(+), 40 deletions(-) diff --git a/drivers/platform/chrome/cros_ec_chardev.c b/drivers/platform/c= hrome/cros_ec_chardev.c index c9d80ad5b57e..d41c7f574cf1 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 revocable *ec_dev_rev; 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 *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; + REVOCABLE(priv->ec_dev_rev, 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 *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; + + REVOCABLE(priv->ec_dev_rev, ec_dev) { + if (!ec_dev) + return NOTIFY_DONE; + + event_bit =3D 1 << ec_dev->event_data.event_type; + total_size =3D sizeof(*event) + ec_dev->event_size; =20 - if (!(event_bit & priv->event_mask) || - (priv->event_len + total_size) > CROS_MAX_EVENT_LEN) - return NOTIFY_DONE; + if (!(event_bit & priv->event_mask) || + (priv->event_len + total_size) > CROS_MAX_EVENT_LEN) + return NOTIFY_DONE; =20 - event =3D kzalloc(total_size, GFP_KERNEL); - if (!event) - return NOTIFY_DONE; + event =3D kzalloc(total_size, GFP_KERNEL); + if (!event) + 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->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_rev =3D revocable_alloc(ec_dev->revocable_provider); + if (!priv->ec_dev_rev) { + 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_rev) + revocable_free(priv->ec_dev_rev); + kfree(priv); return ret; } =20 @@ -251,11 +278,15 @@ 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 *ec_dev; struct ec_event *event, *e; =20 - blocking_notifier_chain_unregister(&ec_dev->event_notifier, - &priv->notifier); + REVOCABLE(priv->ec_dev_rev, ec_dev) { + if (ec_dev) + blocking_notifier_chain_unregister(&ec_dev->event_notifier, + &priv->notifier); + } + revocable_free(priv->ec_dev_rev); =20 list_for_each_entry_safe(event, e, &priv->events, node) { list_del(&event->node); @@ -273,6 +304,7 @@ 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 *ec_dev; long ret; =20 if (copy_from_user(&u_cmd, arg, sizeof(u_cmd))) @@ -299,10 +331,17 @@ 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; + REVOCABLE(priv->ec_dev_rev, 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 +352,29 @@ 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 *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; + REVOCABLE(priv->ec_dev_rev, 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.rc1.167.g924127e9c0-goog