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 <[email protected]> --- v6: - Rename REVOCABLE_TRY_ACCESS_WITH() -> REVOCABLE_TRY_ACCESS_SCOPED(). - Use new REVOCABLE_TRY_ACCESS_WITH() if applicable. v4-v5: - Doesn't exist. v3: https://lore.kernel.org/chrome-platform/[email protected]/ - Use specific labels for different cleanup in cros_ec_chardev_open(). v2: https://lore.kernel.org/chrome-platform/[email protected] - Rename "ref_proxy" -> "revocable". - Fix a sparse warning by removing the redundant __rcu annotation. v1: https://lore.kernel.org/chrome-platform/[email protected] drivers/platform/chrome/cros_ec_chardev.c | 71 ++++++++++++++++++----- 1 file changed, 56 insertions(+), 15 deletions(-) diff --git a/drivers/platform/chrome/cros_ec_chardev.c b/drivers/platform/chrome/cros_ec_chardev.c index c9d80ad5b57e..bc152c206fb8 100644 --- a/drivers/platform/chrome/cros_ec_chardev.c +++ b/drivers/platform/chrome/cros_ec_chardev.c @@ -22,6 +22,7 @@ #include <linux/platform_data/cros_ec_proto.h> #include <linux/platform_device.h> #include <linux/poll.h> +#include <linux/revocable.h> #include <linux/slab.h> #include <linux/types.h> #include <linux/uaccess.h> @@ -32,7 +33,7 @@ #define CROS_MAX_EVENT_LEN PAGE_SIZE 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; msg = kzalloc(sizeof(*msg) + sizeof(*resp), GFP_KERNEL); @@ -64,7 +66,13 @@ static int ec_get_version(struct chardev_priv *priv, char *str, int maxlen) msg->command = EC_CMD_GET_VERSION + priv->cmd_offset; msg->insize = sizeof(*resp); - ret = cros_ec_cmd_xfer_status(priv->ec_dev, msg); + REVOCABLE_TRY_ACCESS_WITH(priv->ec_dev_rev, ec_dev); + if (!ec_dev) { + ret = -ENODEV; + goto exit; + } + + ret = cros_ec_cmd_xfer_status(ec_dev, msg); if (ret < 0) { snprintf(str, maxlen, "Unknown EC version, returned error: %d\n", @@ -92,10 +100,17 @@ static int cros_ec_chardev_mkbp_event(struct notifier_block *nb, { struct chardev_priv *priv = container_of(nb, struct chardev_priv, notifier); - struct cros_ec_device *ec_dev = priv->ec_dev; + struct cros_ec_device *ec_dev; struct ec_event *event; - unsigned long event_bit = 1 << ec_dev->event_data.event_type; - int total_size = sizeof(*event) + ec_dev->event_size; + unsigned long event_bit; + int total_size; + + REVOCABLE_TRY_ACCESS_WITH(priv->ec_dev_rev, ec_dev); + if (!ec_dev) + return NOTIFY_DONE; + + event_bit = 1 << ec_dev->event_data.event_type; + total_size = sizeof(*event) + ec_dev->event_size; if (!(event_bit & priv->event_mask) || (priv->event_len + total_size) > CROS_MAX_EVENT_LEN) @@ -166,7 +181,12 @@ static int cros_ec_chardev_open(struct inode *inode, struct file *filp) if (!priv) return -ENOMEM; - priv->ec_dev = ec_dev; + priv->ec_dev_rev = revocable_alloc(ec_dev->revocable_provider); + if (!priv->ec_dev_rev) { + ret = -ENOMEM; + goto free_priv; + } + priv->cmd_offset = ec->cmd_offset; filp->private_data = priv; INIT_LIST_HEAD(&priv->events); @@ -178,9 +198,14 @@ static int cros_ec_chardev_open(struct inode *inode, struct file *filp) &priv->notifier); if (ret) { dev_err(ec_dev->dev, "failed to register event notifier\n"); - kfree(priv); + goto free_revocable; } + return 0; +free_revocable: + revocable_free(priv->ec_dev_rev); +free_priv: + kfree(priv); return ret; } @@ -251,11 +276,15 @@ 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 = filp->private_data; - struct cros_ec_device *ec_dev = priv->ec_dev; + struct cros_ec_device *ec_dev; struct ec_event *event, *e; - blocking_notifier_chain_unregister(&ec_dev->event_notifier, - &priv->notifier); + REVOCABLE_TRY_ACCESS_SCOPED(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); list_for_each_entry_safe(event, e, &priv->events, node) { list_del(&event->node); @@ -273,6 +302,7 @@ static long cros_ec_chardev_ioctl_xcmd(struct chardev_priv *priv, void __user *a { struct cros_ec_command *s_cmd; struct cros_ec_command u_cmd; + struct cros_ec_device *ec_dev; long ret; if (copy_from_user(&u_cmd, arg, sizeof(u_cmd))) @@ -299,10 +329,17 @@ static long cros_ec_chardev_ioctl_xcmd(struct chardev_priv *priv, void __user *a } s_cmd->command += priv->cmd_offset; - ret = cros_ec_cmd_xfer(priv->ec_dev, s_cmd); - /* Only copy data to userland if data was received. */ - if (ret < 0) - goto exit; + REVOCABLE_TRY_ACCESS_SCOPED(priv->ec_dev_rev, ec_dev) { + if (!ec_dev) { + ret = -ENODEV; + goto exit; + } + + ret = cros_ec_cmd_xfer(ec_dev, s_cmd); + /* Only copy data to userland if data was received. */ + if (ret < 0) + goto exit; + } if (copy_to_user(arg, s_cmd, sizeof(*s_cmd) + s_cmd->insize)) ret = -EFAULT; @@ -313,10 +350,14 @@ static long cros_ec_chardev_ioctl_xcmd(struct chardev_priv *priv, void __user *a static long cros_ec_chardev_ioctl_readmem(struct chardev_priv *priv, void __user *arg) { - struct cros_ec_device *ec_dev = priv->ec_dev; + struct cros_ec_device *ec_dev; struct cros_ec_readmem s_mem = { }; long num; + REVOCABLE_TRY_ACCESS_WITH(priv->ec_dev_rev, ec_dev); + if (!ec_dev) + return -ENODEV; + /* Not every platform supports direct reads */ if (!ec_dev->cmd_readmem) return -ENOTTY; -- 2.48.1
