greybus: fw-management: Free fw-mgmt only after all users are gone
The fw-management driver rightly destroys the char device on
connection-exit, but that doesn't guarantee that all of the users of the
device are gone.
Userspace may still be holding file-descriptor of the char device and
can initiate new ioctl operations. And that *will* lead to kernel crash.
To avoid this issue, manage struct users with kref, manage a list of
'struct fw-mgmt' and start using the structure only after getting its
kref incremented.
The important part is the routine get_fw_mgmt(), which increments the
reference to the struct before returning it to the caller. The list of
fw-mgmt structs in protected with a mutex to avoid any races around
that.
The kref is incremented once the char device is opened and dropped only
when it is closed.
Reported-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
diff --git a/drivers/staging/greybus/fw-management.c b/drivers/staging/greybus/fw-management.c
index 7c2226a..0c73f1e 100644
--- a/drivers/staging/greybus/fw-management.c
+++ b/drivers/staging/greybus/fw-management.c
@@ -24,6 +24,9 @@
struct fw_mgmt {
struct device *parent;
struct gb_connection *connection;
+ struct kref kref;
+ struct list_head node;
+
/* Common id-map for interface and backend firmware requests */
struct ida id_map;
struct mutex mutex;
@@ -32,6 +35,7 @@
struct device *class_device;
dev_t dev_num;
unsigned int timeout_jiffies;
+ bool disabled; /* connection getting disabled */
/* Interface Firmware specific fields */
bool mode_switch_started;
@@ -55,6 +59,48 @@
static struct class *fw_mgmt_class;
static dev_t fw_mgmt_dev_num;
static DEFINE_IDA(fw_mgmt_minors_map);
+static LIST_HEAD(fw_mgmt_list);
+static DEFINE_MUTEX(list_mutex);
+
+static void fw_mgmt_kref_release(struct kref *kref)
+{
+ struct fw_mgmt *fw_mgmt = container_of(kref, struct fw_mgmt, kref);
+
+ ida_destroy(&fw_mgmt->id_map);
+ kfree(fw_mgmt);
+}
+
+/*
+ * All users of fw_mgmt take a reference (from within list_mutex lock), before
+ * they get a pointer to play with. And the structure will be freed only after
+ * the last user has put the reference to it.
+ */
+static void put_fw_mgmt(struct fw_mgmt *fw_mgmt)
+{
+ kref_put(&fw_mgmt->kref, fw_mgmt_kref_release);
+}
+
+/* Caller must call put_fw_mgmt() after using struct fw_mgmt */
+static struct fw_mgmt *get_fw_mgmt(struct cdev *cdev)
+{
+ struct fw_mgmt *fw_mgmt;
+
+ mutex_lock(&list_mutex);
+
+ list_for_each_entry(fw_mgmt, &fw_mgmt_list, node) {
+ if (&fw_mgmt->cdev == cdev) {
+ kref_get(&fw_mgmt->kref);
+ goto unlock;
+ }
+ }
+
+ fw_mgmt = NULL;
+
+unlock:
+ mutex_unlock(&list_mutex);
+
+ return fw_mgmt;
+}
static int fw_mgmt_interface_fw_version_operation(struct fw_mgmt *fw_mgmt,
struct fw_mgmt_ioc_get_fw *fw_info)
@@ -318,10 +364,22 @@
static int fw_mgmt_open(struct inode *inode, struct file *file)
{
- struct fw_mgmt *fw_mgmt = container_of(inode->i_cdev, struct fw_mgmt,
- cdev);
+ struct fw_mgmt *fw_mgmt = get_fw_mgmt(inode->i_cdev);
- file->private_data = fw_mgmt;
+ /* fw_mgmt structure can't get freed until file descriptor is closed */
+ if (fw_mgmt) {
+ file->private_data = fw_mgmt;
+ return 0;
+ }
+
+ return -ENODEV;
+}
+
+static int fw_mgmt_release(struct inode *inode, struct file *file)
+{
+ struct fw_mgmt *fw_mgmt = file->private_data;
+
+ put_fw_mgmt(fw_mgmt);
return 0;
}
@@ -437,18 +495,23 @@
unsigned long arg)
{
struct fw_mgmt *fw_mgmt = file->private_data;
- int ret;
+ int ret = -ENODEV;
/*
- * Serialize ioctls
+ * Serialize ioctls.
*
* We don't want the user to do few operations in parallel. For example,
* updating Interface firmware in parallel for the same Interface. There
* is no need to do things in parallel for speed and we can avoid having
- * complicated for now.
+ * complicated code for now.
+ *
+ * This is also used to protect ->disabled, which is used to check if
+ * the connection is getting disconnected, so that we don't start any
+ * new operations.
*/
mutex_lock(&fw_mgmt->mutex);
- ret = fw_mgmt_ioctl(fw_mgmt, cmd, (void __user *)arg);
+ if (!fw_mgmt->disabled)
+ ret = fw_mgmt_ioctl(fw_mgmt, cmd, (void __user *)arg);
mutex_unlock(&fw_mgmt->mutex);
return ret;
@@ -457,6 +520,7 @@
static const struct file_operations fw_mgmt_fops = {
.owner = THIS_MODULE,
.open = fw_mgmt_open,
+ .release = fw_mgmt_release,
.unlocked_ioctl = fw_mgmt_ioctl_unlocked,
};
@@ -496,10 +560,15 @@
init_completion(&fw_mgmt->completion);
ida_init(&fw_mgmt->id_map);
mutex_init(&fw_mgmt->mutex);
+ kref_init(&fw_mgmt->kref);
+
+ mutex_lock(&list_mutex);
+ list_add(&fw_mgmt->node, &fw_mgmt_list);
+ mutex_unlock(&list_mutex);
ret = gb_connection_enable(connection);
if (ret)
- goto err_destroy_ida;
+ goto err_list_del;
minor = ida_simple_get(&fw_mgmt_minors_map, 0, NUM_MINORS, GFP_KERNEL);
if (minor < 0) {
@@ -532,9 +601,12 @@
ida_simple_remove(&fw_mgmt_minors_map, minor);
err_connection_disable:
gb_connection_disable(connection);
-err_destroy_ida:
- ida_destroy(&fw_mgmt->id_map);
- kfree(fw_mgmt);
+err_list_del:
+ mutex_lock(&list_mutex);
+ list_del(&fw_mgmt->node);
+ mutex_unlock(&list_mutex);
+
+ put_fw_mgmt(fw_mgmt);
return ret;
}
@@ -547,13 +619,33 @@
return;
fw_mgmt = gb_connection_get_data(connection);
+
device_destroy(fw_mgmt_class, fw_mgmt->dev_num);
cdev_del(&fw_mgmt->cdev);
ida_simple_remove(&fw_mgmt_minors_map, MINOR(fw_mgmt->dev_num));
- gb_connection_disable(fw_mgmt->connection);
- ida_destroy(&fw_mgmt->id_map);
- kfree(fw_mgmt);
+ /*
+ * Disallow any new ioctl operations on the char device and wait for
+ * existing ones to finish.
+ */
+ mutex_lock(&fw_mgmt->mutex);
+ fw_mgmt->disabled = true;
+ mutex_unlock(&fw_mgmt->mutex);
+
+ /* All pending greybus operations should have finished by now */
+ gb_connection_disable(fw_mgmt->connection);
+
+ /* Disallow new users to get access to the fw_mgmt structure */
+ mutex_lock(&list_mutex);
+ list_del(&fw_mgmt->node);
+ mutex_unlock(&list_mutex);
+
+ /*
+ * All current users of fw_mgmt would have taken a reference to it by
+ * now, we can drop our reference and wait the last user will get
+ * fw_mgmt freed.
+ */
+ put_fw_mgmt(fw_mgmt);
}
int fw_mgmt_init(void)
