diff options
| -rw-r--r-- | drivers/input/misc/keychord.c | 61 |
1 files changed, 60 insertions, 1 deletions
diff --git a/drivers/input/misc/keychord.c b/drivers/input/misc/keychord.c index c5ab3ddda456..1673e4239403 100644 --- a/drivers/input/misc/keychord.c +++ b/drivers/input/misc/keychord.c @@ -60,6 +60,10 @@ struct keychord_device { unsigned char head; unsigned char tail; __u16 buff[BUFFER_SIZE]; + /* Bit to serialize writes to this device */ +#define KEYCHORD_BUSY 0x01 + unsigned long flags; + wait_queue_head_t write_waitq; }; static int check_keychord(struct keychord_device *kdev, @@ -172,7 +176,6 @@ static int keychord_connect(struct input_handler *handler, goto err_input_open_device; pr_info("keychord: using input dev %s for fevent\n", dev->name); - return 0; err_input_open_device: @@ -225,6 +228,41 @@ static ssize_t keychord_read(struct file *file, char __user *buffer, } /* + * serializes writes on a device. can use mutex_lock_interruptible() + * for this particular use case as well - a matter of preference. + */ +static int +keychord_write_lock(struct keychord_device *kdev) +{ + int ret; + unsigned long flags; + + spin_lock_irqsave(&kdev->lock, flags); + while (kdev->flags & KEYCHORD_BUSY) { + spin_unlock_irqrestore(&kdev->lock, flags); + ret = wait_event_interruptible(kdev->write_waitq, + ((kdev->flags & KEYCHORD_BUSY) == 0)); + if (ret) + return ret; + spin_lock_irqsave(&kdev->lock, flags); + } + kdev->flags |= KEYCHORD_BUSY; + spin_unlock_irqrestore(&kdev->lock, flags); + return 0; +} + +static void +keychord_write_unlock(struct keychord_device *kdev) +{ + unsigned long flags; + + spin_lock_irqsave(&kdev->lock, flags); + kdev->flags &= ~KEYCHORD_BUSY; + spin_unlock_irqrestore(&kdev->lock, flags); + wake_up_interruptible(&kdev->write_waitq); +} + +/* * keychord_write is used to configure the driver */ static ssize_t keychord_write(struct file *file, const char __user *buffer, @@ -250,6 +288,22 @@ static ssize_t keychord_write(struct file *file, const char __user *buffer, return -EFAULT; } + /* + * Serialize writes to this device to prevent various races. + * 1) writers racing here could do duplicate input_unregister_handler() + * calls, resulting in attempting to unlink a node from a list that + * does not exist. + * 2) writers racing here could do duplicate input_register_handler() calls + * below, resulting in a duplicate insertion of a node into the list. + * 3) a double kfree of keychords can occur (in the event that + * input_register_handler() fails below. + */ + ret = keychord_write_lock(kdev); + if (ret) { + kfree(keychords); + return ret; + } + /* unregister handler before changing configuration */ if (kdev->registered) { input_unregister_handler(&kdev->input_handler); @@ -318,15 +372,19 @@ static ssize_t keychord_write(struct file *file, const char __user *buffer, if (ret) { kfree(keychords); kdev->keychords = 0; + keychord_write_unlock(kdev); return ret; } kdev->registered = 1; + keychord_write_unlock(kdev); + return count; err_unlock_return: spin_unlock_irqrestore(&kdev->lock, flags); kfree(keychords); + keychord_write_unlock(kdev); return -EINVAL; } @@ -352,6 +410,7 @@ static int keychord_open(struct inode *inode, struct file *file) spin_lock_init(&kdev->lock); init_waitqueue_head(&kdev->waitq); + init_waitqueue_head(&kdev->write_waitq); kdev->input_handler.event = keychord_event; kdev->input_handler.connect = keychord_connect; |