Input: uinput - take event lock when fetching events from buffer

When fetching events form device's buffer in uinput_read() we need to
take input device's event_lock to avoid racing with new event delivery.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

1 files changed, 24 insertions, 3 deletions

diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
index 736056897e50..1b4ee4a5c49c 100644
--- a/drivers/input/misc/uinput.c
+++ b/drivers/input/misc/uinput.c
@@ -452,9 +452,28 @@ static ssize_t uinput_write(struct file *file, const char __user *buffer, size_t
         return retval;
 }
 
+static bool uinput_fetch_next_event(struct uinput_device *udev,
+                                    struct input_event *event)
+{
+        bool have_event;
+
+        spin_lock_irq(&udev->dev->event_lock);
+
+        have_event = udev->head != udev->tail;
+        if (have_event) {
+                *event = udev->buff[udev->tail];
+                udev->tail = (udev->tail + 1) % UINPUT_BUFFER_SIZE;
+        }
+
+        spin_unlock_irq(&udev->dev->event_lock);
+
+        return have_event;
+}
+
 static ssize_t uinput_read(struct file *file, char __user *buffer, size_t count, loff_t *ppos)
 {
         struct uinput_device *udev = file->private_data;
+        struct input_event event;
         int retval = 0;
 
         if (udev->state != UIST_CREATED)
@@ -477,12 +496,14 @@ static ssize_t uinput_read(struct file *file, char __user *buffer, size_t count,
                 goto out;
         }
 
-        while (udev->head != udev->tail && retval + input_event_size() <= count) {
-                if (input_event_to_user(buffer + retval, &udev->buff[udev->tail])) {
+        while (retval + input_event_size() <= count &&
+               uinput_fetch_next_event(udev, &event)) {
+
+                if (input_event_to_user(buffer + retval, &event)) {
                         retval = -EFAULT;
                         goto out;
                 }
-                udev->tail = (udev->tail + 1) % UINPUT_BUFFER_SIZE;
+
                 retval += input_event_size();
         }