Input: evdev - fix evdev_write return value on partial writes

As was recently brought up on the busybox list
(http://lists.busybox.net/pipermail/busybox/2011-January/074565.html),
evdev_write doesn't properly check the count argument, which will
lead to a return value > count on partial writes if the remaining bytes
are accessible - causing userspace confusion.

Fix it by only handling each full input_event structure and return -EINVAL
if less than 1 struct was written, similar to how it is done in evdev_read.

Reported-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Acked-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

1 files changed, 6 insertions, 4 deletions

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index c8471a2552e7..7f42d3a454d2 100644
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c
@@ -321,6 +321,9 @@ static ssize_t evdev_write(struct file *file, const char __user *buffer,
         struct input_event event;
         int retval;
 
+        if (count < input_event_size())
+                return -EINVAL;
+
         retval = mutex_lock_interruptible(&evdev->mutex);
         if (retval)
                 return retval;
@@ -330,17 +333,16 @@ static ssize_t evdev_write(struct file *file, const char __user *buffer,
                 goto out;
         }
 
-        while (retval < count) {
-
+        do {
                 if (input_event_from_user(buffer + retval, &event)) {
                         retval = -EFAULT;
                         goto out;
                 }
+                retval += input_event_size();
 
                 input_inject_event(&evdev->handle,
                                    event.type, event.code, event.value);
-                retval += input_event_size();
-        }
+        } while (retval + input_event_size() <= count);
 
  out:
         mutex_unlock(&evdev->mutex);