[PATCH] HID: debug: check length before copy_to_user()

[Daniel Rosenberg]

If our length is greater than the size of the buffer, we
overflow the buffer

Signed-off-by: Daniel Rosenberg <dro...@google.com>
Cc: sta...@vger.kernel.org
---
 drivers/hid/hid-debug.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/hid-debug.c b/drivers/hid/hid-debug.c
index 8469b6964ff64..b48100236df89 100644
--- a/drivers/hid/hid-debug.c
+++ b/drivers/hid/hid-debug.c
@@ -1154,6 +1154,8 @@ static ssize_t hid_debug_events_read(struct file *file, 
char __user *buffer,
                        goto out;
                if (list->tail > list->head) {
                        len = list->tail - list->head;
+                       if (len > count)
+                               len = count;
 
                        if (copy_to_user(buffer + ret, 
&list->hid_debug_buf[list->head], len)) {
                                ret = -EFAULT;
@@ -1163,6 +1165,8 @@ static ssize_t hid_debug_events_read(struct file *file, 
char __user *buffer,
                        list->head += len;
                } else {
                        len = HID_DEBUG_BUFSIZE - list->head;
+                       if (len > count)
+                               len = count;
 
                        if (copy_to_user(buffer, 
&list->hid_debug_buf[list->head], len)) {
                                ret = -EFAULT;
@@ -1170,7 +1174,9 @@ static ssize_t hid_debug_events_read(struct file *file, 
char __user *buffer,
                        }
                        list->head = 0;
                        ret += len;
-                       goto copy_rest;
+                       count -= len;
+                       if (count > 0)
+                               goto copy_rest;
                }
 
        }
-- 
2.18.0.399.gad0ab374a1-goog