[PATCH 3.13.y-ckt 143/143] HID: i2c-hid: Limit reads to wMaxInputLength bytes for input events

[Kamal Mostafa]

3.13.11-ckt18 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Seth Forshee <seth.forshee at canonical.com>

commit 6d00f37e49d95e640a3937a4a1ae07dbe92a10cb upstream.

d1c7e29e8d27 (HID: i2c-hid: prevent buffer overflow in early IRQ)
changed hid_get_input() to read ihid->bufsize bytes, which can be
more than wMaxInputLength. This is the case with the Dell XPS 13
9343, and it is causing events to be missed. In some cases the
missed events are releases, which can cause the cursor to jump or
freeze, among other problems. Limit the number of bytes read to
min(wMaxInputLength, ihid->bufsize) to prevent such problems.

Fixes: d1c7e29e8d27 "HID: i2c-hid: prevent buffer overflow in early IRQ"
Signed-off-by: Seth Forshee <seth.forshee at canonical.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires at redhat.com>
Signed-off-by: Jiri Kosina <jkosina at suse.cz>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/hid/i2c-hid/i2c-hid.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/i2c-hid/i2c-hid.c b/drivers/hid/i2c-hid/i2c-hid.c
index 05c2134..cc4b092 100644
--- a/drivers/hid/i2c-hid/i2c-hid.c
+++ b/drivers/hid/i2c-hid/i2c-hid.c
@@ -356,7 +356,10 @@ static int i2c_hid_hwreset(struct i2c_client *client)
 static void i2c_hid_get_input(struct i2c_hid *ihid)
 {
 	int ret, ret_size;
-	int size = ihid->bufsize;
+	int size = le16_to_cpu(ihid->hdesc.wMaxInputLength);
+
+	if (size > ihid->bufsize)
+		size = ihid->bufsize;
 
 	ret = i2c_master_recv(ihid->client, ihid->inbuf, size);
 	if (ret != size) {
-- 
1.9.1