Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751309AbdISFWB (ORCPT ); Tue, 19 Sep 2017 01:22:01 -0400 Received: from mx1.gtisc.gatech.edu ([143.215.130.81]:52233 "EHLO mx1.gtisc.gatech.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750867AbdISFWA (ORCPT ); Tue, 19 Sep 2017 01:22:00 -0400 From: Meng Xu To: dh.herrmann@googlemail.com, jikos@kernel.org, benjamin.tissoires@redhat.com, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org Cc: meng.xu@gatech.edu, sanidhya@gatech.edu, taesoo@gatech.edu, Meng Xu Subject: [PATCH] hid/uhid: fix a double-fetch bug when copying event from user Date: Tue, 19 Sep 2017 01:21:37 -0400 Message-Id: <1505798497-22436-1-git-send-email-mengxu.gatech@gmail.com> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1367 Lines: 45 When in_compat_syscall(), a user could make type != UHID_CREATE when get_user(type, buffer) [first fetch] and later make event->type == UHID_CREATE in copy_from_user(event, buffer, ...) [second fetch]. By doing so, an attacker might circumvent the specific logic to handle the type == UHID_CREATE case and later cause undefined behaviors. This patch enforces that event->type is overriden to the type value copied in the first fetch and thus, mitigate this race condition attack. Signed-off-by: Meng Xu --- drivers/hid/uhid.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c index 7f8ff39..4bbfd8a 100644 --- a/drivers/hid/uhid.c +++ b/drivers/hid/uhid.c @@ -448,11 +448,20 @@ static int uhid_event_from_user(const char __user *buffer, size_t len, kfree(compat); return 0; } + /* All others can be copied directly */ - } + if (copy_from_user(event, buffer, min(len, sizeof(*event)))) + return -EFAULT; - if (copy_from_user(event, buffer, min(len, sizeof(*event)))) - return -EFAULT; + /* + * Override type in case the user process rushes to change it + * between two fetches + * */ + event->type = type; + } else { + if (copy_from_user(event, buffer, min(len, sizeof(*event)))) + return -EFAULT; + } return 0; } -- 2.7.4