From: Guillaume Knispel Subject: [PATCH] poll/select: avoid arithmetic overflow in __estimate_accuracy() Date: Sun, 16 Aug 2009 22:29:21 +0200 Message-ID: <20090816222921.26c92ccd@xilun.lan.proformatique.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: linux-fsdevel@vger.kernel.org, Alexander Viro , Arjan van de Ven , Thomas Gleixner , Heiko Carstens , Andrew Morton , Tejun Heo To: linux-kernel@vger.kernel.org Return-path: Received: from gon.proformatique.com ([91.194.178.5]:47828 "EHLO mx1.corp.proformatique.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751710AbZHPU3U (ORCPT ); Sun, 16 Aug 2009 16:29:20 -0400 Sender: linux-fsdevel-owner@vger.kernel.org List-ID: __estimate_accuracy() was prone to integer overflow, for example if *tv == {2147, 483648000} on a 32 bit computer (or even for delays as small as {429, 500000000} if the task is niced). Because the result was already forced between 0 and 100ms, the effect of the overflow was not too problematic, but the use of the hrtimer range feature was not optimal in overflow cases. This patch ensures that there can not be an integer overflow in this function. Signed-off-by: Guillaume Knispel --- fs/select.c | 14 ++++++++++---- 1 files changed, 10 insertions(+), 4 deletions(-) diff --git a/fs/select.c b/fs/select.c index 8084834..a201fc3 100644 --- a/fs/select.c +++ b/fs/select.c @@ -41,22 +41,28 @@ * better solutions.. */ +#define MAX_SLACK (100 * NSEC_PER_MSEC) + static long __estimate_accuracy(struct timespec *tv) { long slack; int divfactor = 1000; + if (tv->tv_sec < 0) + return 0; + if (task_nice(current) > 0) divfactor = divfactor / 5; + if (tv->tv_sec > MAX_SLACK / (NSEC_PER_SEC/divfactor)) + return MAX_SLACK; + slack = tv->tv_nsec / divfactor; slack += tv->tv_sec * (NSEC_PER_SEC/divfactor); - if (slack > 100 * NSEC_PER_MSEC) - slack = 100 * NSEC_PER_MSEC; + if (slack > MAX_SLACK) + return MAX_SLACK; - if (slack < 0) - slack = 0; return slack; }