From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752027AbcJDP2I (ORCPT ); Tue, 4 Oct 2016 11:28:08 -0400 Received: from mga07.intel.com ([134.134.136.100]:27866 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751541AbcJDP2G (ORCPT ); Tue, 4 Oct 2016 11:28:06 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.31,295,1473145200"; d="scan'208";a="16091022" Date: Tue, 4 Oct 2016 21:06:45 +0530 From: Vinod Koul To: Linus Walleij Cc: Joe Perches , Colin King , Dan Williams , "linux-arm-kernel@lists.infradead.org" , dmaengine@vger.kernel.org, "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] dmaengine: coh901318: fix integer overflow when shifting more than 32 places Message-ID: <20161004153645.GG2467@localhost> References: <20160929175725.14157-1-colin.king@canonical.com> <1475172392.2027.12.camel@perches.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 04, 2016 at 02:23:51PM +0200, Linus Walleij wrote: > On Thu, Sep 29, 2016 at 8:06 PM, Joe Perches wrote: > > On Thu, 2016-09-29 at 18:57 +0100, Colin King wrote: > >> Currently U300_DMA_CHANNELS is set to 40, meaning that the shift of 1 can > >> be more than 32 places, which leads to a 32 bit integer overflow. Fix this > >> by casting 1 to a u64 (the same type as started_channels) before shifting > >> it. > > > > trivia: > > > >> diff --git a/drivers/dma/coh901318.c b/drivers/dma/coh901318.c > > [] > >> @@ -1353,7 +1353,7 @@ static ssize_t coh901318_debugfs_read(struct file *file, char __user *buf, > >> tmp += sprintf(tmp, "DMA -- enabled dma channels\n"); > >> > >> for (i = 0; i < U300_DMA_CHANNELS; i++) > >> - if (started_channels & (1 << i)) > >> + if (started_channels & ((u64)1 << i)) > > > > Using > > > > if (started_channels & (1ULL << i)) > > > > would be more common. > > Even better (IMO): > > #include > > if (started_channels & BIT(i)) > > Apparently code is there to avoid the bit 31 problem, mea culpa. I have already applied this one, so feel free to send this as an update :) -- ~Vinod