From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C1132C433EF for ; Mon, 27 Sep 2021 14:47:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A689460FD7 for ; Mon, 27 Sep 2021 14:47:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234909AbhI0OtK (ORCPT ); Mon, 27 Sep 2021 10:49:10 -0400 Received: from mail.kernel.org ([198.145.29.99]:46994 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234799AbhI0OtK (ORCPT ); Mon, 27 Sep 2021 10:49:10 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id AA79960FC2; Mon, 27 Sep 2021 14:47:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1632754052; bh=adeXHUS73Lj4zzzb/ETuBZ3Thy9j9oPRwZgoXcZ7QtI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KY8V7Rjf4MkCkhxYzzkzdHSNH6rbG3D5QDqXAOskiwC5yZMY4FFU1wVvw/NWMfupo Td3hW8o6PB3ZF3RSOmcRMGMZfMfFQ51S2qZMNImcn1ZVuGLk7N71b4kDUGdk+ZL4nC q6/n3a2kzGmzhNJFqCblYhdJosOHaR5/YazgacjJxShd+rwzfpB7bZIFLU2cZPYzjX s69SWf2hO0wk1rgm7ouxc/WMdLYokIpimbREqJCQsR/cF2AnQICM7d5i20N/tJE8ZO fiEUGoXvmFUNV/Y897l2weu/v3XP3YpmPnbboRRc7l1puXpcmu0FB3+4WBfk0lbADq 53WfbxZXnE09Q== Date: Mon, 27 Sep 2021 09:51:31 -0500 From: "Gustavo A. R. Silva" To: Len Baker Cc: Alexander Viro , Kees Cook , linux-fsdevel@vger.kernel.org, linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] writeback: prefer struct_size over open coded arithmetic Message-ID: <20210927145131.GB168427@embeddedor> References: <20210925114308.11455-1-len.baker@gmx.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210925114308.11455-1-len.baker@gmx.com> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Sat, Sep 25, 2021 at 01:43:08PM +0200, Len Baker wrote: > As noted in the "Deprecated Interfaces, Language Features, Attributes, > and Conventions" documentation [1], size calculations (especially > multiplication) should not be performed in memory allocator (or similar) > function arguments due to the risk of them overflowing. This could lead > to values wrapping around and a smaller allocation being made than the > caller was expecting. Using those allocations could lead to linear > overflows of heap memory and other misbehaviors. > > In this case these are not actually dynamic sizes: all the operands > involved in the calculation are constant values. However it is better to > refactor them anyway, just to keep the open-coded math idiom out of > code. > > So, use the struct_size() helper to do the arithmetic instead of the > argument "size + count * size" in the kzalloc() functions. > > This code was detected with the help of Coccinelle and audited and fixed > manually. > > [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments > > Signed-off-by: Len Baker Reviewed-by: Gustavo A. R. Silva Thanks -- Gustavo > --- > Changelog v1 -> v2 > - Rebase against v5.15-rc2 > - Refactor another instance in the same file (Gustavo A. R. Silva). > - Update the commit changelog to inform that this code was detected > using a Coccinelle script (Gustavo A. R. Silva). > > fs/fs-writeback.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c > index 81ec192ce067..5eb0ada7468c 100644 > --- a/fs/fs-writeback.c > +++ b/fs/fs-writeback.c > @@ -566,7 +566,7 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id) > if (atomic_read(&isw_nr_in_flight) > WB_FRN_MAX_IN_FLIGHT) > return; > > - isw = kzalloc(sizeof(*isw) + 2 * sizeof(struct inode *), GFP_ATOMIC); > + isw = kzalloc(struct_size(isw, inodes, 2), GFP_ATOMIC); > if (!isw) > return; > > @@ -624,8 +624,8 @@ bool cleanup_offline_cgwb(struct bdi_writeback *wb) > int nr; > bool restart = false; > > - isw = kzalloc(sizeof(*isw) + WB_MAX_INODES_PER_ISW * > - sizeof(struct inode *), GFP_KERNEL); > + isw = kzalloc(struct_size(isw, inodes, WB_MAX_INODES_PER_ISW), > + GFP_KERNEL); > if (!isw) > return restart; > > -- > 2.25.1 >