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 X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 12B66C33C8C for ; Mon, 6 Jan 2020 15:53:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E363E2075A for ; Mon, 6 Jan 2020 15:53:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726536AbgAFPxl (ORCPT ); Mon, 6 Jan 2020 10:53:41 -0500 Received: from mx2.suse.de ([195.135.220.15]:39202 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726463AbgAFPxl (ORCPT ); Mon, 6 Jan 2020 10:53:41 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 42DB1AD0F; Mon, 6 Jan 2020 15:53:39 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id 593D3DA78B; Mon, 6 Jan 2020 16:53:29 +0100 (CET) Date: Mon, 6 Jan 2020 16:53:28 +0100 From: David Sterba To: Cengiz Can Cc: linux-btrfs@vger.kernel.org, Chris Mason , Josef Bacik , David Sterba Subject: Re: [PATCH] fs: btrfs: prevent unintentional int overflow Message-ID: <20200106155328.GK3929@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Cengiz Can , linux-btrfs@vger.kernel.org, Chris Mason , Josef Bacik , David Sterba References: <20200103184739.26903-1-cengiz@kernel.wtf> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200103184739.26903-1-cengiz@kernel.wtf> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Fri, Jan 03, 2020 at 01:47:40PM -0500, Cengiz Can wrote: > Coverity scan for 5.5.0-rc4 found a possible integer overflow in > tree-checker.c line 364. > > `prev_csum_end = (prev_item_size / csumsize) * sectorsize;` > > Quoting from scan results: > > ``` > CID 1456959 Unintentional integer overflow > > Unintentional integer overflow (OVERFLOW_BEFORE_WIDEN) overflow_before_widen: > Potentially overflowing expression `prev_item_size / csumsize * sectorsize` > with type unsigned int (32 bits, unsigned) is evaluated using 32-bit > arithmetic, and then used in a context that expects an expression of type u64. > (64 bits, unsigned). > ``` > > Added a cast to `u64` on the left hand side of the expression. > > Compiles fine on x86_64_defconfig with all btrfs config flags enabled. > > Signed-off-by: Cengiz Can > --- > fs/btrfs/tree-checker.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c > index 97f3520b8d98..9f58f07be779 100644 > --- a/fs/btrfs/tree-checker.c > +++ b/fs/btrfs/tree-checker.c > @@ -361,7 +361,7 @@ static int check_csum_item(struct extent_buffer *leaf, struct btrfs_key *key, > u32 prev_item_size; > > prev_item_size = btrfs_item_size_nr(leaf, slot - 1); > - prev_csum_end = (prev_item_size / csumsize) * sectorsize; > + prev_csum_end = (u64) (prev_item_size / csumsize) * sectorsize; The overflow can't happen in practice. Taking generous maximum value for an item and sectorsize (64K) and doing the math will reach nowhere the overflow limit for 32bit type: 64K / 4 * 64K = 1G I'm not sure if this is worth adding the cast, or mark the coverity issue as not important.