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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 45BCFC2BA83 for ; Fri, 14 Feb 2020 16:09:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1341724682 for ; Fri, 14 Feb 2020 16:09:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581696592; bh=bKdze+iTRjZ+6yDQsmCbsOAAgJXbF6/hex2eF8Vicfc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=NBA8uivctItH8WA6htJm8bzIzhDwQ1Ymrr9iVPP8u3G5ZZ2RBAkcyJB6ikNI1oT1e s+3oRBQbgnslNPMJB74GdROsXXciNaKLfSf01np7yZUeyxaLAt/sUcF28A+tzkC2rN JbI7mZYRAi6ZubzZpxCS7wgyTc98lh6keuf3WJyo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390861AbgBNQJv (ORCPT ); Fri, 14 Feb 2020 11:09:51 -0500 Received: from mail.kernel.org ([198.145.29.99]:34004 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391291AbgBNQJb (ORCPT ); Fri, 14 Feb 2020 11:09:31 -0500 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0F5062468D; Fri, 14 Feb 2020 16:09:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581696570; bh=bKdze+iTRjZ+6yDQsmCbsOAAgJXbF6/hex2eF8Vicfc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=inuNYD8URlA57gUjyN97JkZL7glWJcmk7hOljJnGJG73CHob4UiZDpAtFTCknQjnO kwbyFTXkYB40ScaItPDGZoR6b3wK2QWY6+ZZ2g0avw5Wn4Z8hvxjQDXzbqR4xCkRjy v30O6yLP+qvadTgRwyLwn/hfF1JBBLvtIkVRhlnU= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: David Sterba , Dan Carpenter , Josef Bacik , Sasha Levin , linux-btrfs@vger.kernel.org Subject: [PATCH AUTOSEL 5.4 360/459] btrfs: safely advance counter when looking up bio csums Date: Fri, 14 Feb 2020 11:00:10 -0500 Message-Id: <20200214160149.11681-360-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200214160149.11681-1-sashal@kernel.org> References: <20200214160149.11681-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: David Sterba [ Upstream commit 4babad10198fa73fe73239d02c2e99e3333f5f5c ] Dan's smatch tool reports fs/btrfs/file-item.c:295 btrfs_lookup_bio_sums() warn: should this be 'count == -1' which points to the while (count--) loop. With count == 0 the check itself could decrement it to -1. There's a WARN_ON a few lines below that has never been seen in practice though. It turns out that the value of page_bytes_left matches the count (by sectorsize multiples). The loop never reaches the state where count would go to -1, because page_bytes_left == 0 is found first and this breaks out. For clarity, use only plain check on count (and only for positive value), decrement safely inside the loop. Any other discrepancy after the whole bio list processing should be reported by the exising WARN_ON_ONCE as well. Reported-by: Dan Carpenter Reviewed-by: Josef Bacik Signed-off-by: David Sterba Signed-off-by: Sasha Levin --- fs/btrfs/file-item.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c index c878bc25d0460..f62a179f85bb6 100644 --- a/fs/btrfs/file-item.c +++ b/fs/btrfs/file-item.c @@ -274,7 +274,8 @@ static blk_status_t __btrfs_lookup_bio_sums(struct inode *inode, struct bio *bio csum += count * csum_size; nblocks -= count; next: - while (count--) { + while (count > 0) { + count--; disk_bytenr += fs_info->sectorsize; offset += fs_info->sectorsize; page_bytes_left -= fs_info->sectorsize; -- 2.20.1