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 7450BC3B19F for ; Fri, 14 Feb 2020 16:50:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4CD4724670 for ; Fri, 14 Feb 2020 16:50:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581699012; bh=pNi86Qd8IpSJfMsjvwVOCG2Tki6Im0CYrxAz80yld8E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=2AHHSibhE17lHu2oCbhNWvn8/I/wONmHxWPEpBxKGBZc0RHLjn2ic8K5fzU7xsjn1 azbIeW7vxcOf29Xdsa2TLFF2vM/n0tdlpWNT2oIvgHb65PXopztYYA1WVydfVKvM7N IWSSd+Mxukb25kxxrxWzquO3k1H+ijWLNxDs5JRU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394129AbgBNQuI (ORCPT ); Fri, 14 Feb 2020 11:50:08 -0500 Received: from mail.kernel.org ([198.145.29.99]:54028 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405206AbgBNQUW (ORCPT ); Fri, 14 Feb 2020 11:20:22 -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 3C49024728; Fri, 14 Feb 2020 16:20:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581697222; bh=pNi86Qd8IpSJfMsjvwVOCG2Tki6Im0CYrxAz80yld8E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Zmdw9KXdn4+SB8iRrAhvpbyPgX3yVo+cYb8sbzLWvHusRMCINDQLivb+zejW+SZvw phKKAqS2VfEaAKZXyhzApOjx33mNEOP8OWHkv9jGYS3cCVhfFeaawQ1dd0Xm0OKHgB Rce5QfrvBBzXgUshXxoP6W6NnsRYApC0q7VIp+FU= 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 4.14 145/186] btrfs: safely advance counter when looking up bio csums Date: Fri, 14 Feb 2020 11:16:34 -0500 Message-Id: <20200214161715.18113-145-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200214161715.18113-1-sashal@kernel.org> References: <20200214161715.18113-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@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 fdcb410026233..2b994f7f820ec 100644 --- a/fs/btrfs/file-item.c +++ b/fs/btrfs/file-item.c @@ -288,7 +288,8 @@ 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