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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2A84CC433F5 for ; Tue, 24 May 2022 19:50:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241026AbiEXTuM (ORCPT ); Tue, 24 May 2022 15:50:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33136 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241024AbiEXTuL (ORCPT ); Tue, 24 May 2022 15:50:11 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 96CB779391 for ; Tue, 24 May 2022 12:50:10 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 55914B81B9A for ; Tue, 24 May 2022 19:50:09 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1C382C34100; Tue, 24 May 2022 19:50:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1653421808; bh=bcJ77HFb+92D2bKQBAuYNSecE2qLqDAwEO+V3iW0Ebg=; h=Date:From:To:Cc:Subject:From; b=PUhDVuRpch89CB17XhFxsPKrEcGuhfjR3KNO63kssaecDqxpyO0iEeb+DDjYYSaBX mfppgpJZnLwr5olatCzrP1fAJeepSxmF6X+XE3BksLs8jxt8sf4/QzIhL2PsyUNizD LTcVIJuyE8FvDQRf4oXa4YwglpZU0CgjSjgFfVqIwFdMy50qtxEGmkRi0TeP2z2q3f iFl5E9fF2OxzqtUymNK7JwNmUTqHid0RVr2doi5NlYdUY3/bwjFhrJg8Ys5IulnSko uw2wW2LbseHXSmY0IWhy4Xy++T/buHJp6MVgNwB7ZzXmX/mILrbfH2Bd6xDQToMU7X tLDrC20pJCr2w== Date: Tue, 24 May 2022 12:50:07 -0700 From: "Darrick J. Wong" To: Eric Sandeen Cc: xfs Subject: [PATCH] xfs_copy: don't use cached buffer reads until after libxfs_mount Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org From: Darrick J. Wong I accidentally tried to xfs_copy an ext4 filesystem, but instead of rejecting the filesystem, the program instead crashed. I figured out that zeroing the superblock was enough to trigger this: # dd if=/dev/zero of=/dev/sda bs=1024k count=1 # xfs_copy /dev/sda /dev/sdb Floating point exception The exact crash happens in this line from libxfs_getbuf_flags, which is called from the main() routine of xfs_copy: if (btp == btp->bt_mount->m_ddev_targp) { (*bpp)->b_pag = xfs_perag_get(btp->bt_mount, xfs_daddr_to_agno(btp->bt_mount, blkno)); The problem here is that the uncached read filled the incore superblock with zeroes, which means mbuf.sb_agblocks is zero. This causes a division by zero in xfs_daddr_to_agno, thereby crashing the program. In commit f8b581d6, we made it so that xfs_buf structures contain a passive reference to the associated perag structure. That commit assumes that no program would try a cached buffer read until the buffer cache is fully set up, which is true throughout xfsprogs... except for the beginning of xfs_copy. For whatever reason, it attempts an uncached read of the superblock to figure out the real superblock size, then performs a *cached* read with the proper buffer length and verifier. The cached read crashes the program. Fix the problem by changing the (second) cached read into an uncached read. Fixes: f8b581d6 ("libxfs: actually make buffers track the per-ag structures") Signed-off-by: Darrick J. Wong --- copy/xfs_copy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/copy/xfs_copy.c b/copy/xfs_copy.c index 41f594bd..79f65946 100644 --- a/copy/xfs_copy.c +++ b/copy/xfs_copy.c @@ -748,7 +748,7 @@ main(int argc, char **argv) /* Do it again, now with proper length and verifier */ libxfs_buf_relse(sbp); - error = -libxfs_buf_read(mbuf.m_ddev_targp, XFS_SB_DADDR, + error = -libxfs_buf_read_uncached(mbuf.m_ddev_targp, XFS_SB_DADDR, 1 << (sb->sb_sectlog - BBSHIFT), 0, &sbp, &xfs_sb_buf_ops); if (error) {