From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp1040.oracle.com ([141.146.126.69]:32644 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751845AbdEQBHh (ORCPT ); Tue, 16 May 2017 21:07:37 -0400 Date: Tue, 16 May 2017 18:07:28 -0700 From: "Darrick J. Wong" Subject: [PATCH v2] xfs: avoid mount-time deadlock in CoW extent recovery Message-ID: <20170517010728.GS4519@birch.djwong.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: xfs Cc: Dave Chinner If a malicious user corrupts the refcount btree to cause a cycle between different levels of the tree, the next mount attempt will deadlock in the CoW recovery routine while grabbing buffer locks. We can use the ability to re-grab a buffer that was previous locked to a transaction to avoid deadlocks, so do that here. Signed-off-by: Darrick J. Wong --- v2: leave a comment discussing why we use an empty transaction --- fs/xfs/libxfs/xfs_refcount.c | 39 +++++++++++++++++++++++++++++---------- 1 file changed, 29 insertions(+), 10 deletions(-) diff --git a/fs/xfs/libxfs/xfs_refcount.c b/fs/xfs/libxfs/xfs_refcount.c index b177ef3..3d2b29b 100644 --- a/fs/xfs/libxfs/xfs_refcount.c +++ b/fs/xfs/libxfs/xfs_refcount.c @@ -1629,10 +1629,24 @@ xfs_refcount_recover_cow_leftovers( if (mp->m_sb.sb_agblocks >= XFS_REFC_COW_START) return -EOPNOTSUPP; - error = xfs_alloc_read_agf(mp, NULL, agno, 0, &agbp); + /* + * In this first part, we use an empty transaction to gather up + * all the leftover CoW extents so that we can subsequently + * delete them. The empty transaction is used to avoid + * a buffer lock deadlock if there happens to be a loop in the + * refcountbt because we're allowed to re-grab a buffer that is + * already attached to our transaction. When we're done + * recording the CoW debris we cancel the (empty) transaction + * and everything goes away cleanly. + */ + error = xfs_trans_alloc_empty(mp, &tp); if (error) return error; - cur = xfs_refcountbt_init_cursor(mp, NULL, agbp, agno, NULL); + + error = xfs_alloc_read_agf(mp, tp, agno, 0, &agbp); + if (error) + goto out_trans; + cur = xfs_refcountbt_init_cursor(mp, tp, agbp, agno, NULL); /* Find all the leftover CoW staging extents. */ INIT_LIST_HEAD(&debris); @@ -1645,10 +1659,11 @@ xfs_refcount_recover_cow_leftovers( if (error) goto out_cursor; xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR); - xfs_buf_relse(agbp); + xfs_trans_brelse(tp, agbp); + xfs_trans_cancel(tp); /* Now iterate the list to free the leftovers */ - list_for_each_entry(rr, &debris, rr_list) { + list_for_each_entry_safe(rr, n, &debris, rr_list) { /* Set up transaction. */ error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, 0, 0, 0, &tp); if (error) @@ -1676,8 +1691,15 @@ xfs_refcount_recover_cow_leftovers( error = xfs_trans_commit(tp); if (error) goto out_free; + + list_del(&rr->rr_list); + kmem_free(rr); } + return error; +out_defer: + xfs_defer_cancel(&dfops); + xfs_trans_cancel(tp); out_free: /* Free the leftover list */ list_for_each_entry_safe(rr, n, &debris, rr_list) { @@ -1688,11 +1710,8 @@ xfs_refcount_recover_cow_leftovers( out_cursor: xfs_btree_del_cursor(cur, XFS_BTREE_ERROR); - xfs_buf_relse(agbp); - goto out_free; - -out_defer: - xfs_defer_cancel(&dfops); + xfs_trans_brelse(tp, agbp); +out_trans: xfs_trans_cancel(tp); - goto out_free; + return error; }