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xfs: avoid mount-time deadlock in CoW extent recovery

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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 <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
This commit is contained in:
Darrick J. Wong 2017-05-15 19:16:15 -07:00
parent ea9a46e1c4
commit 3ecb3ac7b9
1 changed files with 31 additions and 12 deletions
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43
fs/xfs/libxfs/xfs_refcount.c
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@ -1629,13 +1629,28 @@ 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);
INIT_LIST_HEAD(&debris);
/*
* 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);
memset(&low, 0, sizeof(low));
memset(&high, 0, sizeof(high));
low.rc.rc_startblock = XFS_REFC_COW_START;
@ -1645,10 +1660,11 @@ 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 +1692,16 @@ 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);
out_trans:
xfs_trans_cancel(tp);
out_free:
/* Free the leftover list */
list_for_each_entry_safe(rr, n, &debris, rr_list) {
@ -1688,11 +1712,6 @@ out_free:
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_cancel(tp);
goto out_free;
xfs_trans_brelse(tp, agbp);
goto out_trans;
}