| Message ID | 20170518220249.GI4514@birch.djwong.org (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
On Thu, May 18, 2017 at 03:02:49PM -0700, Darrick J. Wong wrote: > 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> > --- > v3: fix the error exit paths always to free the list > v2: leave a comment discussing why we use an empty transaction > --- Reviewed-by: Brian Foster <bfoster@redhat.com> > fs/xfs/libxfs/xfs_refcount.c | 43 ++++++++++++++++++++++++++++++------------ > 1 file changed, 31 insertions(+), 12 deletions(-) > > diff --git a/fs/xfs/libxfs/xfs_refcount.c b/fs/xfs/libxfs/xfs_refcount.c > index b177ef3..82a38d8 100644 > --- a/fs/xfs/libxfs/xfs_refcount.c > +++ b/fs/xfs/libxfs/xfs_refcount.c > @@ -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 @@ 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_cancel(tp); > - goto out_free; > + xfs_trans_brelse(tp, agbp); > + goto out_trans; > } > > ----- End forwarded message ----- > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/xfs/libxfs/xfs_refcount.c b/fs/xfs/libxfs/xfs_refcount.c index b177ef3..82a38d8 100644 --- a/fs/xfs/libxfs/xfs_refcount.c +++ b/fs/xfs/libxfs/xfs_refcount.c @@ -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 @@ 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_cancel(tp); - goto out_free; + xfs_trans_brelse(tp, agbp); + goto out_trans; }
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> --- v3: fix the error exit paths always to free the list v2: leave a comment discussing why we use an empty transaction --- fs/xfs/libxfs/xfs_refcount.c | 43 ++++++++++++++++++++++++++++++------------ 1 file changed, 31 insertions(+), 12 deletions(-) ----- End forwarded message ----- -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html