Re: [PATCH 2/4] xfs: abort dir/attr btree operation if btree is obviously weird

Darrick J. Wong
2017-10-26T16:54:35Z

On Thu, Oct 26, 2017 at 09:16:44AM -0400, Brian Foster wrote:
> On Wed, Oct 25, 2017 at 10:49:30PM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> >
> > Abort an dir/attr btree operation if the attr btree has obvious problems
> > like loops back to the root or pointers don't point down the tree.
> > Found by fuzzing btree[0].before to zero in xfs/402, which livelocks on
> > the cycle in the attr btree.
> >
> > Apply the same checks to xfs_da3_node_lookup_int.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> > fs/xfs/libxfs/xfs_da_btree.c | 34 +++++++++++++++++++++++++++++++++-
> > fs/xfs/xfs_attr_list.c | 32 ++++++++++++++++++++++++++++++++
> > 2 files changed, 65 insertions(+), 1 deletion(-)
> >
> >
> > diff --git a/fs/xfs/libxfs/xfs_da_btree.c b/fs/xfs/libxfs/xfs_da_btree.c
> > index 6d43358..3dbeda6 100644
> > --- a/fs/xfs/libxfs/xfs_da_btree.c
> > +++ b/fs/xfs/libxfs/xfs_da_btree.c
> > @@ -1466,6 +1466,7 @@ xfs_da3_node_lookup_int(
> > int max;
> > int error;
> > int retval;
> > + unsigned int expected_level = -1U;
> > struct xfs_inode *dp = state->args->dp;
> >
> > args = state->args;
> > @@ -1474,7 +1475,7 @@ xfs_da3_node_lookup_int(
> > * Descend thru the B-tree searching each level for the right
> > * node to use, until the right hashval is found.
> > */
> > - blkno = (args->whichfork == XFS_DATA_FORK)? args->geo->leafblk : 0;
> > + blkno = args->geo->leafblk;
> > for (blk = &state->path.blk[0], state->path.active = 1;
> > state->path.active <= XFS_DA_NODE_MAXDEPTH;
> > blk++, state->path.active++) {
> > @@ -1496,6 +1497,8 @@ xfs_da3_node_lookup_int(
> > blk->magic == XFS_ATTR3_LEAF_MAGIC) {
> > blk->magic = XFS_ATTR_LEAF_MAGIC;
> > blk->hashval = xfs_attr_leaf_lasthash(blk->bp, NULL);
> > + if (expected_level == -1U)
> > + expected_level = 0;
>
> Now that these functions check that expected_level reaches 0, it seems
> like we could just initialize it to 0 and eliminate these
> checks/assignments..? I think that may also help catch the case a single
> node block with an invalid level == 0.

Hmm, you're right, it's fine to initialize it to zero since there's no
way we fail to iterate the loop at least once.

> > break;
> > }
> >
> > @@ -1504,6 +1507,8 @@ xfs_da3_node_lookup_int(
> > blk->magic = XFS_DIR2_LEAFN_MAGIC;
> > blk->hashval = xfs_dir2_leaf_lasthash(args->dp,
> > blk->bp, NULL);
> > + if (expected_level == -1U)
> > + expected_level = 0;
> > break;
> > }
> >
> > @@ -1517,6 +1522,26 @@ xfs_da3_node_lookup_int(
> > dp->d_ops->node_hdr_from_disk(&nodehdr, node);
> > btree = dp->d_ops->node_tree_p(node);
> >
> > + /* Tree taller than we can handle; bail out! */
> > + if (nodehdr.level >= XFS_DA_NODE_MAXDEPTH)
> > + return -EFSCORRUPTED;
> > +
> > + if (blkno == args->geo->leafblk) {
> > + /*
> > + * This is the root node, set up for the
> > + * next level we want to see.
> > + */
> > + expected_level = nodehdr.level - 1;
> > + } else if (expected_level != nodehdr.level) {
> > + /*
> > + * Not the level we were expecting, which
> > + * implies that the tree is bad.
> > + */
> > + return -EFSCORRUPTED;
> > + } else {
> > + expected_level--;
> > + }
> > +
>
> And just an aesthetic nit that these stanzas could probably be made a
> little easier to read:
>
> /*
> * Track the level from the root node ...
> */
> if (blk == args->geo->leafblk)
> expected_level = nodehdr.level - 1;
> else if (expected_level != nodehdr.level)
> return -EFSCORRUPTED;
> else
> expected_level--;
>
> Otherwise looks Ok.

Ok.

--D

>
> Brian
>
> > max = nodehdr.count;
> > blk->hashval = be32_to_cpu(btree[max - 1].hashval);
> >
> > @@ -1562,8 +1587,15 @@ xfs_da3_node_lookup_int(
> > blk->index = probe;
> > blkno = be32_to_cpu(btree[probe].before);
> > }
> > +
> > + /* We can't point back to the root. */
> > + if (blkno == args->geo->leafblk)
> > + return -EFSCORRUPTED;
> > }
> >
> > + if (expected_level != 0)
> > + return -EFSCORRUPTED;
> > +
> > /*
> > * A leaf block that ends in the hashval that we are interested in
> > * (final hashval == search hashval) means that the next block may
> > diff --git a/fs/xfs/xfs_attr_list.c b/fs/xfs/xfs_attr_list.c
> > index 48423eb..9a8dafc 100644
> > --- a/fs/xfs/xfs_attr_list.c
> > +++ b/fs/xfs/xfs_attr_list.c
> > @@ -222,6 +222,7 @@ xfs_attr_node_list_lookup(
> > struct xfs_trans *tp = context->tp;
> > int i;
> > int error = 0;
> > + unsigned int expected_level = -1U;
> > uint16_t magic;
> >
> > ASSERT(*pbp == NULL);
> > @@ -236,6 +237,8 @@ xfs_attr_node_list_lookup(
> > switch (magic) {
> > case XFS_ATTR_LEAF_MAGIC:
> > case XFS_ATTR3_LEAF_MAGIC:
> > + if (expected_level == -1U)
> > + expected_level = 0;
> > goto found_leaf;
> > case XFS_DA_NODE_MAGIC:
> > case XFS_DA3_NODE_MAGIC:
> > @@ -249,6 +252,26 @@ xfs_attr_node_list_lookup(
> >
> > dp->d_ops->node_hdr_from_disk(&nodehdr, node);
> >
> > + /* Tree taller than we can handle; bail out! */
> > + if (nodehdr.level >= XFS_DA_NODE_MAXDEPTH)
> > + goto out_corruptbuf;
> > +
> > + if (cursor->blkno == 0) {
> > + /*
> > + * This is the root node, set up for the
> > + * next level we want to see.
> > + */
> > + expected_level = nodehdr.level - 1;
> > + } else if (expected_level != nodehdr.level) {
> > + /*
> > + * Not the level we were expecting, which
> > + * implies that the tree is bad.
> > + */
> > + goto out_corruptbuf;
> > + } else {
> > + expected_level--;
> > + }
> > +
> > btree = dp->d_ops->node_tree_p(node);
> > for (i = 0; i < nodehdr.count; btree++, i++) {
> > if (cursor->hashval <= be32_to_cpu(btree->hashval)) {
> > @@ -262,15 +285,24 @@ xfs_attr_node_list_lookup(
> > goto out_buf;
> >
> > xfs_trans_brelse(tp, *pbp);
> > +
> > + /* We can't point back to the root. */
> > + if (cursor->blkno == 0) {
> > + error = -EFSCORRUPTED;
> > + goto out;
> > + }
> > }
> >
> > found_leaf:
> > + if (expected_level != 0)
> > + goto out_corruptbuf;
> > return error;
> >
> > out_corruptbuf:
> > error = -EFSCORRUPTED;
> > out_buf:
> > xfs_trans_brelse(tp, *pbp);
> > +out:
> > *pbp = NULL;
> > return error;
> > }
> >
> > --
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