xfs: reserve quota for dir expansion when linking/unlinking files

[ Upstream commit 871b9316e7a778ff97bdc34fdb2f2977f616651d ]

XFS does not reserve quota for directory expansion when linking or
unlinking children from a directory.  This means that we don't reject
the expansion with EDQUOT when we're at or near a hard limit, which
means that unprivileged userspace can use link()/unlink() to exceed
quota.

The fix for this is nuanced -- link operations don't always expand the
directory, and we allow a link to proceed with no space reservation if
we don't need to add a block to the directory to handle the addition.
Unlink operations generally do not expand the directory (you'd have to
free a block and then cause a btree split) and we can defer the
directory block freeing if there is no space reservation.

Moreover, there is a further bug in that we do not trigger the blockgc
workers to try to clear space when we're out of quota.

To fix both cases, create a new xfs_trans_alloc_dir function that
allocates the transaction, locks and joins the inodes, and reserves
quota for the directory.  If there isn't sufficient space or quota,
we'll switch the caller to reservationless mode.  This should prevent
quota usage overruns with the least restriction in functionality.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Leah Rumancik <leah.rumancik@gmail.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 86 insertions, 0 deletions

diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 67dec11e34c7..95c183072e7a 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -1201,3 +1201,89 @@ out_cancel:
 	xfs_trans_cancel(tp);
 	return error;
 }
+
+/*
+ * Allocate an transaction, lock and join the directory and child inodes to it,
+ * and reserve quota for a directory update.  If there isn't sufficient space,
+ * @dblocks will be set to zero for a reservationless directory update and
+ * @nospace_error will be set to a negative errno describing the space
+ * constraint we hit.
+ *
+ * The caller must ensure that the on-disk dquots attached to this inode have
+ * already been allocated and initialized.  The ILOCKs will be dropped when the
+ * transaction is committed or cancelled.
+ */
+int
+xfs_trans_alloc_dir(
+	struct xfs_inode	*dp,
+	struct xfs_trans_res	*resv,
+	struct xfs_inode	*ip,
+	unsigned int		*dblocks,
+	struct xfs_trans	**tpp,
+	int			*nospace_error)
+{
+	struct xfs_trans	*tp;
+	struct xfs_mount	*mp = ip->i_mount;
+	unsigned int		resblks;
+	bool			retried = false;
+	int			error;
+
+retry:
+	*nospace_error = 0;
+	resblks = *dblocks;
+	error = xfs_trans_alloc(mp, resv, resblks, 0, 0, &tp);
+	if (error == -ENOSPC) {
+		*nospace_error = error;
+		resblks = 0;
+		error = xfs_trans_alloc(mp, resv, resblks, 0, 0, &tp);
+	}
+	if (error)
+		return error;
+
+	xfs_lock_two_inodes(dp, XFS_ILOCK_EXCL, ip, XFS_ILOCK_EXCL);
+
+	xfs_trans_ijoin(tp, dp, XFS_ILOCK_EXCL);
+	xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
+
+	error = xfs_qm_dqattach_locked(dp, false);
+	if (error) {
+		/* Caller should have allocated the dquots! */
+		ASSERT(error != -ENOENT);
+		goto out_cancel;
+	}
+
+	error = xfs_qm_dqattach_locked(ip, false);
+	if (error) {
+		/* Caller should have allocated the dquots! */
+		ASSERT(error != -ENOENT);
+		goto out_cancel;
+	}
+
+	if (resblks == 0)
+		goto done;
+
+	error = xfs_trans_reserve_quota_nblks(tp, dp, resblks, 0, false);
+	if (error == -EDQUOT || error == -ENOSPC) {
+		if (!retried) {
+			xfs_trans_cancel(tp);
+			xfs_blockgc_free_quota(dp, 0);
+			retried = true;
+			goto retry;
+		}
+
+		*nospace_error = error;
+		resblks = 0;
+		error = 0;
+	}
+	if (error)
+		goto out_cancel;
+
+done:
+	*tpp = tp;
+	*dblocks = resblks;
+	return 0;
+
+out_cancel:
+	xfs_trans_cancel(tp);
+	return error;
+}