quota: paranoia: check quota tree root

Root level in quota tree must be already allocated otherwise this block
could be used for something else.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 7 insertions, 0 deletions

diff --git a/fs/quota/quota_tree.c b/fs/quota/quota_tree.c
index d65877fbe8f4..58efb83dec1c 100644
--- a/fs/quota/quota_tree.c
+++ b/fs/quota/quota_tree.c
@@ -349,6 +349,13 @@ static inline int dq_insert_tree(struct qtree_mem_dqinfo *info,
                                  struct dquot *dquot)
 {
         int tmp = QT_TREEOFF;
+
+#ifdef __QUOTA_QT_PARANOIA
+        if (info->dqi_blocks <= QT_TREEOFF) {
+                quota_error(dquot->dq_sb, "Quota tree root isn't allocated!");
+                return -EIO;
+        }
+#endif
         return do_insert_tree(info, dquot, &tmp, 0);
 }