UBIFS: fix double free of ubifs_orphan objects

commit 8afd500c upstream.

The last orphan in the dnext list has its dnext set to NULL. Because
of that, ubifs_delete_orphan assumes that it is not on the dnext list
and frees it immediately instead ignoring it as a second delete. The
orphan is later freed again by erase_deleted.

This change adds an explicit flag to ubifs_orphan indicating whether
it is pending delete.
Signed-off-by: Adam Thomas <adamthomas1111@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Rui Xiang <rui.xiang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/ubifs/orphan.c

@@ -130,13 +130,14 @@ void ubifs_delete_orphan(struct ubifs_info *c, ino_t inum)
 		else if (inum > o->inum)
 			p = p->rb_right;
 		else {
-			if (o->dnext) {
+			if (o->del) {
 				spin_unlock(&c->orphan_lock);
 				dbg_gen("deleted twice ino %lu",
 					(unsigned long)inum);
 				return;
 			}
 			if (o->cnext) {
+				o->del = 1;
 				o->dnext = c->orph_dnext;
 				c->orph_dnext = o;
 				spin_unlock(&c->orphan_lock);
@@ -447,6 +448,7 @@ static void erase_deleted(struct ubifs_info *c)
 		orphan = dnext;
 		dnext = orphan->dnext;
 		ubifs_assert(!orphan->new);
+		ubifs_assert(orphan->del);
 		rb_erase(&orphan->rb, &c->orph_tree);
 		list_del(&orphan->list);
 		c->tot_orphans -= 1;
@@ -536,6 +538,7 @@ static int insert_dead_orphan(struct ubifs_info *c, ino_t inum)
 	rb_link_node(&orphan->rb, parent, p);
 	rb_insert_color(&orphan->rb, &c->orph_tree);
 	list_add_tail(&orphan->list, &c->orph_list);
+	orphan->del = 1;
 	orphan->dnext = c->orph_dnext;
 	c->orph_dnext = orphan;
 	dbg_mnt("ino %lu, new %d, tot %d", (unsigned long)inum,

fs/ubifs/ubifs.h

@@ -905,6 +905,7 @@ struct ubifs_budget_req {
  * @dnext: next orphan to delete
  * @inum: inode number
  * @new: %1 => added since the last commit, otherwise %0
+ * @del: %1 => delete pending, otherwise %0
  */
 struct ubifs_orphan {
 	struct rb_node rb;
@@ -914,6 +915,7 @@ struct ubifs_orphan {
 	struct ubifs_orphan *dnext;
 	ino_t inum;
 	int new;
+	unsigned del:1;
 };
 
 /**