ubifs: Check link count of inodes when killing orphans.

O_TMPFILE files can change their link count back to non-zero.
This corner case needs to get addressed in the orphans subsystem
too.

Fixes: 474b937 ("ubifs: Implement O_TMPFILE")
Reported-by: Lars Persson <lists@bofh.nu>
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/orphan.c

@@ -630,6 +630,7 @@ static int do_kill_orphans(struct ubifs_info *c, struct ubifs_scan_leb *sleb,
 {
 	struct ubifs_scan_node *snod;
 	struct ubifs_orph_node *orph;
+	struct ubifs_ino_node *ino = NULL;
 	unsigned long long cmt_no;
 	ino_t inum;
 	int i, n, err, first = 1;
@@ -676,23 +677,40 @@ static int do_kill_orphans(struct ubifs_info *c, struct ubifs_scan_leb *sleb,
 		if (first)
 			first = 0;
 
+		ino = kmalloc(UBIFS_MAX_INO_NODE_SZ, GFP_NOFS);
+		if (!ino)
+			return -ENOMEM;
+
 		n = (le32_to_cpu(orph->ch.len) - UBIFS_ORPH_NODE_SZ) >> 3;
 		for (i = 0; i < n; i++) {
 			union ubifs_key key1, key2;
 
 			inum = le64_to_cpu(orph->inos[i]);
-			dbg_rcvry("deleting orphaned inode %lu",
-				  (unsigned long)inum);
-
-			lowest_ino_key(c, &key1, inum);
-			highest_ino_key(c, &key2, inum);
 
-			err = ubifs_tnc_remove_range(c, &key1, &key2);
+			ino_key_init(c, &key1, inum);
+			err = ubifs_tnc_lookup(c, &key1, ino);
 			if (err)
-				return err;
+				goto out_free;
+
+			/*
+			 * Check whether an inode can really get deleted.
+			 * linkat() with O_TMPFILE allows rebirth of an inode.
+			 */
+			if (ino->nlink == 0) {
+				dbg_rcvry("deleting orphaned inode %lu",
+					  (unsigned long)inum);
+
+				lowest_ino_key(c, &key1, inum);
+				highest_ino_key(c, &key2, inum);
+
+				err = ubifs_tnc_remove_range(c, &key1, &key2);
+				if (err)
+					goto out_ro;
+			}
+
 			err = insert_dead_orphan(c, inum);
 			if (err)
-				return err;
+				goto out_free;
 		}
 
 		*last_cmt_no = cmt_no;
@@ -704,7 +722,15 @@ static int do_kill_orphans(struct ubifs_info *c, struct ubifs_scan_leb *sleb,
 			*last_flagged = 0;
 	}
 
-	return 0;
+	err = 0;
+out_free:
+	kfree(ino);
+	return err;
+
+out_ro:
+	ubifs_ro_mode(c, err);
+	kfree(ino);
+	return err;
 }
 
 /**