ubifs: Handle re-linking of inodes correctly while recovery

commit e58725d51fa8da9133f3f1c54170aa2e43056b91 upstream.

UBIFS's recovery code strictly assumes that a deleted inode will never
come back, therefore it removes all data which belongs to that inode
as soon it faces an inode with link count 0 in the replay list.
Before O_TMPFILE this assumption was perfectly fine. With O_TMPFILE
it can lead to data loss upon a power-cut.

Consider a journal with entries like:
0: inode X (nlink = 0) /* O_TMPFILE was created */
1: data for inode X /* Someone writes to the temp file */
2: inode X (nlink = 0) /* inode was changed, xattr, chmod, … */
3: inode X (nlink = 1) /* inode was re-linked via linkat() */

Upon replay of entry #2 UBIFS will drop all data that belongs to inode X,
this will lead to an empty file after mounting.

As solution for this problem, scan the replay list for a re-link entry
before dropping data.

Fixes: 474b93704f32 ("ubifs: Implement O_TMPFILE")
Cc: stable@vger.kernel.org # 4.9-4.18
Cc: Russell Senior <russell@personaltelco.net>
Cc: Rafał Miłecki <zajec5@gmail.com>
Reported-by: Russell Senior <russell@personaltelco.net>
Reported-by: Rafał Miłecki <zajec5@gmail.com>
Tested-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Richard Weinberger <richard@nod.at>
[rmilecki: update ubifs_assert() calls to compile with 4.18 and older]
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
(cherry picked from commit e58725d51fa8da9133f3f1c54170aa2e43056b91)
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/ubifs/replay.c b/fs/ubifs/replay.c
index ae5c02f22f3e7ded6545fe52859abef20742d9d7..d998fbf7de3081ce2d91e2bb4a0d631787bdb9b1 100644 (file)
--- a/fs/ubifs/replay.c
+++ b/fs/ubifs/replay.c
@@ -209,6 +209,38 @@ static int trun_remove_range(struct ubifs_info *c, struct replay_entry *r)
        return ubifs_tnc_remove_range(c, &min_key, &max_key);
 }
 
+/**
+ * inode_still_linked - check whether inode in question will be re-linked.
+ * @c: UBIFS file-system description object
+ * @rino: replay entry to test
+ *
+ * O_TMPFILE files can be re-linked, this means link count goes from 0 to 1.
+ * This case needs special care, otherwise all references to the inode will
+ * be removed upon the first replay entry of an inode with link count 0
+ * is found.
+ */
+static bool inode_still_linked(struct ubifs_info *c, struct replay_entry *rino)
+{
+       struct replay_entry *r;
+
+       ubifs_assert(rino->deletion);
+       ubifs_assert(key_type(c, &rino->key) == UBIFS_INO_KEY);
+
+       /*
+        * Find the most recent entry for the inode behind @rino and check
+        * whether it is a deletion.
+        */
+       list_for_each_entry_reverse(r, &c->replay_list, list) {
+               ubifs_assert(r->sqnum >= rino->sqnum);
+               if (key_inum(c, &r->key) == key_inum(c, &rino->key))
+                       return r->deletion == 0;
+
+       }
+
+       ubifs_assert(0);
+       return false;
+}
+
 /**
  * apply_replay_entry - apply a replay entry to the TNC.
  * @c: UBIFS file-system description object
@@ -239,6 +271,11 @@ static int apply_replay_entry(struct ubifs_info *c, struct replay_entry *r)
                        {
                                ino_t inum = key_inum(c, &r->key);
 
+                               if (inode_still_linked(c, r)) {
+                                       err = 0;
+                                       break;
+                               }
+
                                err = ubifs_tnc_remove_ino(c, inum);
                                break;
                        }