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 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 Signed-off-by: Richard Weinberger richard@nod.at --- fs/ubifs/replay.c | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+)

diff --git a/fs/ubifs/replay.c b/fs/ubifs/replay.c index 75f961c4c044..cb1f23459553 100644 --- a/fs/ubifs/replay.c +++ b/fs/ubifs/replay.c @@ -212,6 +212,38 @@ 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(c, rino->deletion); + ubifs_assert(c, 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(c, r->sqnum >= rino->sqnum); + if (key_inum(c, &r->key) == key_inum(c, &rino->key)) + return r->deletion == 0; + + } + + ubifs_assert(c, 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; }