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ubifs: Handle re-linking of inodes correctly while recovery

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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: 474b93704f ("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>
Tested-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Richard Weinberger <richard@nod.at>
This commit is contained in:
Richard Weinberger 2018-11-07 23:04:43 +01:00
parent e542087701
commit e58725d51f
1 changed files with 37 additions and 0 deletions
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37
fs/ubifs/replay.c
View File

@ -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;
}