[patch 091/114] jbd2: Avoid possible NULL dereference in jbd2_journal_begin_ordered_truncate()

Greg KH
2009-03-14T01:54:37Z

[-- Attachment #1: jbd2-avoid-possible-null-dereference-in-jbd2_journal_begin_ordered_truncate.patch --]
[-- Type: text/plain, Size: 5673 bytes --]

2.6.28-stable review patch. If anyone has any objections, please let us know.

------------------

From: Jan Kara <jack@suse.cz>

(cherry picked from commit 7f5aa215088b817add9c71914b83650bdd49f8a9)

If we race with commit code setting i_transaction to NULL, we could
possibly dereference it. Proper locking requires the journal pointer
(to access journal->j_list_lock), which we don't have. So we have to
change the prototype of the function so that filesystem passes us the
journal pointer. Also add a more detailed comment about why the
function jbd2_journal_begin_ordered_truncate() does what it does and
how it should be used.

Thanks to Dan Carpenter <error27@gmail.com> for pointing to the
suspitious code.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Acked-by: Joel Becker <joel.becker@oracle.com>
CC: linux-ext4@vger.kernel.org
CC: ocfs2-devel@oss.oracle.com
CC: mfasheh@suse.de
CC: Dan Carpenter <error27@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/ext4/inode.c | 6 ++++--
fs/jbd2/transaction.c | 42 +++++++++++++++++++++++++++++++-----------
fs/ocfs2/journal.h | 6 ++++--
include/linux/jbd2.h | 3 ++-
4 files changed, 41 insertions(+), 16 deletions(-)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -46,8 +46,10 @@
static inline int ext4_begin_ordered_truncate(struct inode *inode,
loff_t new_size)
{
- return jbd2_journal_begin_ordered_truncate(&EXT4_I(inode)->jinode,
- new_size);
+ return jbd2_journal_begin_ordered_truncate(
+ EXT4_SB(inode->i_sb)->s_journal,
+ &EXT4_I(inode)->jinode,
+ new_size);
}

static void ext4_invalidatepage(struct page *page, unsigned long offset);
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -2050,26 +2050,46 @@ done:
}

/*
- * This function must be called when inode is journaled in ordered mode
- * before truncation happens. It starts writeout of truncated part in
- * case it is in the committing transaction so that we stand to ordered
- * mode consistency guarantees.
+ * File truncate and transaction commit interact with each other in a
+ * non-trivial way. If a transaction writing data block A is
+ * committing, we cannot discard the data by truncate until we have
+ * written them. Otherwise if we crashed after the transaction with
+ * write has committed but before the transaction with truncate has
+ * committed, we could see stale data in block A. This function is a
+ * helper to solve this problem. It starts writeout of the truncated
+ * part in case it is in the committing transaction.
+ *
+ * Filesystem code must call this function when inode is journaled in
+ * ordered mode before truncation happens and after the inode has been
+ * placed on orphan list with the new inode size. The second condition
+ * avoids the race that someone writes new data and we start
+ * committing the transaction after this function has been called but
+ * before a transaction for truncate is started (and furthermore it
+ * allows us to optimize the case where the addition to orphan list
+ * happens in the same transaction as write --- we don't have to write
+ * any data in such case).
*/
-int jbd2_journal_begin_ordered_truncate(struct jbd2_inode *inode,
+int jbd2_journal_begin_ordered_truncate(journal_t *journal,
+ struct jbd2_inode *jinode,
loff_t new_size)
{
- journal_t *journal;
- transaction_t *commit_trans;
+ transaction_t *inode_trans, *commit_trans;
int ret = 0;

- if (!inode->i_transaction && !inode->i_next_transaction)
+ /* This is a quick check to avoid locking if not necessary */
+ if (!jinode->i_transaction)
goto out;
- journal = inode->i_transaction->t_journal;
+ /* Locks are here just to force reading of recent values, it is
+ * enough that the transaction was not committing before we started
+ * a transaction adding the inode to orphan list */
spin_lock(&journal->j_state_lock);
commit_trans = journal->j_committing_transaction;
spin_unlock(&journal->j_state_lock);
- if (inode->i_transaction == commit_trans) {
- ret = filemap_fdatawrite_range(inode->i_vfs_inode->i_mapping,
+ spin_lock(&journal->j_list_lock);
+ inode_trans = jinode->i_transaction;
+ spin_unlock(&journal->j_list_lock);
+ if (inode_trans == commit_trans) {
+ ret = filemap_fdatawrite_range(jinode->i_vfs_inode->i_mapping,
new_size, LLONG_MAX);
if (ret)
jbd2_journal_abort(journal, ret);
--- a/fs/ocfs2/journal.h
+++ b/fs/ocfs2/journal.h
@@ -445,8 +445,10 @@ static inline int ocfs2_jbd2_file_inode(
static inline int ocfs2_begin_ordered_truncate(struct inode *inode,
loff_t new_size)
{
- return jbd2_journal_begin_ordered_truncate(&OCFS2_I(inode)->ip_jinode,
- new_size);
+ return jbd2_journal_begin_ordered_truncate(
+ OCFS2_SB(inode->i_sb)->journal->j_journal,
+ &OCFS2_I(inode)->ip_jinode,
+ new_size);
}

#endif /* OCFS2_JOURNAL_H */
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -1087,7 +1087,8 @@ extern int jbd2_journal_clear_err (j
extern int jbd2_journal_bmap(journal_t *, unsigned long, unsigned long long *);
extern int jbd2_journal_force_commit(journal_t *);
extern int jbd2_journal_file_inode(handle_t *handle, struct jbd2_inode *inode);
-extern int jbd2_journal_begin_ordered_truncate(struct jbd2_inode *inode, loff_t new_size);
+extern int jbd2_journal_begin_ordered_truncate(journal_t *journal,
+ struct jbd2_inode *inode, loff_t new_size);
extern void jbd2_journal_init_jbd_inode(struct jbd2_inode *jinode, struct inode *inode);
extern void jbd2_journal_release_jbd_inode(journal_t *journal, struct jbd2_inode *jinode);