[PATCH 5.17 31/39] jbd2: fix use-after-free of transaction_t race

Greg Kroah-Hartman
2022-03-25T15:30:19Z

From: Ritesh Harjani <riteshh@linux.ibm.com>

commit cc16eecae687912238ee6efbff71ad31e2bc414e upstream.

jbd2_journal_wait_updates() is called with j_state_lock held. But if
there is a commit in progress, then this transaction might get committed
and freed via jbd2_journal_commit_transaction() ->
jbd2_journal_free_transaction(), when we release j_state_lock.
So check for journal->j_running_transaction everytime we release and
acquire j_state_lock to avoid use-after-free issue.

Link: https://lore.kernel.org/r/948c2fed518ae739db6a8f7f83f1d58b504f87d0.1644497105.git.ritesh.list@gmail.com
Fixes: 4f98186848707f53 ("jbd2: refactor wait logic for transaction updates into a common function")
Cc: stable@kernel.org
Reported-and-tested-by: syzbot+afa2ca5171d93e44b348@syzkaller.appspotmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/jbd2/transaction.c | 41 +++++++++++++++++++++++++----------------
1 file changed, 25 insertions(+), 16 deletions(-)

--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -842,27 +842,38 @@ EXPORT_SYMBOL(jbd2_journal_restart);
*/
void jbd2_journal_wait_updates(journal_t *journal)
{
- transaction_t *commit_transaction = journal->j_running_transaction;
+ DEFINE_WAIT(wait);

- if (!commit_transaction)
- return;
+ while (1) {
+ /*
+ * Note that the running transaction can get freed under us if
+ * this transaction is getting committed in
+ * jbd2_journal_commit_transaction() ->
+ * jbd2_journal_free_transaction(). This can only happen when we
+ * release j_state_lock -> schedule() -> acquire j_state_lock.
+ * Hence we should everytime retrieve new j_running_transaction
+ * value (after j_state_lock release acquire cycle), else it may
+ * lead to use-after-free of old freed transaction.
+ */
+ transaction_t *transaction = journal->j_running_transaction;

- spin_lock(&commit_transaction->t_handle_lock);
- while (atomic_read(&commit_transaction->t_updates)) {
- DEFINE_WAIT(wait);
+ if (!transaction)
+ break;

+ spin_lock(&transaction->t_handle_lock);
prepare_to_wait(&journal->j_wait_updates, &wait,
- TASK_UNINTERRUPTIBLE);
- if (atomic_read(&commit_transaction->t_updates)) {
- spin_unlock(&commit_transaction->t_handle_lock);
- write_unlock(&journal->j_state_lock);
- schedule();
- write_lock(&journal->j_state_lock);
- spin_lock(&commit_transaction->t_handle_lock);
+ TASK_UNINTERRUPTIBLE);
+ if (!atomic_read(&transaction->t_updates)) {
+ spin_unlock(&transaction->t_handle_lock);
+ finish_wait(&journal->j_wait_updates, &wait);
+ break;
}
+ spin_unlock(&transaction->t_handle_lock);
+ write_unlock(&journal->j_state_lock);
+ schedule();
finish_wait(&journal->j_wait_updates, &wait);
+ write_lock(&journal->j_state_lock);
}
- spin_unlock(&commit_transaction->t_handle_lock);
}

/**
@@ -877,8 +888,6 @@ void jbd2_journal_wait_updates(journal_t
*/
void jbd2_journal_lock_updates(journal_t *journal)
{
- DEFINE_WAIT(wait);
-
jbd2_might_wait_for_commit(journal);

write_lock(&journal->j_state_lock);