[PATCH 4.9-4.19] jbd2: fix use-after-free of transaction_t race

[Samuel Mendoza-Jonas <samjonas@amazon.com>]

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>
[backport to 4.9-4.19 in original jbd2_journal_commit_transaction()
 location before the refactor in
 4f9818684870 "jbd2: refactor wait logic for transaction updates into a
 common function"]
Signed-off-by: Samuel Mendoza-Jonas <samjonas@amazon.com>
Fixes: 1da177e4c3f41524
Cc: stable@kernel.org # 4.9.x - 4.19.x
---
While marked for 5.17 stable, it looks like this fix also applies to the
original location in jbd2_journal_commit_transaction() before it was
refactored to use jbd2_journal_wait_updates(). This applies the same
change there.

 fs/jbd2/commit.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 97760cb9bcd7..66e776eb5ea7 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -382,6 +382,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 	int csum_size = 0;
 	LIST_HEAD(io_bufs);
 	LIST_HEAD(log_bufs);
+	DEFINE_WAIT(wait);
 
 	if (jbd2_journal_has_csum_v2or3(journal))
 		csum_size = sizeof(struct jbd2_journal_block_tail);
@@ -434,22 +435,25 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 	stats.run.rs_running = jbd2_time_diff(commit_transaction->t_start,
 					      stats.run.rs_locked);
 
-	spin_lock(&commit_transaction->t_handle_lock);
-	while (atomic_read(&commit_transaction->t_updates)) {
-		DEFINE_WAIT(wait);
+	while (1) {
+		commit_transaction = journal->j_running_transaction;
+		if (!commit_transaction)
+			break;
 
+		spin_lock(&commit_transaction->t_handle_lock);
 		prepare_to_wait(&journal->j_wait_updates, &wait,
 					TASK_UNINTERRUPTIBLE);
-		if (atomic_read(&commit_transaction->t_updates)) {
+		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);
+			finish_wait(&journal->j_wait_updates, &wait);
+			break;
 		}
+		spin_unlock(&commit_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);
 
 	J_ASSERT (atomic_read(&commit_transaction->t_outstanding_credits) <=
 			journal->j_max_transaction_buffers);
-- 
2.25.1