int jbd2_journal_get_undo_access(handle_t *handle, struct buffer_head *bh)
{
	int err;
	struct journal_head *jh = jbd2_journal_add_journal_head(bh);
	char *committed_data = NULL;

	JBUFFER_TRACE(jh, "entry");

	/*
	 * Do this first --- it can drop the journal lock, so we want to
	 * make sure that obtaining the committed_data is done
	 * atomically wrt. completion of any outstanding commits.
	 */
	err = do_get_write_access(handle, jh, 1);
	if (err)
		goto out;

repeat:
	if (!jh->b_committed_data) {
		committed_data = jbd2_alloc(jh2bh(jh)->b_size, GFP_NOFS);
		if (!committed_data) {
			printk(KERN_EMERG "%s: No memory for committed data\n",
				__func__);
			err = -ENOMEM;
			goto out;
		}
	}

	jbd_lock_bh_state(bh);
	if (!jh->b_committed_data) {
		/* Copy out the current buffer contents into the
		 * preserved, committed copy. */
		JBUFFER_TRACE(jh, "generate b_committed data");
		if (!committed_data) {
			jbd_unlock_bh_state(bh);
			goto repeat;
		}

		jh->b_committed_data = committed_data;
		committed_data = NULL;
		memcpy(jh->b_committed_data, bh->b_data, bh->b_size);
	}
	jbd_unlock_bh_state(bh);
out:
	jbd2_journal_put_journal_head(jh);
	if (unlikely(committed_data))
		jbd2_free(committed_data, bh->b_size);
	return err;
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.