static int update_branch(struct branch *b)
{
	static const char *msg = "fast-import";
	struct ref_transaction *transaction;
	unsigned char old_sha1[20];
	struct strbuf err = STRBUF_INIT;

	if (is_null_sha1(b->sha1)) {
		if (b->delete)
			delete_ref(b->name, NULL, 0);
		return 0;
	}
	if (read_ref(b->name, old_sha1))
		hashclr(old_sha1);
	if (!force_update && !is_null_sha1(old_sha1)) {
		struct commit *old_cmit, *new_cmit;

		old_cmit = lookup_commit_reference_gently(old_sha1, 0);
		new_cmit = lookup_commit_reference_gently(b->sha1, 0);
		if (!old_cmit || !new_cmit)
			return error("Branch %s is missing commits.", b->name);

		if (!in_merge_bases(old_cmit, new_cmit)) {
			warning("Not updating %s"
				" (new tip %s does not contain %s)",
				b->name, sha1_to_hex(b->sha1), sha1_to_hex(old_sha1));
			return -1;
		}
	}
	transaction = ref_transaction_begin(&err);
	if (!transaction ||
	    ref_transaction_update(transaction, b->name, b->sha1, old_sha1,
				   0, msg, &err) ||
	    ref_transaction_commit(transaction, &err)) {
		ref_transaction_free(transaction);
		error("%s", err.buf);
		strbuf_release(&err);
		return -1;
	}
	ref_transaction_free(transaction);
	strbuf_release(&err);
	return 0;
}

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.