linux-kernel - Re: [PATCH bpf-next v3 2/2] bpf: Add tests for bpf_lsm_set_bprm

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Date:   Tue, 17 Nov 2020 23:47:40 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     KP Singh <kpsingh@...omium.org>, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        Pauline Middelink <middelin@...gle.com>
Subject: Re: [PATCH bpf-next v3 2/2] bpf: Add tests for bpf_lsm_set_bprm_opts

On 11/17/20 3:13 AM, KP Singh wrote:
[...]
> +
> +static int run_set_secureexec(int map_fd, int secureexec)
> +{
> +

^ same here

> +	int child_pid, child_status, ret, null_fd;
> +
> +	child_pid = fork();
> +	if (child_pid == 0) {
> +		null_fd = open("/dev/null", O_WRONLY);
> +		if (null_fd == -1)
> +			exit(errno);
> +		dup2(null_fd, STDOUT_FILENO);
> +		dup2(null_fd, STDERR_FILENO);
> +		close(null_fd);
> +
> +		/* Ensure that all executions from hereon are
> +		 * secure by setting a local storage which is read by
> +		 * the bprm_creds_for_exec hook and sets bprm->secureexec.
> +		 */
> +		ret = update_storage(map_fd, secureexec);
> +		if (ret)
> +			exit(ret);
> +
> +		/* If the binary is executed with securexec=1, the dynamic
> +		 * loader ingores and unsets certain variables like LD_PRELOAD,
> +		 * TMPDIR etc. TMPDIR is used here to simplify the example, as
> +		 * LD_PRELOAD requires a real .so file.
> +		 *
> +		 * If the value of TMPDIR is set, the bash command returns 10
> +		 * and if the value is unset, it returns 20.
> +		 */
> +		execle("/bin/bash", "bash", "-c",
> +		       "[[ -z \"${TMPDIR}\" ]] || exit 10 && exit 20", NULL,
> +		       bash_envp);
> +		exit(errno);
> +	} else if (child_pid > 0) {
> +		waitpid(child_pid, &child_status, 0);
> +		ret = WEXITSTATUS(child_status);
> +
> +		/* If a secureexec occured, the exit status should be 20.
> +		 */
> +		if (secureexec && ret == 20)
> +			return 0;
> +
> +		/* If normal execution happened the exit code should be 10.
> +		 */
> +		if (!secureexec && ret == 10)
> +			return 0;
> +

and here (rest looks good to me)

> +	}
> +
> +	return -EINVAL;
> +}
> +