linux-kernel - Re: [PATCH bpf-next v3 3/3] bpf: Add a selftest for bpf_ima_inode

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Date:   Thu, 26 Nov 2020 20:29:16 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     KP Singh <kpsingh@...omium.org>
Cc:     James Morris <jmorris@...ei.org>,
        open list <linux-kernel@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, linux-security-module@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        Mimi Zohar <zohar@...ux.ibm.com>
Subject: Re: [PATCH bpf-next v3 3/3] bpf: Add a selftest for bpf_ima_inode_hash

On Tue, Nov 24, 2020 at 7:16 AM KP Singh <kpsingh@...omium.org> wrote:
>
> From: KP Singh <kpsingh@...gle.com>
>
> The test does the following:
>
> - Mounts a loopback filesystem and appends the IMA policy to measure
>   executions only on this file-system. Restricting the IMA policy to a
>   particular filesystem prevents a system-wide IMA policy change.
> - Executes an executable copied to this loopback filesystem.
> - Calls the bpf_ima_inode_hash in the bprm_committed_creds hook and
>   checks if the call succeeded and checks if a hash was calculated.
>
> The test shells out to the added ima_setup.sh script as the setup is
> better handled in a shell script and is more complicated to do in the
> test program or even shelling out individual commands from C.
>
> The list of required configs (i.e. IMA, SECURITYFS,
> IMA_{WRITE,READ}_POLICY) for running this test are also updated.
>
> Signed-off-by: KP Singh <kpsingh@...gle.com>
> ---
>  tools/testing/selftests/bpf/config            |  4 +
>  tools/testing/selftests/bpf/ima_setup.sh      | 80 +++++++++++++++++++
>  .../selftests/bpf/prog_tests/test_ima.c       | 74 +++++++++++++++++
>  tools/testing/selftests/bpf/progs/ima.c       | 28 +++++++
>  4 files changed, 186 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/ima_setup.sh
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/test_ima.c
>  create mode 100644 tools/testing/selftests/bpf/progs/ima.c
>

[...]

> +cleanup() {
> +        local tmp_dir="$1"
> +        local mount_img="${tmp_dir}/test.img"
> +        local mount_dir="${tmp_dir}/mnt"
> +
> +        local loop_devices=$(losetup -j ${mount_img} -O NAME --noheadings)

libbpf and kernel-patches CIs are using BusyBox environment which has
losetup that doesn't support -j option. Is there some way to work
around that? What we have is this:

BusyBox v1.31.1 () multi-call binary.

Usage: losetup [-rP] [-o OFS] {-f|LOOPDEV} FILE: associate loop devices

    losetup -c LOOPDEV: reread file size

    losetup -d LOOPDEV: disassociate

    losetup -a: show status

    losetup -f: show next free loop device

    -o OFS    Start OFS bytes into FILE

    -P    Scan for partitions

    -r    Read-only

    -f    Show/use next free loop device


> +        for loop_dev in "${loop_devices}"; do
> +                losetup -d $loop_dev
> +        done
> +
> +        umount ${mount_dir}
> +        rm -rf ${tmp_dir}
> +}
> +

[...]