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From:   Jann Horn <jannh@google.com>
Date:   Thu, 14 Jan 2021 04:21:30 +0100
Message-ID: <CAG48ez2yQNvcCrmCCBZKy_cxoZzNgremxWMia1YHsgaj4edqrA@mail.gmail.com>
Subject: Re: [PATCH v26 11/12] samples/landlock: Add a sandbox manager example
To:     =?UTF-8?B?TWlja2HDq2wgU2FsYcO8bg==?= <mic@digikod.net>
Cc:     James Morris <jmorris@namei.org>,
        "Serge E . Hallyn" <serge@hallyn.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Andy Lutomirski <luto@amacapital.net>,
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        Jeff Dike <jdike@addtoit.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Kees Cook <keescook@chromium.org>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Richard Weinberger <richard@nod.at>,
        Shuah Khan <shuah@kernel.org>,
        Vincent Dagonneau <vincent.dagonneau@ssi.gouv.fr>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
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        =?UTF-8?B?TWlja2HDq2wgU2FsYcO8bg==?= <mic@linux.microsoft.com>
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On Wed, Dec 9, 2020 at 8:29 PM Micka=C3=ABl Sala=C3=BCn <mic@digikod.net> w=
rote:
> Add a basic sandbox tool to launch a command which can only access a
> whitelist of file hierarchies in a read-only or read-write way.

I have to admit that I didn't really look at this closely before
because it's just sample code... but I guess I should. You can add

Reviewed-by: Jann Horn <jannh@google.com>

if you fix the following nits:

[...]
> diff --git a/samples/Kconfig b/samples/Kconfig
[...]
> +config SAMPLE_LANDLOCK
> +       bool "Build Landlock sample code"
> +       depends on HEADERS_INSTALL
> +       help
> +         Build a simple Landlock sandbox manager able to launch a proces=
s
> +         restricted by a user-defined filesystem access control.

nit: s/filesystem access control/filesystem access control policy/

[...]
> diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
[...]
> +/*
> + * Simple Landlock sandbox manager able to launch a process restricted b=
y a
> + * user-defined filesystem access control.

nit: s/filesystem access control/filesystem access control policy/

[...]
> +int main(const int argc, char *const argv[], char *const *const envp)
> +{
[...]
> +       if (argc < 2) {
[...]
> +               fprintf(stderr, "* %s: list of paths allowed to be used i=
n a read-only way.\n",
> +                               ENV_FS_RO_NAME);
> +               fprintf(stderr, "* %s: list of paths allowed to be used i=
n a read-write way.\n",
> +                               ENV_FS_RO_NAME);

s/ENV_FS_RO_NAME/ENV_FS_RW_NAME/

> +               fprintf(stderr, "\nexample:\n"
> +                               "%s=3D\"/bin:/lib:/usr:/proc:/etc:/dev/ur=
andom\" "
> +                               "%s=3D\"/dev/null:/dev/full:/dev/zero:/de=
v/pts:/tmp\" "
> +                               "%s bash -i\n",
> +                               ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
> +               return 1;
> +       }
> +
> +       ruleset_fd =3D landlock_create_ruleset(&ruleset_attr, sizeof(rule=
set_attr), 0);
> +       if (ruleset_fd < 0) {
> +               perror("Failed to create a ruleset");
> +               switch (errno) {

(Just as a note: In theory perror() can change the value of errno, as
far as I know - so AFAIK you'd theoretically have to do something
like:

int errno_ =3D errno;
perror("...");
switch (errno_) {
 ...
}

I'll almost certainly work fine as-is in practice though.)