linux-kernel - Re: [PATCH v26 11/12] samples/landlock: Add a sandbox manager example

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Date:   Thu, 14 Jan 2021 04:21:30 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Mickaël Salaün <mic@...ikod.net>
Cc:     James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...capital.net>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Arnd Bergmann <arnd@...db.de>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Jeff Dike <jdike@...toit.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Richard Weinberger <richard@....at>,
        Shuah Khan <shuah@...nel.org>,
        Vincent Dagonneau <vincent.dagonneau@....gouv.fr>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux API <linux-api@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Mickaël Salaün <mic@...ux.microsoft.com>
Subject: Re: [PATCH v26 11/12] samples/landlock: Add a sandbox manager example

On Wed, Dec 9, 2020 at 8:29 PM Mickaël Salaün <mic@...ikod.net> wrote:
> 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@...gle.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 process
> +         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 by 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 in a read-only way.\n",
> +                               ENV_FS_RO_NAME);
> +               fprintf(stderr, "* %s: list of paths allowed to be used in a read-write way.\n",
> +                               ENV_FS_RO_NAME);

s/ENV_FS_RO_NAME/ENV_FS_RW_NAME/

> +               fprintf(stderr, "\nexample:\n"
> +                               "%s=\"/bin:/lib:/usr:/proc:/etc:/dev/urandom\" "
> +                               "%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
> +                               "%s bash -i\n",
> +                               ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
> +               return 1;
> +       }
> +
> +       ruleset_fd = landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_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_ = errno;
perror("...");
switch (errno_) {
 ...
}

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