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

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Date:   Thu, 14 Jan 2021 19:59:57 +0100
From:   Mickaël Salaün <mic@...ikod.net>
To:     Jann Horn <jannh@...gle.com>
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 14/01/2021 04:21, Jann Horn wrote:
> 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:

OK, I will!

> 
> [...]
>> 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_) {
>  ...
> }

Indeed :)

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