[PATCH v26 11/12] samples/landlock: Add a sandbox manager example

[Mickaël Salaün]

On 14/01/2021 04:21, Jann Horn wrote:
> On Wed, Dec 9, 2020 at 8:29 PM Mickaël Salaün <mic at digikod.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 at google.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.)
>