Re: [PATCH bpf-next v8 08/11] landlock: Add ptrace restrictions

["Mickaël Salaün" <mic@digikod.net>]

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On 27/02/2018 05:17, Andy Lutomirski wrote:
> On Tue, Feb 27, 2018 at 12:41 AM, Mickaël Salaün <mic@digikod.net> wrote:
>> A landlocked process has less privileges than a non-landlocked process
>> and must then be subject to additional restrictions when manipulating
>> processes. To be allowed to use ptrace(2) and related syscalls on a
>> target process, a landlocked process must have a subset of the target
>> process' rules.
>>
>> Signed-off-by: Mickaël Salaün <mic@digikod.net>
>> Cc: Alexei Starovoitov <ast@kernel.org>
>> Cc: Andy Lutomirski <luto@amacapital.net>
>> Cc: Daniel Borkmann <daniel@iogearbox.net>
>> Cc: David S. Miller <davem@davemloft.net>
>> Cc: James Morris <james.l.morris@oracle.com>
>> Cc: Kees Cook <keescook@chromium.org>
>> Cc: Serge E. Hallyn <serge@hallyn.com>
>> ---
>>
>> Changes since v6:
>> * factor out ptrace check
>> * constify pointers
>> * cleanup headers
>> * use the new security_add_hooks()
>> ---
>>  security/landlock/Makefile       |   2 +-
>>  security/landlock/hooks_ptrace.c | 124 +++++++++++++++++++++++++++++++++++++++
>>  security/landlock/hooks_ptrace.h |  11 ++++
>>  security/landlock/init.c         |   2 +
>>  4 files changed, 138 insertions(+), 1 deletion(-)
>>  create mode 100644 security/landlock/hooks_ptrace.c
>>  create mode 100644 security/landlock/hooks_ptrace.h
>>
>> diff --git a/security/landlock/Makefile b/security/landlock/Makefile
>> index d0f532a93b4e..605504d852d3 100644
>> --- a/security/landlock/Makefile
>> +++ b/security/landlock/Makefile
>> @@ -3,4 +3,4 @@ obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
>>  landlock-y := init.o chain.o task.o \
>>         tag.o tag_fs.o \
>>         enforce.o enforce_seccomp.o \
>> -       hooks.o hooks_cred.o hooks_fs.o
>> +       hooks.o hooks_cred.o hooks_fs.o hooks_ptrace.o
>> diff --git a/security/landlock/hooks_ptrace.c b/security/landlock/hooks_ptrace.c
>> new file mode 100644
>> index 000000000000..f1b977b9c808
>> --- /dev/null
>> +++ b/security/landlock/hooks_ptrace.c
>> @@ -0,0 +1,124 @@
>> +/*
>> + * Landlock LSM - ptrace hooks
>> + *
>> + * Copyright © 2017 Mickaël Salaün <mic@digikod.net>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2, as
>> + * published by the Free Software Foundation.
>> + */
>> +
>> +#include <asm/current.h>
>> +#include <linux/errno.h>
>> +#include <linux/kernel.h> /* ARRAY_SIZE */
>> +#include <linux/lsm_hooks.h>
>> +#include <linux/sched.h> /* struct task_struct */
>> +#include <linux/seccomp.h>
>> +
>> +#include "common.h" /* struct landlock_prog_set */
>> +#include "hooks.h" /* landlocked() */
>> +#include "hooks_ptrace.h"
>> +
>> +static bool progs_are_subset(const struct landlock_prog_set *parent,
>> +               const struct landlock_prog_set *child)
>> +{
>> +       size_t i;
>> +
>> +       if (!parent || !child)
>> +               return false;
>> +       if (parent == child)
>> +               return true;
>> +
>> +       for (i = 0; i < ARRAY_SIZE(child->programs); i++) {
> 
> ARRAY_SIZE(child->programs) seems misleading.  Is there no define
> NUM_LANDLOCK_PROG_TYPES or similar?

Yes, there is _LANDLOCK_HOOK_LAST, but this code seems more readable
exactly because it does not require the developer (or the code checking
tools) to know about this static value.


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