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From: Kees Cook <keescook@chromium.org>
To: "Mickaël Salaün" <mic@digikod.net>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Arnd Bergmann <arnd@arndb.de>,
	Casey Schaufler <casey@schaufler-ca.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Daniel Mack <daniel@zonque.org>,
	David Drysdale <drysdale@google.com>,
	"David S . Miller" <davem@davemloft.net>,
	Elena Reshetova <elena.reshetova@intel.com>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	James Morris <james.l.morris@oracle.com>,
	Paul Moore <pmoore@redhat.com>, Sargun Dhillon <sargun@sargun.me>,
	"Serge E . Hallyn" <serge@hallyn.com>, Tejun Heo <tj@kernel.org>,
	Will Drewry <wad@chromium.org>,
	"kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
	Linux API <linux-api@vger.kernel.org>,
	linux-security-module <linux-security-module@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	Cgroups <cgroups@vger.kernel.org>
Subject: Re: [RFC v3 07/22] landlock: Handle file comparisons
Date: Mon, 3 Oct 2016 16:30:21 -0700
Message-ID: <CAGXu5jLnVyeAMPWwP=ovZuE+vmmqxSd4WyZ6O1inA1ie107k8Q@mail.gmail.com> (raw)
In-Reply-To: <20160914072415.26021-8-mic@digikod.net>

On Wed, Sep 14, 2016 at 12:24 AM, Mickaël Salaün <mic@digikod.net> wrote:
> Add eBPF functions to compare file system access with a Landlock file
> system handle:
> * bpf_landlock_cmp_fs_prop_with_struct_file(prop, map, map_op, file)
>   This function allows to compare the dentry, inode, device or mount
>   point of the currently accessed file, with a reference handle.
> * bpf_landlock_cmp_fs_beneath_with_struct_file(opt, map, map_op, file)
>   This function allows an eBPF program to check if the current accessed
>   file is the same or in the hierarchy of a reference handle.
>
> The goal of file system handle is to abstract kernel objects such as a
> struct file or a struct inode. Userland can create this kind of handle
> thanks to the BPF_MAP_UPDATE_ELEM command. The element is a struct
> landlock_handle containing the handle type (e.g.
> BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD) and a file descriptor. This could
> also be any descriptions able to match a struct file or a struct inode
> (e.g. path or glob string).
>
> Changes since v2:
> * add MNT_INTERNAL check to only add file handle from user-visible FS
>   (e.g. no anonymous inode)
> * replace struct file* with struct path* in map_landlock_handle
> * add BPF protos
> * fix bpf_landlock_cmp_fs_prop_with_struct_file()
>
> 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>
> Link: https://lkml.kernel.org/r/CALCETrWwTiz3kZTkEgOW24-DvhQq6LftwEXh77FD2G5o71yD7g@mail.gmail.com
> ---
>  include/linux/bpf.h            |  10 +++
>  include/uapi/linux/bpf.h       |  49 +++++++++++
>  kernel/bpf/arraymap.c          |  21 +++++
>  kernel/bpf/verifier.c          |   8 ++
>  security/landlock/Makefile     |   2 +-
>  security/landlock/checker_fs.c | 179 +++++++++++++++++++++++++++++++++++++++++
>  security/landlock/checker_fs.h |  20 +++++
>  security/landlock/lsm.c        |   6 ++
>  8 files changed, 294 insertions(+), 1 deletion(-)
>  create mode 100644 security/landlock/checker_fs.c
>  create mode 100644 security/landlock/checker_fs.h
> [...]
> diff --git a/security/landlock/checker_fs.c b/security/landlock/checker_fs.c
> new file mode 100644
> index 000000000000..39eb85dc7d18
> --- /dev/null
> +++ b/security/landlock/checker_fs.c
> @@ -0,0 +1,179 @@
> +/*
> + * Landlock LSM - File System Checkers
> + *
> + * Copyright (C) 2016  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 <linux/bpf.h> /* enum bpf_map_array_op */
> +#include <linux/errno.h>
> +#include <linux/fs.h> /* path_is_under() */
> +#include <linux/path.h> /* struct path */
> +
> +#include "checker_fs.h"
> +
> +#define EQUAL_NOT_NULL(a, b) (a && a == b)
> +
> +/*
> + * bpf_landlock_cmp_fs_prop_with_struct_file
> + *
> + * Cf. include/uapi/linux/bpf.h
> + */
> +static inline u64 bpf_landlock_cmp_fs_prop_with_struct_file(u64 r1_property,
> +               u64 r2_map, u64 r3_map_op, u64 r4_file, u64 r5)
> +{
> +       u8 property = (u8) r1_property;
> +       struct bpf_map *map = (struct bpf_map *) (unsigned long) r2_map;
> +       enum bpf_map_array_op map_op = r3_map_op;
> +       struct file *file = (struct file *) (unsigned long) r4_file;
> +       struct bpf_array *array = container_of(map, struct bpf_array, map);
> +       struct path *p1, *p2;
> +       struct map_landlock_handle *handle;
> +       int i;
> +
> +       /* ARG_CONST_PTR_TO_LANDLOCK_HANDLE_FS is an arraymap */
> +       if (unlikely(!map)) {
> +               WARN_ON(1);
> +               return -EFAULT;
> +       }

Just some minor style/readability nits...

This is more readable as:

if (WARN_ON(!map))
    return -EFAULT;

(WARN_ON already includes the unlikely() and passes through the test result.)

> +       if (unlikely(!file))
> +               return -ENOENT;
> +       if (unlikely((property | _LANDLOCK_FLAG_FS_MASK) != _LANDLOCK_FLAG_FS_MASK))
> +               return -EINVAL;
> +
> +       /* for now, only handle OP_OR */
> +       switch (map_op) {
> +       case BPF_MAP_ARRAY_OP_OR:
> +               break;
> +       case BPF_MAP_ARRAY_OP_UNSPEC:
> +       case BPF_MAP_ARRAY_OP_AND:
> +       case BPF_MAP_ARRAY_OP_XOR:
> +       default:
> +               return -EINVAL;
> +       }
> +       p2 = &file->f_path;
> +
> +       synchronize_rcu();
> +
> +       for (i = 0; i < array->n_entries; i++) {
> +               bool result_dentry = !(property & LANDLOCK_FLAG_FS_DENTRY);
> +               bool result_inode = !(property & LANDLOCK_FLAG_FS_INODE);
> +               bool result_device = !(property & LANDLOCK_FLAG_FS_DEVICE);
> +               bool result_mount = !(property & LANDLOCK_FLAG_FS_MOUNT);
> +
> +               handle = (struct map_landlock_handle *)
> +                               (array->value + array->elem_size * i);
> +
> +               if (handle->type != BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD) {
> +                       WARN_ON(1);
> +                       return -EFAULT;
> +               }

Same here... and in the other function (much of which seems to repeat
-- can some of these checks be put into common functions?)

-Kees

-- 
Kees Cook
Nexus Security

  parent reply index

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-14  7:23 [RFC v3 00/22] Landlock LSM: Unprivileged sandboxing Mickaël Salaün
2016-09-14  7:23 ` [RFC v3 01/22] landlock: Add Kconfig Mickaël Salaün
2016-09-14  7:23 ` [RFC v3 02/22] bpf: Move u64_to_ptr() to BPF headers and inline it Mickaël Salaün
2016-09-14  7:23 ` [RFC v3 03/22] bpf,landlock: Add a new arraymap type to deal with (Landlock) handles Mickaël Salaün
2016-09-14 18:51   ` Alexei Starovoitov
2016-09-14 23:22     ` Mickaël Salaün
2016-09-14 23:28       ` Alexei Starovoitov
2016-09-15 21:51         ` Mickaël Salaün
2016-10-03 23:53   ` Kees Cook
2016-10-05 22:02     ` Mickaël Salaün
2016-09-14  7:23 ` [RFC v3 04/22] bpf: Set register type according to is_valid_access() Mickaël Salaün
2016-10-19 14:54   ` Thomas Graf
2016-10-19 15:10     ` Daniel Borkmann
2016-09-14  7:23 ` [RFC v3 05/22] bpf,landlock: Add eBPF program subtype and is_valid_subtype() verifier Mickaël Salaün
2016-10-19 15:01   ` Thomas Graf
2016-09-14  7:23 ` [RFC v3 06/22] landlock: Add LSM hooks Mickaël Salaün
2016-10-19 15:19   ` Thomas Graf
2016-10-19 22:42     ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 07/22] landlock: Handle file comparisons Mickaël Salaün
2016-09-14 19:07   ` Jann Horn
2016-09-14 22:39     ` Mickaël Salaün
2016-09-14 21:06   ` Alexei Starovoitov
2016-09-14 23:02     ` Mickaël Salaün
2016-09-14 23:24       ` Alexei Starovoitov
2016-09-15 21:25         ` Mickaël Salaün
2016-09-20  0:12           ` lsm naming dilemma. " Alexei Starovoitov
2016-09-20  1:10             ` Sargun Dhillon
2016-09-20 16:58               ` Mickaël Salaün
2016-10-03 23:30   ` Kees Cook [this message]
2016-09-14  7:24 ` [RFC v3 08/22] seccomp: Fix documentation for struct seccomp_filter Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 09/22] seccomp: Move struct seccomp_filter in seccomp.h Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 10/22] seccomp: Split put_seccomp_filter() with put_seccomp() Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 11/22] seccomp,landlock: Handle Landlock hooks per process hierarchy Mickaël Salaün
2016-09-14 18:43   ` Andy Lutomirski
2016-09-14 22:34     ` Mickaël Salaün
2016-10-03 23:52       ` Kees Cook
2016-10-05 21:05         ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 12/22] bpf: Cosmetic change for bpf_prog_attach() Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 13/22] bpf/cgroup: Replace struct bpf_prog with union bpf_object Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 14/22] bpf/cgroup: Make cgroup_bpf_update() return an error code Mickaël Salaün
2016-09-14 21:16   ` Alexei Starovoitov
2016-09-14  7:24 ` [RFC v3 15/22] bpf/cgroup: Move capability check Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 16/22] bpf/cgroup,landlock: Handle Landlock hooks per cgroup Mickaël Salaün
2016-10-03 23:43   ` Kees Cook
2016-10-05 20:58     ` Mickaël Salaün
2016-10-05 21:25       ` Kees Cook
2016-09-14  7:24 ` [RFC v3 17/22] cgroup: Add access check for cgroup_get_from_fd() Mickaël Salaün
2016-09-14 22:06   ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 18/22] cgroup,landlock: Add CGRP_NO_NEW_PRIVS to handle unprivileged hooks Mickaël Salaün
2016-09-14 18:27   ` Andy Lutomirski
2016-09-14 22:11     ` Mickaël Salaün
2016-09-15  1:25       ` Andy Lutomirski
2016-09-15  2:19         ` Alexei Starovoitov
2016-09-15  2:27           ` Andy Lutomirski
2016-09-15  4:00             ` Alexei Starovoitov
2016-09-15  4:08               ` Andy Lutomirski
2016-09-15  4:31                 ` Alexei Starovoitov
2016-09-15  4:38                   ` Andy Lutomirski
2016-09-15  4:48                     ` Alexei Starovoitov
2016-09-15 19:41                       ` Mickaël Salaün
2016-09-20  4:37                         ` Sargun Dhillon
2016-09-20 17:02                           ` Mickaël Salaün
2016-09-15 19:35         ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 19/22] landlock: Add interrupted origin Mickaël Salaün
2016-09-14 18:29   ` Andy Lutomirski
2016-09-14 22:14     ` Mickaël Salaün
2016-09-15  1:19       ` Andy Lutomirski
2016-10-03 23:46         ` Kees Cook
2016-10-05 21:01           ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 20/22] landlock: Add update and debug access flags Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 21/22] bpf,landlock: Add optional skb pointer in the Landlock context Mickaël Salaün
2016-09-14 21:20   ` Alexei Starovoitov
2016-09-14 22:46     ` Mickaël Salaün
2016-09-14  7:24 ` [RFC v3 22/22] samples/landlock: Add sandbox example Mickaël Salaün
2016-09-14 21:24   ` Alexei Starovoitov
2016-09-14 14:36 ` [RFC v3 00/22] Landlock LSM: Unprivileged sandboxing David Laight

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