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Date: Sun, 16 Apr 2017 23:57:11 +0200
From: Mickaël Salaün <mic@...ikod.net>
To: linux-kernel@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>,
Andy Lutomirski <luto@...capital.net>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Casey Schaufler <casey@...aufler-ca.com>,
Daniel Borkmann <daniel@...earbox.net>,
David Drysdale <drysdale@...gle.com>,
"David S . Miller" <davem@...emloft.net>,
"Eric W . Biederman" <ebiederm@...ssion.com>,
James Morris <james.l.morris@...cle.com>,
Jann Horn <jann@...jh.net>, Jonathan Corbet <corbet@....net>,
Matthew Garrett <mjg59@...f.ucam.org>,
Michael Kerrisk <mtk.manpages@...il.com>,
Kees Cook <keescook@...omium.org>,
Paul Moore <paul@...l-moore.com>,
Sargun Dhillon <sargun@...gun.me>,
"Serge E . Hallyn" <serge@...lyn.com>,
Shuah Khan <shuah@...nel.org>, Tejun Heo <tj@...nel.org>,
Thomas Graf <tgraf@...g.ch>, Will Drewry <wad@...omium.org>,
kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
linux-security-module@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v6 02/11] bpf,landlock: Define an eBPF program
type for Landlock
On 29/03/2017 01:46, Mickaël Salaün wrote:
> Add a new type of eBPF program used by Landlock rules.
>
> This new BPF program type will be registered with the Landlock LSM
> initialization.
>
> Add an initial Landlock Kconfig.
>
> Changes since v5:
> * rename file hooks.c to init.c
> * fix spelling
>
> Changes since v4:
> * merge a minimal (not enabled) LSM code and Kconfig in this commit
>
> Changes since v3:
> * split commit
> * revamp the landlock_context:
> * add arch, syscall_nr and syscall_cmd (ioctl, fcntl…) to be able to
> cross-check action with the event type
> * replace args array with dedicated fields to ease the addition of new
> fields
>
> Signed-off-by: Mickaël Salaün <mic@...ikod.net>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Andy Lutomirski <luto@...capital.net>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: James Morris <james.l.morris@...cle.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Serge E. Hallyn <serge@...lyn.com>
> ---
> include/linux/landlock.h | 23 ++++++++
> include/uapi/linux/bpf.h | 105 +++++++++++++++++++++++++++++++++++
> security/Kconfig | 1 +
> security/Makefile | 2 +
> security/landlock/Kconfig | 18 ++++++
> security/landlock/Makefile | 3 +
> security/landlock/common.h | 25 +++++++++
> security/landlock/init.c | 123 +++++++++++++++++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 105 +++++++++++++++++++++++++++++++++++
> 9 files changed, 405 insertions(+)
> create mode 100644 include/linux/landlock.h
> create mode 100644 security/landlock/Kconfig
> create mode 100644 security/landlock/Makefile
> create mode 100644 security/landlock/common.h
> create mode 100644 security/landlock/init.c
>
[...]
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 0eb71ab9b4fd..619b1f8707cc 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -114,6 +114,7 @@ enum bpf_prog_type {
> BPF_PROG_TYPE_LWT_IN,
> BPF_PROG_TYPE_LWT_OUT,
> BPF_PROG_TYPE_LWT_XMIT,
> + BPF_PROG_TYPE_LANDLOCK,
> };
>
> enum bpf_attach_type {
> @@ -661,4 +662,108 @@ struct xdp_md {
> __u32 data_end;
> };
>
> +/**
> + * enum landlock_subtype_event - event occurring when an action is performed on
> + * a particular kernel object
> + *
> + * An event is a policy decision point which exposes the same context type
> + * (especially the same arg[0-9] field types) for each rule execution.
> + *
> + * @LANDLOCK_SUBTYPE_EVENT_UNSPEC: invalid value
> + * @LANDLOCK_SUBTYPE_EVENT_FS: generic filesystem event
> + */
> +enum landlock_subtype_event {
> + LANDLOCK_SUBTYPE_EVENT_UNSPEC,
> + LANDLOCK_SUBTYPE_EVENT_FS,
> +};
> +#define _LANDLOCK_SUBTYPE_EVENT_LAST LANDLOCK_SUBTYPE_EVENT_FS
[...]
> +/**
> + * DOC: landlock_action_fs
> + *
> + * - %LANDLOCK_ACTION_FS_EXEC: execute a file or walk through a directory
> + * - %LANDLOCK_ACTION_FS_WRITE: modify a file or a directory view (which
> + * include mount actions)
> + * - %LANDLOCK_ACTION_FS_READ: read a file or a directory
> + * - %LANDLOCK_ACTION_FS_NEW: create a file or a directory
> + * - %LANDLOCK_ACTION_FS_GET: open or receive a file
> + * - %LANDLOCK_ACTION_FS_REMOVE: unlink a file or remove a directory
> + *
> + * Each of the following actions are specific to syscall multiplexers. They
> + * fill the syscall_cmd field from &struct landlock_context with their custom
> + * command.
> + *
> + * - %LANDLOCK_ACTION_FS_IOCTL: ioctl command
> + * - %LANDLOCK_ACTION_FS_LOCK: flock or fcntl lock command
> + * - %LANDLOCK_ACTION_FS_FCNTL: fcntl command
> + */
> +#define LANDLOCK_ACTION_FS_EXEC (1ULL << 0)
> +#define LANDLOCK_ACTION_FS_WRITE (1ULL << 1)
> +#define LANDLOCK_ACTION_FS_READ (1ULL << 2)
> +#define LANDLOCK_ACTION_FS_NEW (1ULL << 3)
> +#define LANDLOCK_ACTION_FS_GET (1ULL << 4)
> +#define LANDLOCK_ACTION_FS_REMOVE (1ULL << 5)
> +#define LANDLOCK_ACTION_FS_IOCTL (1ULL << 6)
> +#define LANDLOCK_ACTION_FS_LOCK (1ULL << 7)
> +#define LANDLOCK_ACTION_FS_FCNTL (1ULL << 8)
> +#define _LANDLOCK_ACTION_FS_NB 9
> +#define _LANDLOCK_ACTION_FS_MASK ((1ULL << _LANDLOCK_ACTION_FS_NB) - 1)
> +
> +
> +/**
> + * struct landlock_context - context accessible to a Landlock rule
> + *
> + * @status: bitfield for future use (LANDLOCK_SUBTYPE_STATUS_*)
> + * @arch: indicates system call convention as an AUDIT_ARCH_* value
> + * as defined in <linux/audit.h>
> + * @syscall_nr: the system call number called by the current process (may be
> + * useful to debug: find out from which syscall this request came
> + * from)
> + * @syscall_cmd: contains the command used by a multiplexer syscall (e.g.
> + * ioctl, fcntl, flock)
> + * @event: event type (&enum landlock_subtype_event)
> + * @arg1: event's first optional argument
> + * @arg2: event's second optional argument
> + */
> +struct landlock_context {
> + __u64 status;
> + __u32 arch;
> + __u32 syscall_nr;
> + __u32 syscall_cmd;
> + __u32 event;
> + __u64 arg1;
> + __u64 arg2;
> +};
I plan to simplify and make the FS event more generic for the IOCTL,
LOCK or FCNTL actions. The action flags for the
LANDLOCK_SUBTYPE_EVENT_FS event will remain the same but the syscall_cmd
field will be removed from struct landlock_context. Instead, one of
three dedicated events will be triggered in addition to one of this
three multiplexed actions.
The aim is to trigger the LANDLOCK_SUBTYPE_EVENT_FS for all file system
events (still including IOCTL/LOCK/FCNTL actions). This should avoid a
developer/user to forget such actions. However, when this kind of action
is triggered, a LANDLOCK_SUBTYPE_EVENT_FS_{IOCTL,LOCK,FCNTL} event will
follow. This enable to simplify the struct landlock_context while still
having it as generic as possible. The difference will be that the arg2
field for one of the LANDLOCK_SUBTYPE_EVENT_FS_{IOCTL,LOCK,FCNTL} events
will contain a custom IOCTL, LOCK or FCNTL command (currently in the
syscall_cmd field) instead of a LANDLOCK_ACTION_FS_* value. The same
logic could be used to tighten other actions in the future.
The HOOK_NEW_FS_CMD(...) from [04/11]:security/landlock/hooks_fs.c will
be replaced with dedicated calls.
I also plan to remove the arch and syscall_nr fields. This will make
struct landlock_context even more simple and arch-independent.
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