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Message-ID: <20210204034628.GC29022@mail.hallyn.com>
Date: Wed, 3 Feb 2021 21:46:28 -0600
From: "Serge E. Hallyn" <serge@...lyn.com>
To: Mickaël Salaün <mic@...ikod.net>
Cc: James Morris <jmorris@...ei.org>, Jann Horn <jannh@...gle.com>,
"Serge E . Hallyn" <serge@...lyn.com>,
Al Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
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@...ts.openwall.com, linux-api@...r.kernel.org,
linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-kselftest@...r.kernel.org,
linux-security-module@...r.kernel.org, x86@...nel.org,
Mickaël Salaün <mic@...ux.microsoft.com>
Subject: Re: [PATCH v28 03/12] landlock: Set up the security framework and
manage credentials
On Tue, Feb 02, 2021 at 05:27:01PM +0100, Mickaël Salaün wrote:
> From: Mickaël Salaün <mic@...ux.microsoft.com>
>
> Process's credentials point to a Landlock domain, which is underneath
> implemented with a ruleset. In the following commits, this domain is
> used to check and enforce the ptrace and filesystem security policies.
> A domain is inherited from a parent to its child the same way a thread
> inherits a seccomp policy.
>
> Cc: James Morris <jmorris@...ei.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Serge E. Hallyn <serge@...lyn.com>
Acked-by: Serge Hallyn <serge@...lyn.com>
> Signed-off-by: Mickaël Salaün <mic@...ux.microsoft.com>
> Reviewed-by: Jann Horn <jannh@...gle.com>
> ---
>
> Changes since v25:
> * Rename function to landlock_add_cred_hooks().
>
> Changes since v23:
> * Add an early check for the current domain in hook_cred_free() to avoid
> superfluous call.
> * Cosmetic cleanup to make the code more readable.
>
> Changes since v22:
> * Add Reviewed-by: Jann Horn <jannh@...gle.com>
>
> Changes since v21:
> * Fix copyright dates.
>
> Changes since v17:
> * Constify returned domain pointers from landlock_get_current_domain()
> and landlock_get_task_domain() helpers.
>
> Changes since v15:
> * Optimize landlocked() for current thread.
> * Display the greeting message when everything is initialized.
>
> Changes since v14:
> * Uses pr_fmt from common.h .
> * Constify variables.
> * Remove useless NULL initialization.
>
> Changes since v13:
> * totally get ride of the seccomp dependency
> * only keep credential management and LSM setup.
>
> Previous changes:
> https://lore.kernel.org/lkml/20191104172146.30797-4-mic@digikod.net/
> ---
> security/Kconfig | 10 +++----
> security/landlock/Makefile | 3 +-
> security/landlock/common.h | 20 +++++++++++++
> security/landlock/cred.c | 46 ++++++++++++++++++++++++++++++
> security/landlock/cred.h | 58 ++++++++++++++++++++++++++++++++++++++
> security/landlock/setup.c | 31 ++++++++++++++++++++
> security/landlock/setup.h | 16 +++++++++++
> 7 files changed, 178 insertions(+), 6 deletions(-)
> create mode 100644 security/landlock/common.h
> create mode 100644 security/landlock/cred.c
> create mode 100644 security/landlock/cred.h
> create mode 100644 security/landlock/setup.c
> create mode 100644 security/landlock/setup.h
>
> diff --git a/security/Kconfig b/security/Kconfig
> index 15a4342b5d01..0ced7fd33e4d 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -278,11 +278,11 @@ endchoice
>
> config LSM
> string "Ordered list of enabled LSMs"
> - default "lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor,bpf" if DEFAULT_SECURITY_SMACK
> - default "lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo,bpf" if DEFAULT_SECURITY_APPARMOR
> - default "lockdown,yama,loadpin,safesetid,integrity,tomoyo,bpf" if DEFAULT_SECURITY_TOMOYO
> - default "lockdown,yama,loadpin,safesetid,integrity,bpf" if DEFAULT_SECURITY_DAC
> - default "lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor,bpf"
> + default "landlock,lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor,bpf" if DEFAULT_SECURITY_SMACK
> + default "landlock,lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo,bpf" if DEFAULT_SECURITY_APPARMOR
> + default "landlock,lockdown,yama,loadpin,safesetid,integrity,tomoyo,bpf" if DEFAULT_SECURITY_TOMOYO
> + default "landlock,lockdown,yama,loadpin,safesetid,integrity,bpf" if DEFAULT_SECURITY_DAC
> + default "landlock,lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor,bpf"
> help
> A comma-separated list of LSMs, in initialization order.
> Any LSMs left off this list will be ignored. This can be
> diff --git a/security/landlock/Makefile b/security/landlock/Makefile
> index d846eba445bb..041ea242e627 100644
> --- a/security/landlock/Makefile
> +++ b/security/landlock/Makefile
> @@ -1,3 +1,4 @@
> obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
>
> -landlock-y := object.o ruleset.o
> +landlock-y := setup.o object.o ruleset.o \
> + cred.o
> diff --git a/security/landlock/common.h b/security/landlock/common.h
> new file mode 100644
> index 000000000000..5dc0fe15707d
> --- /dev/null
> +++ b/security/landlock/common.h
> @@ -0,0 +1,20 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Landlock LSM - Common constants and helpers
> + *
> + * Copyright © 2016-2020 Mickaël Salaün <mic@...ikod.net>
> + * Copyright © 2018-2020 ANSSI
> + */
> +
> +#ifndef _SECURITY_LANDLOCK_COMMON_H
> +#define _SECURITY_LANDLOCK_COMMON_H
> +
> +#define LANDLOCK_NAME "landlock"
> +
> +#ifdef pr_fmt
> +#undef pr_fmt
> +#endif
> +
> +#define pr_fmt(fmt) LANDLOCK_NAME ": " fmt
> +
> +#endif /* _SECURITY_LANDLOCK_COMMON_H */
> diff --git a/security/landlock/cred.c b/security/landlock/cred.c
> new file mode 100644
> index 000000000000..6725af24c684
> --- /dev/null
> +++ b/security/landlock/cred.c
> @@ -0,0 +1,46 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Landlock LSM - Credential hooks
> + *
> + * Copyright © 2017-2020 Mickaël Salaün <mic@...ikod.net>
> + * Copyright © 2018-2020 ANSSI
> + */
> +
> +#include <linux/cred.h>
> +#include <linux/lsm_hooks.h>
> +
> +#include "common.h"
> +#include "cred.h"
> +#include "ruleset.h"
> +#include "setup.h"
> +
> +static int hook_cred_prepare(struct cred *const new,
> + const struct cred *const old, const gfp_t gfp)
> +{
> + struct landlock_ruleset *const old_dom = landlock_cred(old)->domain;
> +
> + if (old_dom) {
> + landlock_get_ruleset(old_dom);
> + landlock_cred(new)->domain = old_dom;
> + }
> + return 0;
> +}
> +
> +static void hook_cred_free(struct cred *const cred)
> +{
> + struct landlock_ruleset *const dom = landlock_cred(cred)->domain;
> +
> + if (dom)
> + landlock_put_ruleset_deferred(dom);
> +}
> +
> +static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
> + LSM_HOOK_INIT(cred_prepare, hook_cred_prepare),
> + LSM_HOOK_INIT(cred_free, hook_cred_free),
> +};
> +
> +__init void landlock_add_cred_hooks(void)
> +{
> + security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
> + LANDLOCK_NAME);
> +}
> diff --git a/security/landlock/cred.h b/security/landlock/cred.h
> new file mode 100644
> index 000000000000..5f99d3decade
> --- /dev/null
> +++ b/security/landlock/cred.h
> @@ -0,0 +1,58 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Landlock LSM - Credential hooks
> + *
> + * Copyright © 2019-2020 Mickaël Salaün <mic@...ikod.net>
> + * Copyright © 2019-2020 ANSSI
> + */
> +
> +#ifndef _SECURITY_LANDLOCK_CRED_H
> +#define _SECURITY_LANDLOCK_CRED_H
> +
> +#include <linux/cred.h>
> +#include <linux/init.h>
> +#include <linux/rcupdate.h>
> +
> +#include "ruleset.h"
> +#include "setup.h"
> +
> +struct landlock_cred_security {
> + struct landlock_ruleset *domain;
> +};
> +
> +static inline struct landlock_cred_security *landlock_cred(
> + const struct cred *cred)
> +{
> + return cred->security + landlock_blob_sizes.lbs_cred;
> +}
> +
> +static inline const struct landlock_ruleset *landlock_get_current_domain(void)
> +{
> + return landlock_cred(current_cred())->domain;
> +}
> +
> +/*
> + * The call needs to come from an RCU read-side critical section.
> + */
> +static inline const struct landlock_ruleset *landlock_get_task_domain(
> + const struct task_struct *const task)
> +{
> + return landlock_cred(__task_cred(task))->domain;
> +}
> +
> +static inline bool landlocked(const struct task_struct *const task)
> +{
> + bool has_dom;
> +
> + if (task == current)
> + return !!landlock_get_current_domain();
> +
> + rcu_read_lock();
> + has_dom = !!landlock_get_task_domain(task);
> + rcu_read_unlock();
> + return has_dom;
> +}
> +
> +__init void landlock_add_cred_hooks(void);
> +
> +#endif /* _SECURITY_LANDLOCK_CRED_H */
> diff --git a/security/landlock/setup.c b/security/landlock/setup.c
> new file mode 100644
> index 000000000000..8661112fb238
> --- /dev/null
> +++ b/security/landlock/setup.c
> @@ -0,0 +1,31 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Landlock LSM - Security framework setup
> + *
> + * Copyright © 2016-2020 Mickaël Salaün <mic@...ikod.net>
> + * Copyright © 2018-2020 ANSSI
> + */
> +
> +#include <linux/init.h>
> +#include <linux/lsm_hooks.h>
> +
> +#include "common.h"
> +#include "cred.h"
> +#include "setup.h"
> +
> +struct lsm_blob_sizes landlock_blob_sizes __lsm_ro_after_init = {
> + .lbs_cred = sizeof(struct landlock_cred_security),
> +};
> +
> +static int __init landlock_init(void)
> +{
> + landlock_add_cred_hooks();
> + pr_info("Up and running.\n");
> + return 0;
> +}
> +
> +DEFINE_LSM(LANDLOCK_NAME) = {
> + .name = LANDLOCK_NAME,
> + .init = landlock_init,
> + .blobs = &landlock_blob_sizes,
> +};
> diff --git a/security/landlock/setup.h b/security/landlock/setup.h
> new file mode 100644
> index 000000000000..9fdbf33fcc33
> --- /dev/null
> +++ b/security/landlock/setup.h
> @@ -0,0 +1,16 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Landlock LSM - Security framework setup
> + *
> + * Copyright © 2016-2020 Mickaël Salaün <mic@...ikod.net>
> + * Copyright © 2018-2020 ANSSI
> + */
> +
> +#ifndef _SECURITY_LANDLOCK_SETUP_H
> +#define _SECURITY_LANDLOCK_SETUP_H
> +
> +#include <linux/lsm_hooks.h>
> +
> +extern struct lsm_blob_sizes landlock_blob_sizes;
> +
> +#endif /* _SECURITY_LANDLOCK_SETUP_H */
> --
> 2.30.0
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