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@linux.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@namei.org Cc: Kees Cook keescook@chromium.org Cc: Serge E. Hallyn serge@hallyn.com

Acked-by: Serge Hallyn serge@hallyn.com

Signed-off-by: Mickaël Salaün mic@linux.microsoft.com Reviewed-by: Jann Horn jannh@google.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@google.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@digikod.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@digikod.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@digikod.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@digikod.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@digikod.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