From patchwork Tue Oct 29 17:15:00 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= X-Patchwork-Id: 11218361 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 73EF913BD for ; Tue, 29 Oct 2019 17:40:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4638320856 for ; Tue, 29 Oct 2019 17:40:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728827AbfJ2RkY (ORCPT ); Tue, 29 Oct 2019 13:40:24 -0400 Received: from smtp-sh.infomaniak.ch ([128.65.195.4]:55764 "EHLO smtp-sh.infomaniak.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725905AbfJ2RkY (ORCPT ); Tue, 29 Oct 2019 13:40:24 -0400 Received: from smtp8.infomaniak.ch (smtp8.infomaniak.ch [83.166.132.38]) by smtp-sh.infomaniak.ch (8.14.5/8.14.5) with ESMTP id x9THFO07006023 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 29 Oct 2019 18:15:24 +0100 Received: from localhost (ns3096276.ip-94-23-54.eu [94.23.54.103]) (authenticated bits=0) by smtp8.infomaniak.ch (8.14.5/8.14.5) with ESMTP id x9THFNGc168214; Tue, 29 Oct 2019 18:15:23 +0100 From: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= To: linux-kernel@vger.kernel.org Cc: =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Alexei Starovoitov , Andy Lutomirski , Casey Schaufler , Daniel Borkmann , David Drysdale , Florent Revest , James Morris , Jann Horn , John Johansen , Jonathan Corbet , Kees Cook , KP Singh , Michael Kerrisk , =?utf-8?q?Micka=C3=ABl_Sala=C3=BCn?= , Paul Moore , Sargun Dhillon , "Serge E . Hallyn" , Shuah Khan , Stephen Smalley , Tejun Heo , Tetsuo Handa , Tycho Andersen , Will Drewry , bpf@vger.kernel.org, kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-security-module@vger.kernel.org Subject: [PATCH bpf-next v11 2/7] landlock: Add the management of domains Date: Tue, 29 Oct 2019 18:15:00 +0100 Message-Id: <20191029171505.6650-3-mic@digikod.net> X-Mailer: git-send-email 2.24.0.rc1 In-Reply-To: <20191029171505.6650-1-mic@digikod.net> References: <20191029171505.6650-1-mic@digikod.net> MIME-Version: 1.0 X-Antivirus: Dr.Web (R) for Unix mail servers drweb plugin ver.6.0.2.8 X-Antivirus-Code: 0x100000 Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: A Landlock domain is a set of eBPF programs. There is a list for each different program types that can be run on a specific Landlock hook (e.g. ptrace). A domain is tied to a set of subjects (i.e. tasks). A Landlock program should not try (nor be able) to infer which subject is currently enforced, but to have a unique security policy for all subjects tied to the same domain. This make the reasoning much easier and help avoid pitfalls. The next commits tie a domain to a task's credentials thanks to seccomp(2), but we could use cgroups or a security file-system to enforce a sysadmin-defined policy . Signed-off-by: Mickaël Salaün Cc: Alexei Starovoitov Cc: Andy Lutomirski Cc: Daniel Borkmann Cc: James Morris Cc: Kees Cook Cc: Serge E. Hallyn Cc: Will Drewry --- Changes since v10: * rename files and names to clearly define a domain * create a standalone patch to ease review --- security/landlock/Makefile | 3 +- security/landlock/common.h | 38 +++++ security/landlock/domain_manage.c | 265 ++++++++++++++++++++++++++++++ security/landlock/domain_manage.h | 23 +++ 4 files changed, 328 insertions(+), 1 deletion(-) create mode 100644 security/landlock/domain_manage.c create mode 100644 security/landlock/domain_manage.h diff --git a/security/landlock/Makefile b/security/landlock/Makefile index 682b798c6b76..dd5f70185778 100644 --- a/security/landlock/Makefile +++ b/security/landlock/Makefile @@ -1,4 +1,5 @@ obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o landlock-y := \ - bpf_verify.o bpf_ptrace.o + bpf_verify.o bpf_ptrace.o \ + domain_manage.o diff --git a/security/landlock/common.h b/security/landlock/common.h index 0234c4bc4acd..fb2990eb5fb4 100644 --- a/security/landlock/common.h +++ b/security/landlock/common.h @@ -11,11 +11,49 @@ #include #include +#include enum landlock_hook_type { LANDLOCK_HOOK_PTRACE = 1, }; +#define _LANDLOCK_HOOK_LAST LANDLOCK_HOOK_PTRACE + +struct landlock_prog_list { + struct landlock_prog_list *prev; + struct bpf_prog *prog; + refcount_t usage; +}; + +/** + * struct landlock_domain - Landlock programs enforced on a set of tasks + * + * When prepending a new program, if &struct landlock_domain is shared with + * other tasks, then duplicate it and prepend the program to this new &struct + * landlock_domain. + * + * @usage: reference count to manage the object lifetime. When a task needs to + * add Landlock programs and if @usage is greater than 1, then the + * task must duplicate &struct landlock_domain to not change the + * children's programs as well. + * @programs: array of non-NULL &struct landlock_prog_list pointers + */ +struct landlock_domain { + struct landlock_prog_list *programs[_LANDLOCK_HOOK_LAST]; + refcount_t usage; +}; + +/** + * get_hook_index - get an index for the programs of struct landlock_prog_set + * + * @type: a Landlock hook type + */ +static inline size_t get_hook_index(enum landlock_hook_type type) +{ + /* type ID > 0 for loaded programs */ + return type - 1; +} + static inline enum landlock_hook_type get_hook_type(const struct bpf_prog *prog) { switch (prog->expected_attach_type) { diff --git a/security/landlock/domain_manage.c b/security/landlock/domain_manage.c new file mode 100644 index 000000000000..c955b9c95c84 --- /dev/null +++ b/security/landlock/domain_manage.c @@ -0,0 +1,265 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - domain management + * + * Copyright © 2016-2019 Mickaël Salaün + * Copyright © 2018-2019 ANSSI + */ + +#include +#include +#include +#include +#include + +#include "common.h" +#include "domain_manage.h" + +void landlock_get_domain(struct landlock_domain *dom) +{ + if (!dom) + return; + refcount_inc(&dom->usage); +} + +static void put_landlock_prog_list(struct landlock_prog_list *prog_list) +{ + struct landlock_prog_list *orig = prog_list; + + /* clean up single-reference branches iteratively */ + while (orig && refcount_dec_and_test(&orig->usage)) { + struct landlock_prog_list *freeme = orig; + + if (orig->prog) + bpf_prog_put(orig->prog); + orig = orig->prev; + kfree(freeme); + } +} + +void landlock_put_domain(struct landlock_domain *domain) +{ + if (domain && refcount_dec_and_test(&domain->usage)) { + size_t i; + + for (i = 0; i < ARRAY_SIZE(domain->programs); i++) + put_landlock_prog_list(domain->programs[i]); + kfree(domain); + } +} + +static struct landlock_domain *new_landlock_domain(void) +{ + struct landlock_domain *domain; + + /* array filled with NULL values */ + domain = kzalloc(sizeof(*domain), GFP_KERNEL); + if (!domain) + return ERR_PTR(-ENOMEM); + refcount_set(&domain->usage, 1); + return domain; +} + +/** + * store_landlock_prog - prepend and deduplicate a Landlock prog_list + * + * Prepend @prog to @init_domain while ignoring @prog if they are already in + * @ref_domain. Whatever is the result of this function call, you can call + * bpf_prog_put(@prog) after. + * + * @init_domain: empty domain to prepend to + * @ref_domain: domain to check for duplicate programs + * @prog: program to prepend + * + * Return -errno on error or 0 if @prog was successfully stored. + */ +static int store_landlock_prog(struct landlock_domain *init_domain, + const struct landlock_domain *ref_domain, + struct bpf_prog *prog) +{ + struct landlock_prog_list *tmp_list = NULL; + int err; + size_t hook; + enum landlock_hook_type last_type; + struct bpf_prog *new = prog; + + /* allocate all the memory we need */ + struct landlock_prog_list *new_list; + + last_type = get_hook_type(new); + + /* ignore duplicate programs */ + if (ref_domain) { + struct landlock_prog_list *ref; + + hook = get_hook_index(get_hook_type(new)); + for (ref = ref_domain->programs[hook]; ref; + ref = ref->prev) { + if (ref->prog == new) + return -EINVAL; + } + } + + new = bpf_prog_inc(new); + if (IS_ERR(new)) { + err = PTR_ERR(new); + goto put_tmp_list; + } + new_list = kzalloc(sizeof(*new_list), GFP_KERNEL); + if (!new_list) { + bpf_prog_put(new); + err = -ENOMEM; + goto put_tmp_list; + } + /* ignore Landlock types in this tmp_list */ + new_list->prog = new; + new_list->prev = tmp_list; + refcount_set(&new_list->usage, 1); + tmp_list = new_list; + + if (!tmp_list) + /* inform user space that this program was already added */ + return -EEXIST; + + /* properly store the list (without error cases) */ + while (tmp_list) { + struct landlock_prog_list *new_list; + + new_list = tmp_list; + tmp_list = tmp_list->prev; + /* do not increment the previous prog list usage */ + hook = get_hook_index(get_hook_type(new_list->prog)); + new_list->prev = init_domain->programs[hook]; + /* no need to add from the last program to the first because + * each of them are a different Landlock type */ + smp_store_release(&init_domain->programs[hook], new_list); + } + return 0; + +put_tmp_list: + put_landlock_prog_list(tmp_list); + return err; +} + +/* limit Landlock programs set to 256KB */ +#define LANDLOCK_PROGRAMS_MAX_PAGES (1 << 6) + +/** + * landlock_prepend_prog - attach a Landlock prog_list to @current_domain + * + * Whatever is the result of this function call, you can call + * bpf_prog_put(@prog) after. + * + * @current_domain: landlock_domain pointer, must be (RCU-)locked (if needed) + * to prevent a concurrent put/free. This pointer must not be + * freed after the call. + * @prog: non-NULL Landlock prog_list to prepend to @current_domain. @prog will + * be owned by landlock_prepend_prog() and freed if an error happened. + * + * Return @current_domain or a new pointer when OK. Return a pointer error + * otherwise. + */ +struct landlock_domain *landlock_prepend_prog( + struct landlock_domain *current_domain, + struct bpf_prog *prog) +{ + struct landlock_domain *new_domain = current_domain; + unsigned long pages; + int err; + size_t i; + struct landlock_domain tmp_domain = {}; + + if (prog->type != BPF_PROG_TYPE_LANDLOCK_HOOK) + return ERR_PTR(-EINVAL); + + /* validate memory size allocation */ + pages = prog->pages; + if (current_domain) { + size_t i; + + for (i = 0; i < ARRAY_SIZE(current_domain->programs); i++) { + struct landlock_prog_list *walker_p; + + for (walker_p = current_domain->programs[i]; + walker_p; walker_p = walker_p->prev) + pages += walker_p->prog->pages; + } + /* count a struct landlock_domain if we need to allocate one */ + if (refcount_read(¤t_domain->usage) != 1) + pages += round_up(sizeof(*current_domain), PAGE_SIZE) + / PAGE_SIZE; + } + if (pages > LANDLOCK_PROGRAMS_MAX_PAGES) + return ERR_PTR(-E2BIG); + + /* ensure early that we can allocate enough memory for the new + * prog_lists */ + err = store_landlock_prog(&tmp_domain, current_domain, prog); + if (err) + return ERR_PTR(err); + + /* + * Each task_struct points to an array of prog list pointers. These + * tables are duplicated when additions are made (which means each + * table needs to be refcounted for the processes using it). When a new + * table is created, all the refcounters on the prog_list are bumped + * (to track each table that references the prog). When a new prog is + * added, it's just prepended to the list for the new table to point + * at. + * + * Manage all the possible errors before this step to not uselessly + * duplicate current_domain and avoid a rollback. + */ + if (!new_domain) { + /* + * If there is no Landlock domain used by the current task, + * then create a new one. + */ + new_domain = new_landlock_domain(); + if (IS_ERR(new_domain)) + goto put_tmp_lists; + } else if (refcount_read(¤t_domain->usage) > 1) { + /* + * If the current task is not the sole user of its Landlock + * domain, then duplicate it. + */ + new_domain = new_landlock_domain(); + if (IS_ERR(new_domain)) + goto put_tmp_lists; + for (i = 0; i < ARRAY_SIZE(new_domain->programs); i++) { + new_domain->programs[i] = + READ_ONCE(current_domain->programs[i]); + if (new_domain->programs[i]) + refcount_inc(&new_domain->programs[i]->usage); + } + + /* + * Landlock domain from the current task will not be freed here + * because the usage is strictly greater than 1. It is only + * prevented to be freed by another task thanks to the caller + * of landlock_prepend_prog() which should be locked if needed. + */ + landlock_put_domain(current_domain); + } + + /* prepend tmp_domain to new_domain */ + for (i = 0; i < ARRAY_SIZE(tmp_domain.programs); i++) { + /* get the last new list */ + struct landlock_prog_list *last_list = + tmp_domain.programs[i]; + + if (last_list) { + while (last_list->prev) + last_list = last_list->prev; + /* no need to increment usage (pointer replacement) */ + last_list->prev = new_domain->programs[i]; + new_domain->programs[i] = tmp_domain.programs[i]; + } + } + return new_domain; + +put_tmp_lists: + for (i = 0; i < ARRAY_SIZE(tmp_domain.programs); i++) + put_landlock_prog_list(tmp_domain.programs[i]); + return new_domain; +} diff --git a/security/landlock/domain_manage.h b/security/landlock/domain_manage.h new file mode 100644 index 000000000000..5b5b49f6e3e8 --- /dev/null +++ b/security/landlock/domain_manage.h @@ -0,0 +1,23 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - domain management headers + * + * Copyright © 2016-2019 Mickaël Salaün + * Copyright © 2018-2019 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_DOMAIN_MANAGE_H +#define _SECURITY_LANDLOCK_DOMAIN_MANAGE_H + +#include + +#include "common.h" + +void landlock_get_domain(struct landlock_domain *dom); +void landlock_put_domain(struct landlock_domain *dom); + +struct landlock_domain *landlock_prepend_prog( + struct landlock_domain *current_domain, + struct bpf_prog *prog); + +#endif /* _SECURITY_LANDLOCK_DOMAIN_MANAGE_H */