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 <mic@xxxxxxxxxxx> Cc: Alexei Starovoitov <ast@xxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Cc: James Morris <jmorris@xxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Serge E. Hallyn <serge@xxxxxxxxxx> Cc: Will Drewry <wad@xxxxxxxxxxxx> --- Changes since v12: * move the landlock_put_domain() call from landlock_prepend_prog() to domain_syscall.c:landlock_seccomp_prepend_prog() (next commit): keep the same semantic but don't conditionally own the domain (safeguard domain owning) * always copy a domain to-be-modified which guarantee domain immutability: the callers of landlock_prepend_prog() are now fully in charge of concurrency handling, which is currently only handled by prepare_creds() and commit_creds() (next commit) * simplify landlock_prepend_prog() * use a consistent naming Changes since v11: * remove old code from previous refactoring (removing the program chaining concept) and simplify program prepending (reported by Serge E. Hallyn): * simplify landlock_prepend_prog() and merge it with store_landlock_prog() * add new_prog_list() and rework new_landlock_domain() * remove the extra page allocation checks, only rely on the eBPF program checks * replace the -EINVAL for the duplicate program check with the -EEXIST 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 | 152 ++++++++++++++++++++++++++++++ security/landlock/domain_manage.h | 22 +++++ 4 files changed, 214 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 <linux/bpf.h> #include <linux/filter.h> +#include <linux/refcount.h> 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..b65960611d09 --- /dev/null +++ b/security/landlock/domain_manage.c @@ -0,0 +1,152 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - domain management + * + * Copyright © 2016-2019 Mickaël Salaün <mic@xxxxxxxxxxx> + * Copyright © 2018-2019 ANSSI + */ + +#include <linux/err.h> +#include <linux/errno.h> +#include <linux/refcount.h> +#include <linux/slab.h> +#include <linux/spinlock.h> + +#include "common.h" +#include "domain_manage.h" + +void landlock_get_domain(struct landlock_domain *domain) +{ + if (!domain) + return; + refcount_inc(&domain->usage); +} + +static void put_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_prog_list(domain->programs[i]); + kfree(domain); + } +} + +static struct landlock_prog_list *create_prog_list(struct bpf_prog *prog) +{ + struct landlock_prog_list *new_list; + + if (WARN_ON(IS_ERR_OR_NULL(prog))) + return ERR_PTR(-EFAULT); + if (prog->type != BPF_PROG_TYPE_LANDLOCK_HOOK) + return ERR_PTR(-EINVAL); + prog = bpf_prog_inc(prog); + if (IS_ERR(prog)) + return ERR_CAST(prog); + new_list = kzalloc(sizeof(*new_list), GFP_KERNEL); + if (!new_list) { + bpf_prog_put(prog); + return ERR_PTR(-ENOMEM); + } + new_list->prog = prog; + refcount_set(&new_list->usage, 1); + return new_list; +} + +static struct landlock_domain *create_domain(struct bpf_prog *prog) +{ + struct landlock_domain *new_dom; + struct landlock_prog_list *new_list; + size_t hook; + + /* programs[] filled with NULL values */ + new_dom = kzalloc(sizeof(*new_dom), GFP_KERNEL); + if (!new_dom) + return ERR_PTR(-ENOMEM); + refcount_set(&new_dom->usage, 1); + new_list = create_prog_list(prog); + if (IS_ERR(new_list)) { + kfree(new_dom); + return ERR_CAST(new_list); + } + hook = get_hook_index(get_hook_type(prog)); + new_dom->programs[hook] = new_list; + return new_dom; +} + +/** + * landlock_prepend_prog - extend a Landlock domain with an eBPF program + * + * Prepend @prog to @domain if @prog is not already in @domain. + * + * @domain: domain to copy and extend with @prog. This domain must not be + * modified by another function than this one to guarantee domain + * immutability. + * @prog: non-NULL Landlock program to prepend to a copy of @domain. @prog + * will be owned by landlock_prepend_prog(). You can then call + * bpf_prog_put(@prog) after. + * + * Return a copy of @domain (with @prog prepended) when OK. Return a pointer + * error otherwise. + */ +struct landlock_domain *landlock_prepend_prog(struct landlock_domain *domain, + struct bpf_prog *prog) +{ + struct landlock_prog_list *walker; + struct landlock_domain *new_dom; + size_t i, hook; + + if (WARN_ON(!prog)) + return ERR_PTR(-EFAULT); + if (prog->type != BPF_PROG_TYPE_LANDLOCK_HOOK) + return ERR_PTR(-EINVAL); + + if (!domain) + return create_domain(prog); + + hook = get_hook_index(get_hook_type(prog)); + /* check for similar program */ + for (walker = domain->programs[hook]; walker; + walker = walker->prev) { + /* don't allow duplicate programs */ + if (prog == walker->prog) + return ERR_PTR(-EEXIST); + } + + new_dom = create_domain(prog); + if (IS_ERR(new_dom)) + return new_dom; + + /* copy @domain (which is guarantee to be immutable) */ + for (i = 0; i < ARRAY_SIZE(new_dom->programs); i++) { + struct landlock_prog_list *current_list; + struct landlock_prog_list **new_list; + + current_list = domain->programs[i]; + if (!current_list) + continue; + refcount_inc(¤t_list->usage); + new_list = &new_dom->programs[i]; + if (*new_list) + new_list = &(*new_list)->prev; + /* do not increment usage */ + *new_list = current_list; + } + return new_dom; +} diff --git a/security/landlock/domain_manage.h b/security/landlock/domain_manage.h new file mode 100644 index 000000000000..d32c65c941c0 --- /dev/null +++ b/security/landlock/domain_manage.h @@ -0,0 +1,22 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - domain management headers + * + * Copyright © 2016-2019 Mickaël Salaün <mic@xxxxxxxxxxx> + * Copyright © 2018-2019 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_DOMAIN_MANAGE_H +#define _SECURITY_LANDLOCK_DOMAIN_MANAGE_H + +#include <linux/filter.h> + +#include "common.h" + +void landlock_get_domain(struct landlock_domain *domain); +void landlock_put_domain(struct landlock_domain *domain); + +struct landlock_domain *landlock_prepend_prog(struct landlock_domain *domain, + struct bpf_prog *prog); + +#endif /* _SECURITY_LANDLOCK_DOMAIN_MANAGE_H */ -- 2.23.0