Add a first Landlock hook that can be used to enforce a security policy or to audit some process activities. For a sandboxing use-case, it is needed to inform the kernel if a task can legitimately debug another. ptrace(2) can also be used by an attacker to impersonate another task and remain undetected while performing malicious activities. Using ptrace(2) and related features on a target process can lead to a privilege escalation. A sandboxed task must then be able to tell the kernel if another task is more privileged, via ptrace_may_access(). 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 v10: * revamp and replace the static policy with a Landlock hook which may be used by the corresponding BPF_LANDLOCK_PTRACE program (attach) type and a dedicated process_cmp_landlock_ptrace() BPF helper * check prog return value against LANDLOCK_RET_DENY (ret is a bitmask) Changes since v6: * factor out ptrace check * constify pointers * cleanup headers * use the new security_add_hooks() --- security/landlock/Makefile | 4 +- security/landlock/bpf_run.c | 62 +++++++++++++++++ security/landlock/bpf_run.h | 25 +++++++ security/landlock/hooks_ptrace.c | 114 +++++++++++++++++++++++++++++++ security/landlock/hooks_ptrace.h | 19 ++++++ security/landlock/init.c | 2 + 6 files changed, 224 insertions(+), 2 deletions(-) create mode 100644 security/landlock/bpf_run.c create mode 100644 security/landlock/bpf_run.h create mode 100644 security/landlock/hooks_ptrace.c create mode 100644 security/landlock/hooks_ptrace.h diff --git a/security/landlock/Makefile b/security/landlock/Makefile index 0b291f2c027c..93e4c2f31c8a 100644 --- a/security/landlock/Makefile +++ b/security/landlock/Makefile @@ -1,6 +1,6 @@ obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o landlock-y := init.o \ - bpf_verify.o bpf_ptrace.o \ + bpf_verify.o bpf_run.o bpf_ptrace.o \ domain_manage.o domain_syscall.o \ - hooks_cred.o + hooks_cred.o hooks_ptrace.o diff --git a/security/landlock/bpf_run.c b/security/landlock/bpf_run.c new file mode 100644 index 000000000000..8874958bdc30 --- /dev/null +++ b/security/landlock/bpf_run.c @@ -0,0 +1,62 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - eBPF program evaluation + * + * Copyright © 2016-2019 Mickaël Salaün <mic@xxxxxxxxxxx> + * Copyright © 2018-2019 ANSSI + */ + +#include <asm/current.h> +#include <linux/bpf.h> +#include <linux/errno.h> +#include <linux/filter.h> +#include <linux/rculist.h> +#include <uapi/linux/landlock.h> + +#include "bpf_run.h" +#include "common.h" +#include "hooks_ptrace.h" + +static const void *get_prog_ctx(struct landlock_hook_ctx *hook_ctx) +{ + switch (hook_ctx->type) { + case LANDLOCK_HOOK_PTRACE: + return landlock_get_ctx_ptrace(hook_ctx->ctx_ptrace); + } + WARN_ON(1); + return NULL; +} + +/** + * landlock_access_denied - run Landlock programs tied to a hook + * + * @domain: Landlock domain pointer + * @hook_ctx: non-NULL valid eBPF context pointer + * + * Return true if at least one program return deny, false otherwise. + */ +bool landlock_access_denied(struct landlock_domain *domain, + struct landlock_hook_ctx *hook_ctx) +{ + struct landlock_prog_list *prog_list; + const size_t hook = get_hook_index(hook_ctx->type); + + if (!domain) + return false; + + for (prog_list = domain->programs[hook]; prog_list; + prog_list = prog_list->prev) { + u32 ret; + const void *prog_ctx; + + prog_ctx = get_prog_ctx(hook_ctx); + if (!prog_ctx || WARN_ON(IS_ERR(prog_ctx))) + return true; + rcu_read_lock(); + ret = BPF_PROG_RUN(prog_list->prog, prog_ctx); + rcu_read_unlock(); + if (ret & LANDLOCK_RET_DENY) + return true; + } + return false; +} diff --git a/security/landlock/bpf_run.h b/security/landlock/bpf_run.h new file mode 100644 index 000000000000..3461cbb8ec12 --- /dev/null +++ b/security/landlock/bpf_run.h @@ -0,0 +1,25 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - eBPF program evaluation headers + * + * Copyright © 2016-2019 Mickaël Salaün <mic@xxxxxxxxxxx> + * Copyright © 2018-2019 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_BPF_RUN_H +#define _SECURITY_LANDLOCK_BPF_RUN_H + +#include "common.h" +#include "hooks_ptrace.h" + +struct landlock_hook_ctx { + enum landlock_hook_type type; + union { + struct landlock_hook_ctx_ptrace *ctx_ptrace; + }; +}; + +bool landlock_access_denied(struct landlock_domain *domain, + struct landlock_hook_ctx *hook_ctx); + +#endif /* _SECURITY_LANDLOCK_BPF_RUN_H */ diff --git a/security/landlock/hooks_ptrace.c b/security/landlock/hooks_ptrace.c new file mode 100644 index 000000000000..8e518a472d04 --- /dev/null +++ b/security/landlock/hooks_ptrace.c @@ -0,0 +1,114 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - ptrace hooks + * + * Copyright © 2017-2019 Mickaël Salaün <mic@xxxxxxxxxxx> + * Copyright © 2019 ANSSI + */ + +#include <asm/current.h> +#include <linux/cred.h> +#include <linux/errno.h> +#include <linux/kernel.h> +#include <linux/lsm_hooks.h> +#include <linux/sched.h> +#include <uapi/linux/landlock.h> + +#include "bpf_run.h" +#include "common.h" +#include "hooks_ptrace.h" + +struct landlock_hook_ctx_ptrace { + struct landlock_context_ptrace prog_ctx; +}; + +const struct landlock_context_ptrace *landlock_get_ctx_ptrace( + const struct landlock_hook_ctx_ptrace *hook_ctx) +{ + if (WARN_ON(!hook_ctx)) + return NULL; + + return &hook_ctx->prog_ctx; +} + +static int check_ptrace(struct landlock_domain *domain, + struct task_struct *tracer, struct task_struct *tracee) +{ + struct landlock_hook_ctx_ptrace ctx_ptrace = { + .prog_ctx = { + .tracer = (uintptr_t)tracer, + .tracee = (uintptr_t)tracee, + }, + }; + struct landlock_hook_ctx hook_ctx = { + .type = LANDLOCK_HOOK_PTRACE, + .ctx_ptrace = &ctx_ptrace, + }; + + return landlock_access_denied(domain, &hook_ctx) ? -EPERM : 0; +} + +/** + * hook_ptrace_access_check - determine whether the current process may access + * another + * + * @child: the process to be accessed + * @mode: the mode of attachment + * + * If the current task (i.e. tracer) has one or multiple BPF_LANDLOCK_PTRACE + * programs, then run them with the `struct landlock_context_ptrace` context. + * If one of these programs return LANDLOCK_RET_DENY, then deny access with + * -EPERM, else allow it by returning 0. + */ +static int hook_ptrace_access_check(struct task_struct *child, + unsigned int mode) +{ + struct landlock_domain *dom_current; + const size_t hook = get_hook_index(LANDLOCK_HOOK_PTRACE); + + dom_current = landlock_cred(current_cred())->domain; + if (!(dom_current && dom_current->programs[hook])) + return 0; + return check_ptrace(dom_current, current, child); +} + +/** + * hook_ptrace_traceme - determine whether another process may trace the + * current one + * + * @parent: the task proposed to be the tracer + * + * If the parent task (i.e. tracer) has one or multiple BPF_LANDLOCK_PTRACE + * programs, then run them with the `struct landlock_context_ptrace` context. + * If one of these programs return LANDLOCK_RET_DENY, then deny access with + * -EPERM, else allow it by returning 0. + */ +static int hook_ptrace_traceme(struct task_struct *parent) +{ + struct landlock_domain *dom_parent; + const size_t hook = get_hook_index(LANDLOCK_HOOK_PTRACE); + int ret; + + rcu_read_lock(); + dom_parent = landlock_cred(__task_cred(parent))->domain; + if (!(dom_parent && dom_parent->programs[hook])) { + ret = 0; + goto put_rcu; + } + ret = check_ptrace(dom_parent, parent, current); + +put_rcu: + rcu_read_unlock(); + return ret; +} + +static struct security_hook_list landlock_hooks[] = { + LSM_HOOK_INIT(ptrace_access_check, hook_ptrace_access_check), + LSM_HOOK_INIT(ptrace_traceme, hook_ptrace_traceme), +}; + +__init void landlock_add_hooks_ptrace(void) +{ + security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks), + LANDLOCK_NAME); +} diff --git a/security/landlock/hooks_ptrace.h b/security/landlock/hooks_ptrace.h new file mode 100644 index 000000000000..53fe651bdb3e --- /dev/null +++ b/security/landlock/hooks_ptrace.h @@ -0,0 +1,19 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - ptrace hooks headers + * + * Copyright © 2017-2019 Mickaël Salaün <mic@xxxxxxxxxxx> + * Copyright © 2019 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_HOOKS_PTRACE_H +#define _SECURITY_LANDLOCK_HOOKS_PTRACE_H + +struct landlock_hook_ctx_ptrace; + +const struct landlock_context_ptrace *landlock_get_ctx_ptrace( + const struct landlock_hook_ctx_ptrace *hook_ctx); + +__init void landlock_add_hooks_ptrace(void); + +#endif /* _SECURITY_LANDLOCK_HOOKS_PTRACE_H */ diff --git a/security/landlock/init.c b/security/landlock/init.c index 8836ec4defd3..541aad17418e 100644 --- a/security/landlock/init.c +++ b/security/landlock/init.c @@ -10,11 +10,13 @@ #include "common.h" #include "hooks_cred.h" +#include "hooks_ptrace.h" static int __init landlock_init(void) { pr_info(LANDLOCK_NAME ": Registering hooks\n"); landlock_add_hooks_cred(); + landlock_add_hooks_ptrace(); return 0; } -- 2.23.0