From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760938AbcINH02 (ORCPT ); Wed, 14 Sep 2016 03:26:28 -0400 Received: from smtp-sh.infomaniak.ch ([128.65.195.4]:45166 "EHLO smtp-sh.infomaniak.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759045AbcINH0V (ORCPT ); Wed, 14 Sep 2016 03:26:21 -0400 From: =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= To: linux-kernel@vger.kernel.org Cc: =?UTF-8?q?Micka=C3=ABl=20Sala=C3=BCn?= , Alexei Starovoitov , Andy Lutomirski , Arnd Bergmann , Casey Schaufler , Daniel Borkmann , Daniel Mack , David Drysdale , "David S . Miller" , Elena Reshetova , "Eric W . Biederman" , James Morris , Kees Cook , Paul Moore , Sargun Dhillon , "Serge E . Hallyn" , Tejun Heo , Will Drewry , kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org, linux-security-module@vger.kernel.org, netdev@vger.kernel.org, cgroups@vger.kernel.org Subject: [RFC v3 22/22] samples/landlock: Add sandbox example Date: Wed, 14 Sep 2016 09:24:15 +0200 Message-Id: <20160914072415.26021-23-mic@digikod.net> X-Mailer: git-send-email 2.9.3 In-Reply-To: <20160914072415.26021-1-mic@digikod.net> References: <20160914072415.26021-1-mic@digikod.net> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Antivirus: Dr.Web (R) for Unix mail servers drweb plugin ver.6.0.2.8 X-Antivirus-Code: 0x100000 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Add a basic sandbox tool to create a process isolated from some part of the system. This can depend of the current cgroup. Example with the current process hierarchy (seccomp): $ ls /home user1 $ LANDLOCK_ALLOWED='/bin:/lib:/usr:/tmp:/proc/self/fd/0' \ ./samples/landlock/sandbox /bin/sh -i Launching a new sandboxed process. $ ls /home ls: cannot open directory '/home': Permission denied Example with a cgroup: $ mkdir /sys/fs/cgroup/sandboxed $ ls /home user1 $ LANDLOCK_CGROUPS='/sys/fs/cgroup/sandboxed' \ LANDLOCK_ALLOWED='/bin:/lib:/usr:/tmp:/proc/self/fd/0' \ ./samples/landlock/sandbox Ready to sandbox with cgroups. $ ls /home user1 $ echo $$ > /sys/fs/cgroup/sandboxed/cgroup.procs $ ls /home ls: cannot open directory '/home': Permission denied Changes since v2: * use BPF_PROG_ATTACH for cgroup handling Signed-off-by: Mickaël Salaün Cc: Alexei Starovoitov Cc: Andy Lutomirski Cc: Daniel Borkmann Cc: David S. Miller Cc: James Morris Cc: Kees Cook Cc: Serge E. Hallyn --- samples/Makefile | 2 +- samples/landlock/.gitignore | 1 + samples/landlock/Makefile | 16 +++ samples/landlock/sandbox.c | 307 ++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 325 insertions(+), 1 deletion(-) create mode 100644 samples/landlock/.gitignore create mode 100644 samples/landlock/Makefile create mode 100644 samples/landlock/sandbox.c diff --git a/samples/Makefile b/samples/Makefile index 1a20169d85ac..a2dcd57ca7ac 100644 --- a/samples/Makefile +++ b/samples/Makefile @@ -2,4 +2,4 @@ obj-$(CONFIG_SAMPLES) += kobject/ kprobes/ trace_events/ livepatch/ \ hw_breakpoint/ kfifo/ kdb/ hidraw/ rpmsg/ seccomp/ \ - configfs/ connector/ v4l/ trace_printk/ + configfs/ connector/ v4l/ trace_printk/ landlock/ diff --git a/samples/landlock/.gitignore b/samples/landlock/.gitignore new file mode 100644 index 000000000000..f6c6da930a30 --- /dev/null +++ b/samples/landlock/.gitignore @@ -0,0 +1 @@ +/sandbox diff --git a/samples/landlock/Makefile b/samples/landlock/Makefile new file mode 100644 index 000000000000..d1044b2afd27 --- /dev/null +++ b/samples/landlock/Makefile @@ -0,0 +1,16 @@ +# kbuild trick to avoid linker error. Can be omitted if a module is built. +obj- := dummy.o + +hostprogs-$(CONFIG_SECURITY_LANDLOCK) := sandbox +sandbox-objs := sandbox.o + +always := $(hostprogs-y) + +HOSTCFLAGS += -I$(objtree)/usr/include + +# Trick to allow make to be run from this directory +all: + $(MAKE) -C ../../ $$PWD/ + +clean: + $(MAKE) -C ../../ M=$$PWD clean diff --git a/samples/landlock/sandbox.c b/samples/landlock/sandbox.c new file mode 100644 index 000000000000..9d6ac00cdd23 --- /dev/null +++ b/samples/landlock/sandbox.c @@ -0,0 +1,307 @@ +/* + * Landlock LSM - Sandbox example + * + * Copyright (C) 2016 Mickaël Salaün + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 3, as + * published by the Free Software Foundation. + */ + +#define _GNU_SOURCE +#include +#include /* open() */ +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "../../tools/include/linux/filter.h" + +#include "../bpf/libbpf.c" + +#ifndef seccomp +static int seccomp(unsigned int op, unsigned int flags, void *args) +{ + errno = 0; + return syscall(__NR_seccomp, op, flags, args); +} +#endif + +static int landlock_prog_load(const struct bpf_insn *insns, int prog_len, + enum landlock_hook_id hook_id, __u64 access) +{ + union bpf_attr attr = { + .prog_type = BPF_PROG_TYPE_LANDLOCK, + .insns = ptr_to_u64((void *) insns), + .insn_cnt = prog_len / sizeof(struct bpf_insn), + .license = ptr_to_u64((void *) "GPL"), + .log_buf = ptr_to_u64(bpf_log_buf), + .log_size = LOG_BUF_SIZE, + .log_level = 1, + .prog_subtype.landlock_hook = { + .id = hook_id, + .origin = LANDLOCK_FLAG_ORIGIN_SECCOMP | + LANDLOCK_FLAG_ORIGIN_SYSCALL | + LANDLOCK_FLAG_ORIGIN_INTERRUPT, + .access = access, + }, + }; + + /* assign one field outside of struct init to make sure any + * padding is zero initialized + */ + attr.kern_version = 0; + + bpf_log_buf[0] = 0; + + return syscall(__NR_bpf, BPF_PROG_LOAD, &attr, sizeof(attr)); +} + +#define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0])) + +static int apply_sandbox(const char **allowed_paths, int path_nb, const char + **cgroup_paths, int cgroup_nb) +{ + __u32 key; + int i, ret = 0, map_fs = -1, offset; + + /* set up the test sandbox */ + if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) { + perror("prctl(no_new_priv)"); + return 1; + } + + /* register a new syscall filter */ + struct sock_filter filter0[] = { + /* pass a cookie containing 5 to the LSM hook filter */ + BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_LANDLOCK | 5), + }; + struct sock_fprog prog0 = { + .len = (unsigned short)ARRAY_SIZE(filter0), + .filter = filter0, + }; + if (!cgroup_nb) { + if (seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog0)) { + perror("seccomp(set_filter)"); + return 1; + } + } + + if (path_nb) { + map_fs = bpf_create_map(BPF_MAP_TYPE_LANDLOCK_ARRAY, + sizeof(key), sizeof(struct landlock_handle), + 10, 0); + if (map_fs < 0) { + fprintf(stderr, "bpf_create_map(fs): %s\n", + strerror(errno)); + return 1; + } + for (key = 0; key < path_nb; key++) { + int fd = open(allowed_paths[key], + O_RDONLY | O_CLOEXEC); + if (fd < 0) { + fprintf(stderr, "open(fs: \"%s\"): %s\n", + allowed_paths[key], + strerror(errno)); + return 1; + } + struct landlock_handle handle = { + .type = BPF_MAP_HANDLE_TYPE_LANDLOCK_FS_FD, + .fd = (__u64)fd, + }; + + /* register a new LSM handle */ + if (bpf_update_elem(map_fs, &key, &handle, BPF_ANY)) { + fprintf(stderr, "bpf_update_elem(fs: \"%s\"): %s\n", + allowed_paths[key], + strerror(errno)); + close(fd); + return 1; + } + close(fd); + } + } + + /* load a LSM filter hook (eBPF) */ + struct bpf_insn hook_pre[] = { + /* save context */ + BPF_MOV64_REG(BPF_REG_6, BPF_REG_1), + +#if 0 + /* check our cookie (not used in this example) */ + BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_6, offsetof(struct + landlock_data, cookie)), + BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 5, 2), + BPF_MOV32_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), +#endif + }; + struct bpf_insn hook_path[] = { + /* specify an option, if any */ + BPF_MOV32_IMM(BPF_REG_1, 0), + /* handles to compare with */ + BPF_LD_MAP_FD(BPF_REG_2, map_fs), + BPF_MOV64_IMM(BPF_REG_3, BPF_MAP_ARRAY_OP_OR), + /* hook argument (struct file) */ + BPF_LDX_MEM(BPF_DW, BPF_REG_4, BPF_REG_6, offsetof(struct + landlock_data, args[0])), + /* checker function */ + BPF_EMIT_CALL(BPF_FUNC_landlock_cmp_fs_beneath_with_struct_file), + + /* if the checked path is beneath the handle */ + BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 2), + BPF_MOV32_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + /* allow anonymous mapping */ + BPF_JMP_IMM(BPF_JNE, BPF_REG_0, -ENOENT, 2), + BPF_MOV32_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + /* deny by default, if any error */ + BPF_JMP_IMM(BPF_JGE, BPF_REG_0, 0, 2), + BPF_MOV32_IMM(BPF_REG_0, EACCES), + BPF_EXIT_INSN(), + }; + struct bpf_insn hook_post[] = { + BPF_MOV32_IMM(BPF_REG_0, EACCES), + BPF_EXIT_INSN(), + }; + + unsigned long hook_size = sizeof(hook_pre) + sizeof(hook_path) * + (path_nb ? 1 : 0) + sizeof(hook_post); + + struct bpf_insn *hook0 = malloc(hook_size); + if (!hook0) { + perror("malloc"); + ret = 1; + goto err_alloc; + } + memcpy(hook0, hook_pre, sizeof(hook_pre)); + offset = sizeof(hook_pre) / sizeof(hook0[0]); + if (path_nb) { + memcpy(hook0 + offset, hook_path, sizeof(hook_path)); + offset += sizeof(hook_path) / sizeof(hook0[0]); + } + memcpy(hook0 + offset, hook_post, sizeof(hook_post)); + + /* TODO: handle inode_permission hook (e.g. chdir) */ + enum landlock_hook_id hooks[] = { + LANDLOCK_HOOK_FILE_OPEN, + LANDLOCK_HOOK_FILE_PERMISSION, + LANDLOCK_HOOK_MMAP_FILE, + }; + for (i = 0; i < ARRAY_SIZE(hooks) && !ret; i++) { + int bpf0 = landlock_prog_load(hook0, hook_size, hooks[i], 0); + if (bpf0 == -1) { + perror("prog_load"); + fprintf(stderr, "%s", bpf_log_buf); + ret = 1; + break; + } + if (!cgroup_nb) { + if (seccomp(SECCOMP_SET_LANDLOCK_HOOK, 0, &bpf0)) { + perror("seccomp(set_hook)"); + ret = 1; + } + } else { + for (key = 0; key < cgroup_nb && !ret; key++) { + int fd = open(cgroup_paths[key], + O_DIRECTORY | O_CLOEXEC); + if (fd < 0) { + fprintf(stderr, "open(cgroup: \"%s\"): %s\n", + cgroup_paths[key], strerror(errno)); + ret = 1; + break; + } + if (bpf_prog_attach(bpf0, fd, BPF_CGROUP_LANDLOCK)) { + fprintf(stderr, "bpf_prog_attach(cgroup: \"%s\"): %s\n", + cgroup_paths[key], strerror(errno)); + ret = 1; + } + close(fd); + } + } + close(bpf0); + } + + free(hook0); +err_alloc: + if (path_nb) { + close(map_fs); + } + return ret; +} + +#define ENV_FS_PATH_NAME "LANDLOCK_ALLOWED" +#define ENV_CGROUP_PATH_NAME "LANDLOCK_CGROUPS" +#define ENV_PATH_TOKEN ":" + +static int parse_path(char *env_path, const char ***path_list) +{ + int i, path_nb = 0; + + if (env_path) { + path_nb++; + for (i = 0; env_path[i]; i++) { + if (env_path[i] == ENV_PATH_TOKEN[0]) { + path_nb++; + } + } + } + *path_list = malloc(path_nb * sizeof(**path_list)); + for (i = 0; i < path_nb; i++) { + (*path_list)[i] = strsep(&env_path, ENV_PATH_TOKEN); + } + + return path_nb; +} + +int main(int argc, char * const argv[], char * const *envp) +{ + char *cmd_path; + char *env_path_allowed, *env_path_cgroup; + int path_nb, cgroup_nb; + const char **sb_paths = NULL; + const char **cg_paths = NULL; + char * const *cmd_argv; + + env_path_allowed = getenv(ENV_FS_PATH_NAME); + if (env_path_allowed) + env_path_allowed = strdup(env_path_allowed); + env_path_cgroup = getenv(ENV_CGROUP_PATH_NAME); + if (env_path_cgroup) + env_path_cgroup = strdup(env_path_cgroup); + + path_nb = parse_path(env_path_allowed, &sb_paths); + cgroup_nb = parse_path(env_path_cgroup, &cg_paths); + if (argc < 2 && !cgroup_nb) { + fprintf(stderr, "usage: %s [args]...\n\n", argv[0]); + fprintf(stderr, "Environment variables containing paths, each separated by a colon:\n"); + fprintf(stderr, "* %s (whitelist of allowed files and directories)\n", + ENV_FS_PATH_NAME); + fprintf(stderr, "* %s (optional cgroup paths for which the sandbox is enabled)\n", + ENV_CGROUP_PATH_NAME); + fprintf(stderr, "\nexample:\n%s='/bin:/lib:/usr:/tmp:/proc/self/fd/0' %s /bin/sh -i\n", + ENV_FS_PATH_NAME, argv[0]); + return 1; + } + if (apply_sandbox(sb_paths, path_nb, cg_paths, cgroup_nb)) + return 1; + if (!cgroup_nb) { + cmd_path = argv[1]; + cmd_argv = argv + 1; + fprintf(stderr, "Launching a new sandboxed process.\n"); + execve(cmd_path, cmd_argv, envp); + perror("execve"); + return 1; + } + fprintf(stderr, "Ready to sandbox with cgroups.\n"); + return 0; +} -- 2.9.3