[kernel-hardening] [PATCH v5 07/10] bpf: Add a Landlock sandbox example

Mickaël Salaün
2017-02-22T01:26:29Z

Add a basic sandbox tool to create a process isolated from some part of
the system. This sandbox create a read-only environment. It is only
allowed to write to a character device such as a TTY:

# :> X
# echo $?
0
# ./samples/bpf/landlock1 /bin/sh -i
Launching a new sandboxed process.
# :> Y
cannot create Y: Operation not permitted

Changes since v4:
* write Landlock rule in C and compiled it with LLVM
* remove cgroup handling
* remove path handling: only handle a read-only environment
* remove errno return codes

Changes since v3:
* remove seccomp and origin field: completely free from seccomp programs
* handle more FS-related hooks
* handle inode hooks and directory traversal
* add faked but consistent view thanks to ENOENT
* add /lib64 in the example
* fix spelling
* rename some types and definitions (e.g. SECCOMP_ADD_LANDLOCK_RULE)

Changes since v2:
* use BPF_PROG_ATTACH for cgroup handling

Signed-off-by: Mickaël Salaün <mic@digikod.net>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: James Morris <james.l.morris@oracle.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Serge E. Hallyn <serge@hallyn.com>
---
samples/bpf/.gitignore | 32 ++++++++++++++
samples/bpf/Makefile | 4 ++
samples/bpf/bpf_load.c | 26 +++++++++--
samples/bpf/landlock1_kern.c | 46 +++++++++++++++++++
samples/bpf/landlock1_user.c | 102 +++++++++++++++++++++++++++++++++++++++++++
5 files changed, 206 insertions(+), 4 deletions(-)
create mode 100644 samples/bpf/.gitignore
create mode 100644 samples/bpf/landlock1_kern.c
create mode 100644 samples/bpf/landlock1_user.c

diff --git a/samples/bpf/.gitignore b/samples/bpf/.gitignore
new file mode 100644
index 000000000000..a7562a5ef4c2
--- /dev/null
+++ b/samples/bpf/.gitignore
@@ -0,0 +1,32 @@
+fds_example
+lathist
+lwt_len_hist
+map_perf_test
+offwaketime
+sampleip
+sockex1
+sockex2
+sockex3
+sock_example
+spintest
+tc_l2_redirect
+test_cgrp2_array_pin
+test_cgrp2_attach
+test_cgrp2_attach2
+test_cgrp2_sock
+test_cgrp2_sock2
+test_current_task_under_cgroup
+test_lru_dist
+test_overhead
+test_probe_write_user
+trace_event
+trace_output
+tracex1
+tracex2
+tracex3
+tracex4
+tracex5
+tracex6
+xdp1
+xdp2
+xdp_tx_iptunnel
diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 09e9d535bd74..3d3afd709635 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -34,6 +34,7 @@ hostprogs-y += sampleip
hostprogs-y += tc_l2_redirect
hostprogs-y += lwt_len_hist
hostprogs-y += xdp_tx_iptunnel
+hostprogs-y += landlock1

# Libbpf dependencies
LIBBPF := ../../tools/lib/bpf/bpf.o
@@ -72,6 +73,7 @@ sampleip-objs := bpf_load.o $(LIBBPF) sampleip_user.o
tc_l2_redirect-objs := bpf_load.o $(LIBBPF) tc_l2_redirect_user.o
lwt_len_hist-objs := bpf_load.o $(LIBBPF) lwt_len_hist_user.o
xdp_tx_iptunnel-objs := bpf_load.o $(LIBBPF) xdp_tx_iptunnel_user.o
+landlock1-objs := bpf_load.o $(LIBBPF) landlock1_user.o

# Tell kbuild to always build the programs
always := $(hostprogs-y)
@@ -105,6 +107,7 @@ always += trace_event_kern.o
always += sampleip_kern.o
always += lwt_len_hist_kern.o
always += xdp_tx_iptunnel_kern.o
+always += landlock1_kern.o

HOSTCFLAGS += -I$(objtree)/usr/include
HOSTCFLAGS += -I$(srctree)/tools/lib/
@@ -139,6 +142,7 @@ HOSTLOADLIBES_sampleip += -lelf
HOSTLOADLIBES_tc_l2_redirect += -l elf
HOSTLOADLIBES_lwt_len_hist += -l elf
HOSTLOADLIBES_xdp_tx_iptunnel += -lelf
+HOSTLOADLIBES_landlock1 += -lelf

# Allows pointing LLC/CLANG to a LLVM backend with bpf support, redefine on cmdline:
# make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
diff --git a/samples/bpf/bpf_load.c b/samples/bpf/bpf_load.c
index d23dc13ab0f2..78df39cf8b2f 100644
--- a/samples/bpf/bpf_load.c
+++ b/samples/bpf/bpf_load.c
@@ -68,6 +68,7 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
bool is_perf_event = strncmp(event, "perf_event", 10) == 0;
bool is_cgroup_skb = strncmp(event, "cgroup/skb", 10) == 0;
bool is_cgroup_sk = strncmp(event, "cgroup/sock", 11) == 0;
+ bool is_landlock = strncmp(event, "landlock", 8) == 0;
size_t insns_cnt = size / sizeof(struct bpf_insn);
enum bpf_prog_type prog_type;
char buf[256];
@@ -93,6 +94,12 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
prog_type = BPF_PROG_TYPE_CGROUP_SKB;
} else if (is_cgroup_sk) {
prog_type = BPF_PROG_TYPE_CGROUP_SOCK;
+ } else if (is_landlock) {
+ prog_type = BPF_PROG_TYPE_LANDLOCK;
+ if (!subtype.landlock_rule.event) {
+ printf("No subtype\n");
+ return -1;
+ }
} else {
printf("Unknown event '%s'\n", event);
return -1;
@@ -107,7 +114,7 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size)

prog_fd[prog_cnt++] = fd;

- if (is_xdp || is_perf_event || is_cgroup_skb || is_cgroup_sk)
+ if (is_xdp || is_perf_event || is_cgroup_skb || is_cgroup_sk || is_landlock)
return 0;

if (is_socket) {
@@ -278,6 +285,8 @@ int load_bpf_file(char *path)
Elf_Data *data, *data_prog, *symbols = NULL;
char *shname, *shname_prog;

+ subtype.landlock_rule.event = 0;
+
if (elf_version(EV_CURRENT) == EV_NONE)
return 1;

@@ -322,6 +331,14 @@ int load_bpf_file(char *path)
processed_sec[i] = true;
if (load_maps(data->d_buf, data->d_size))
return 1;
+ } else if (strcmp(shname, "subtype") == 0) {
+ processed_sec[i] = true;
+ if (data->d_size != sizeof(union bpf_prog_subtype)) {
+ printf("invalid size of subtype section %zd\n",
+ data->d_size);
+ return 1;
+ }
+ memcpy(&subtype, data->d_buf, sizeof(union bpf_prog_subtype));
} else if (shdr.sh_type == SHT_SYMTAB) {
symbols = data;
}
@@ -357,14 +374,14 @@ int load_bpf_file(char *path)
memcmp(shname_prog, "xdp", 3) == 0 ||
memcmp(shname_prog, "perf_event", 10) == 0 ||
memcmp(shname_prog, "socket", 6) == 0 ||
- memcmp(shname_prog, "cgroup/", 7) == 0)
+ memcmp(shname_prog, "cgroup/", 7) == 0 ||
+ memcmp(shname_prog, "landlock", 8) == 0)
load_and_attach(shname_prog, insns, data_prog->d_size);
}
}

/* load programs that don't use maps */
for (i = 1; i < ehdr.e_shnum; i++) {
-
if (processed_sec[i])
continue;

@@ -377,7 +394,8 @@ int load_bpf_file(char *path)
memcmp(shname, "xdp", 3) == 0 ||
memcmp(shname, "perf_event", 10) == 0 ||
memcmp(shname, "socket", 6) == 0 ||
- memcmp(shname, "cgroup/", 7) == 0)
+ memcmp(shname, "cgroup/", 7) == 0 ||
+ memcmp(shname, "landlock", 8) == 0)
load_and_attach(shname, data->d_buf, data->d_size);
}

diff --git a/samples/bpf/landlock1_kern.c b/samples/bpf/landlock1_kern.c
new file mode 100644
index 000000000000..ff23061e6324
--- /dev/null
+++ b/samples/bpf/landlock1_kern.c
@@ -0,0 +1,46 @@
+/*
+ * Landlock LSM - Sample 1 (BPF program)
+ *
+ * Copyright © 2017 Mickaël Salaün <mic@digikod.net>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ */
+
+#define KBUILD_MODNAME "foo"
+#include <uapi/linux/bpf.h>
+#include <uapi/linux/stat.h> /* S_ISCHR() */
+#include "bpf_helpers.h"
+
+SEC("landlock1")
+static int landlock_fs_prog1(struct landlock_context *ctx)
+{
+ char fmt_error[] = "landlock1: error: get_mode:%lld\n";
+ char fmt_name[] = "landlock1: syscall:%d\n";
+ long long ret;
+
+ if (!(ctx->arg2 & LANDLOCK_ACTION_FS_WRITE))
+ return 0;
+ ret = bpf_handle_fs_get_mode((void *)ctx->arg1);
+ if (ret < 0) {
+ bpf_trace_printk(fmt_error, sizeof(fmt_error), ret);
+ return 1;
+ }
+ if (S_ISCHR(ret))
+ return 0;
+ bpf_trace_printk(fmt_name, sizeof(fmt_name), ctx->syscall_nr);
+ return 1;
+}
+
+SEC("subtype")
+static union bpf_prog_subtype _subtype = {
+ .landlock_rule = {
+ .version = 1,
+ .event = LANDLOCK_SUBTYPE_EVENT_FS,
+ .ability = LANDLOCK_SUBTYPE_ABILITY_DEBUG,
+ }
+};
+
+SEC("license")
+static char _license[] = "GPL";
diff --git a/samples/bpf/landlock1_user.c b/samples/bpf/landlock1_user.c
new file mode 100644
index 000000000000..5feb660caed4
--- /dev/null
+++ b/samples/bpf/landlock1_user.c
@@ -0,0 +1,102 @@
+/*
+ * Landlock LSM - Sample 1 (userland)
+ *
+ * Copyright © 2017 Mickaël Salaün <mic@digikod.net>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ */
+
+#include "bpf_load.h"
+#include "libbpf.h"
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h> /* open() */
+#include <linux/bpf.h>
+#include <linux/filter.h>
+#include <linux/prctl.h>
+#include <linux/seccomp.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/prctl.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#ifndef seccomp
+static int seccomp(unsigned int op, unsigned int flags, void *args)
+{
+ errno = 0;
+ return syscall(__NR_seccomp, op, flags, args);
+}
+#endif
+
+#define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0]))
+#define MAX_ERRNO 4095
+
+
+struct landlock_rule {
+ enum landlock_subtype_event event;
+ struct bpf_insn *bpf;
+ size_t size;
+};
+
+static int apply_sandbox(int prog_fd)
+{
+ int ret = 0;
+
+ /* set up the test sandbox */
+ if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
+ perror("prctl(no_new_priv)");
+ return 1;
+ }
+ if (seccomp(SECCOMP_ADD_LANDLOCK_RULE, 0, &prog_fd)) {
+ perror("seccomp(set_hook)");
+ ret = 1;
+ }
+ close(prog_fd);
+
+ return ret;
+}
+
+int main(int argc, char * const argv[], char * const *envp)
+{
+ char filename[256];
+ char *cmd_path;
+ char * const *cmd_argv;
+
+ if (argc < 2) {
+ fprintf(stderr, "usage: %s <cmd> [args]...\n\n", argv[0]);
+ fprintf(stderr, "Launch a command in a read-only environment "
+ "(except for character devices).\n");
+ fprintf(stderr, "Display debug with: "
+ "cat /sys/kernel/debug/tracing/trace_pipe &\n");
+ return 1;
+ }
+
+ snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+ if (load_bpf_file(filename)) {
+ printf("%s", bpf_log_buf);
+ return 1;
+ }
+ if (!prog_fd[0]) {
+ if (errno) {
+ printf("load_bpf_file: %s\n", strerror(errno));
+ } else {
+ printf("load_bpf_file: Error\n");
+ }
+ return 1;
+ }
+
+ if (apply_sandbox(prog_fd[0]))
+ return 1;
+ 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;
+}
--
2.11.0