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Subject[PATCH bpf-next v9 08/10] bpf: Add a Landlock sandbox example
Date
Add a basic sandbox tool to launch a command which is denied access to a
list of files and directories.

Add to the bpf_load library the ability to handle a BPF program subtype.

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 <jmorris@namei.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Serge E. Hallyn <serge@hallyn.com>
---

Changes since v8:
* rewrite the landlock1 sample which deny access to a set of files or
directories (i.e. simple blacklist) to fit with the previous patches
* add "landlock1" to .gitignore
* in bpf_load.c, pass the subtype with a call to
bpf_load_program_xattr()

Changes since v7:
* rewrite the example using an inode map
* add to bpf_load the ability to handle subtypes per program type

Changes since v6:
* check return value of load_and_attach()
* allow to write on pipes
* rename BPF_PROG_TYPE_LANDLOCK to BPF_PROG_TYPE_LANDLOCK_RULE
* rename Landlock version to ABI to better reflect its purpose
* use const variable (suggested by Kees Cook)
* remove useless definitions (suggested by Kees Cook)
* add detailed explanations (suggested by Kees Cook)

Changes since v5:
* cosmetic fixes
* rebase

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
---
samples/bpf/.gitignore | 1 +
samples/bpf/Makefile | 3 +
samples/bpf/bpf_load.c | 76 ++++++++++++++++-
samples/bpf/bpf_load.h | 7 ++
samples/bpf/landlock1.h | 8 ++
samples/bpf/landlock1_kern.c | 104 +++++++++++++++++++++++
samples/bpf/landlock1_user.c | 157 +++++++++++++++++++++++++++++++++++
7 files changed, 352 insertions(+), 4 deletions(-)
create mode 100644 samples/bpf/landlock1.h
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
index 74d31fd3c99c..a4c9c806f739 100644
--- a/samples/bpf/.gitignore
+++ b/samples/bpf/.gitignore
@@ -2,6 +2,7 @@ cpustat
fds_example
hbm
ibumad
+landlock1
lathist
lwt_len_hist
map_perf_test
diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 0917f8cf4fab..da246eaa8bf8 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -53,6 +53,7 @@ hostprogs-y += task_fd_query
hostprogs-y += xdp_sample_pkts
hostprogs-y += ibumad
hostprogs-y += hbm
+hostprogs-y += landlock1

# Libbpf dependencies
LIBBPF = $(TOOLS_PATH)/lib/bpf/libbpf.a
@@ -109,6 +110,7 @@ task_fd_query-objs := bpf_load.o task_fd_query_user.o $(TRACE_HELPERS)
xdp_sample_pkts-objs := xdp_sample_pkts_user.o $(TRACE_HELPERS)
ibumad-objs := bpf_load.o ibumad_user.o $(TRACE_HELPERS)
hbm-objs := bpf_load.o hbm.o $(CGROUP_HELPERS)
+landlock1-objs := bpf_load.o landlock1_user.o

# Tell kbuild to always build the programs
always := $(hostprogs-y)
@@ -168,6 +170,7 @@ always += task_fd_query_kern.o
always += xdp_sample_pkts_kern.o
always += ibumad_kern.o
always += hbm_out_kern.o
+always += landlock1_kern.o

KBUILD_HOSTCFLAGS += -I$(objtree)/usr/include
KBUILD_HOSTCFLAGS += -I$(srctree)/tools/lib/bpf/
diff --git a/samples/bpf/bpf_load.c b/samples/bpf/bpf_load.c
index 4574b1939e49..bf62d965f606 100644
--- a/samples/bpf/bpf_load.c
+++ b/samples/bpf/bpf_load.c
@@ -12,6 +12,7 @@
#include <stdlib.h>
#include <linux/bpf.h>
#include <linux/filter.h>
+#include <linux/landlock.h>
#include <linux/perf_event.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
@@ -42,6 +43,9 @@ int prog_array_fd = -1;
struct bpf_map_data map_data[MAX_MAPS];
int map_data_count;

+struct bpf_subtype_data subtype_data[MAX_PROGS];
+int subtype_data_count;
+
static int populate_prog_array(const char *event, int prog_fd)
{
int ind = atoi(event), err;
@@ -87,11 +91,15 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
bool is_sockops = strncmp(event, "sockops", 7) == 0;
bool is_sk_skb = strncmp(event, "sk_skb", 6) == 0;
bool is_sk_msg = strncmp(event, "sk_msg", 6) == 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];
int fd, efd, err, id;
struct perf_event_attr attr = {};
+ union bpf_prog_subtype *st = NULL;
+ struct bpf_subtype_data *sd = NULL;
+ struct bpf_load_program_attr load_attr;

attr.type = PERF_TYPE_TRACEPOINT;
attr.sample_type = PERF_SAMPLE_RAW;
@@ -120,6 +128,32 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
prog_type = BPF_PROG_TYPE_SK_SKB;
} else if (is_sk_msg) {
prog_type = BPF_PROG_TYPE_SK_MSG;
+ } else if (is_landlock) {
+ int i, prog_id;
+ const char *event_id = (event + 8);
+
+ if (!isdigit(*event_id)) {
+ printf("invalid prog number\n");
+ return -1;
+ }
+ prog_id = atoi(event_id);
+ for (i = 0; i < subtype_data_count; i++) {
+ if (subtype_data[i].name && strcmp(event,
+ subtype_data[i].name) == 0) {
+ /* save the prog_id for a next program */
+ sd = &subtype_data[i];
+ sd->prog_id = prog_id;
+ st = &sd->subtype;
+ free(sd->name);
+ sd->name = NULL;
+ break;
+ }
+ }
+ if (!st) {
+ printf("missing subtype\n");
+ return -1;
+ }
+ prog_type = BPF_PROG_TYPE_LANDLOCK_HOOK;
} else {
printf("Unknown event '%s'\n", event);
return -1;
@@ -128,16 +162,25 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
if (prog_cnt == MAX_PROGS)
return -1;

- fd = bpf_load_program(prog_type, prog, insns_cnt, license, kern_version,
- bpf_log_buf, BPF_LOG_BUF_SIZE);
+ memset(&load_attr, 0, sizeof(struct bpf_load_program_attr));
+ load_attr.prog_type = prog_type;
+ load_attr.prog_subtype = st;
+ load_attr.insns = prog;
+ load_attr.insns_cnt = insns_cnt;
+ load_attr.license = license;
+ load_attr.kern_version = kern_version;
+ fd = bpf_load_program_xattr(&load_attr, bpf_log_buf, BPF_LOG_BUF_SIZE);
if (fd < 0) {
printf("bpf_load_program() err=%d\n%s", errno, bpf_log_buf);
return -1;
}
+ if (sd)
+ sd->prog_fd = fd;

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 || is_sockops || is_sk_skb || is_sk_msg) {
@@ -519,6 +562,7 @@ static int do_load_bpf_file(const char *path, fixup_map_cb fixup_map)
kern_version = 0;
memset(license, 0, sizeof(license));
memset(processed_sec, 0, sizeof(processed_sec));
+ subtype_data_count = 0;

if (elf_version(EV_CURRENT) == EV_NONE)
return 1;
@@ -567,6 +611,29 @@ static int do_load_bpf_file(const char *path, fixup_map_cb fixup_map)
data_maps = data;
for (j = 0; j < MAX_MAPS; j++)
map_data[j].fd = -1;
+ } else if (strncmp(shname, "subtype", 7) == 0) {
+ processed_sec[i] = true;
+ if (*(shname + 7) != '/') {
+ printf("invalid name of subtype section");
+ return 1;
+ }
+ if (data->d_size != sizeof(union bpf_prog_subtype)) {
+ printf("invalid size of subtype section: %zd\n",
+ data->d_size);
+ printf("ref: %zd\n",
+ sizeof(union bpf_prog_subtype));
+ return 1;
+ }
+ if (subtype_data_count >= MAX_PROGS) {
+ printf("too many subtype sections");
+ return 1;
+ }
+ memcpy(&subtype_data[subtype_data_count].subtype,
+ data->d_buf,
+ sizeof(union bpf_prog_subtype));
+ subtype_data[subtype_data_count].name =
+ strdup((shname + 8));
+ subtype_data_count++;
} else if (shdr.sh_type == SHT_SYMTAB) {
strtabidx = shdr.sh_link;
symbols = data;
@@ -643,7 +710,8 @@ static int do_load_bpf_file(const char *path, fixup_map_cb fixup_map)
memcmp(shname, "cgroup/", 7) == 0 ||
memcmp(shname, "sockops", 7) == 0 ||
memcmp(shname, "sk_skb", 6) == 0 ||
- memcmp(shname, "sk_msg", 6) == 0) {
+ memcmp(shname, "sk_msg", 6) == 0 ||
+ memcmp(shname, "landlock", 8) == 0) {
ret = load_and_attach(shname, data->d_buf,
data->d_size);
if (ret != 0)
diff --git a/samples/bpf/bpf_load.h b/samples/bpf/bpf_load.h
index 814894a12974..e210b5fdf8ee 100644
--- a/samples/bpf/bpf_load.h
+++ b/samples/bpf/bpf_load.h
@@ -24,6 +24,13 @@ struct bpf_map_data {
struct bpf_load_map_def def;
};

+struct bpf_subtype_data {
+ char *name;
+ int prog_id;
+ int prog_fd;
+ union bpf_prog_subtype subtype;
+};
+
typedef void (*fixup_map_cb)(struct bpf_map_data *map, int idx);

extern int prog_fd[MAX_PROGS];
diff --git a/samples/bpf/landlock1.h b/samples/bpf/landlock1.h
new file mode 100644
index 000000000000..53b0a9447855
--- /dev/null
+++ b/samples/bpf/landlock1.h
@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Landlock sample 1 - common header
+ *
+ * Copyright © 2018-2019 Mickaël Salaün <mic@digikod.net>
+ */
+
+#define MAP_FLAG_DENY (1ULL << 0)
diff --git a/samples/bpf/landlock1_kern.c b/samples/bpf/landlock1_kern.c
new file mode 100644
index 000000000000..0298d98dd06a
--- /dev/null
+++ b/samples/bpf/landlock1_kern.c
@@ -0,0 +1,104 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Landlock sample 1 - whitelist of read only or read-write file hierarchy
+ *
+ * Copyright © 2017-2019 Mickaël Salaün <mic@digikod.net>
+ */
+
+/*
+ * This file contains a function that will be compiled to eBPF bytecode thanks
+ * to LLVM/Clang.
+ *
+ * Each SEC() means that the following function or variable will be part of a
+ * custom ELF section. This sections are then processed by the userspace part
+ * (see landlock1_user.c) to extract eBPF bytecode and take into account
+ * variables describing the eBPF program subtype or its license.
+ */
+
+#include <uapi/linux/bpf.h>
+#include <uapi/linux/landlock.h>
+
+#include "bpf_helpers.h"
+#include "landlock1.h" /* MAP_FLAG_DENY */
+
+#define MAP_MAX_ENTRIES 20
+
+SEC("maps")
+struct bpf_map_def inode_map = {
+ .type = BPF_MAP_TYPE_INODE,
+ .key_size = sizeof(u32),
+ .value_size = sizeof(u64),
+ .max_entries = MAP_MAX_ENTRIES,
+};
+
+static __always_inline __u64 get_access(void *inode)
+{
+ if (bpf_inode_map_lookup(&inode_map, inode) & MAP_FLAG_DENY)
+ return LANDLOCK_RET_DENY;
+ return LANDLOCK_RET_ALLOW;
+}
+
+SEC("subtype/landlock1")
+static union bpf_prog_subtype _subtype1 = {
+ .landlock_hook = {
+ .type = LANDLOCK_HOOK_FS_WALK,
+ }
+};
+
+/*
+ * The function fs_walk() is a simple Landlock program enforced on a set of
+ * processes. This program will be run for each walk through a file path.
+ *
+ * The argument ctx contains the context of the program when it is run, which
+ * enable to evaluate the file path. This context can change for each run of
+ * the program.
+ */
+SEC("landlock1")
+int fs_walk(struct landlock_ctx_fs_walk *ctx)
+{
+ return get_access((void *)ctx->inode);
+}
+
+SEC("subtype/landlock2")
+static union bpf_prog_subtype _subtype2 = {
+ .landlock_hook = {
+ .type = LANDLOCK_HOOK_FS_PICK,
+ /*
+ * allowed:
+ * - LANDLOCK_TRIGGER_FS_PICK_LINK
+ * - LANDLOCK_TRIGGER_FS_PICK_LINKTO
+ * - LANDLOCK_TRIGGER_FS_PICK_RECEIVE
+ * - LANDLOCK_TRIGGER_FS_PICK_MOUNTON
+ */
+ .triggers =
+ LANDLOCK_TRIGGER_FS_PICK_APPEND |
+ LANDLOCK_TRIGGER_FS_PICK_CHDIR |
+ LANDLOCK_TRIGGER_FS_PICK_CHROOT |
+ LANDLOCK_TRIGGER_FS_PICK_CREATE |
+ LANDLOCK_TRIGGER_FS_PICK_EXECUTE |
+ LANDLOCK_TRIGGER_FS_PICK_FCNTL |
+ LANDLOCK_TRIGGER_FS_PICK_GETATTR |
+ LANDLOCK_TRIGGER_FS_PICK_IOCTL |
+ LANDLOCK_TRIGGER_FS_PICK_LOCK |
+ LANDLOCK_TRIGGER_FS_PICK_MAP |
+ LANDLOCK_TRIGGER_FS_PICK_OPEN |
+ LANDLOCK_TRIGGER_FS_PICK_READ |
+ LANDLOCK_TRIGGER_FS_PICK_READDIR |
+ LANDLOCK_TRIGGER_FS_PICK_RENAME |
+ LANDLOCK_TRIGGER_FS_PICK_RENAMETO |
+ LANDLOCK_TRIGGER_FS_PICK_RMDIR |
+ LANDLOCK_TRIGGER_FS_PICK_SETATTR |
+ LANDLOCK_TRIGGER_FS_PICK_TRANSFER |
+ LANDLOCK_TRIGGER_FS_PICK_UNLINK |
+ LANDLOCK_TRIGGER_FS_PICK_WRITE,
+ }
+};
+
+SEC("landlock2")
+int fs_pick_ro(struct landlock_ctx_fs_pick *ctx)
+{
+ return get_access((void *)ctx->inode);
+}
+
+SEC("license")
+static const char _license[] = "GPL";
diff --git a/samples/bpf/landlock1_user.c b/samples/bpf/landlock1_user.c
new file mode 100644
index 000000000000..aa45932d36a8
--- /dev/null
+++ b/samples/bpf/landlock1_user.c
@@ -0,0 +1,157 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Landlock sample 1 - deny access to a set of directories (blacklisting)
+ *
+ * Copyright © 2017-2019 Mickaël Salaün <mic@digikod.net>
+ */
+
+#include "bpf/libbpf.h"
+#include "bpf_load.h"
+#include "landlock1.h" /* MAP_FLAG_DENY */
+
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h> /* open() */
+#include <linux/bpf.h>
+#include <linux/filter.h>
+#include <linux/landlock.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
+
+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_PREPEND_LANDLOCK_PROG, 0, &prog_fd)) {
+ perror("seccomp(set_hook)");
+ ret = 1;
+ }
+ close(prog_fd);
+
+ return ret;
+}
+
+#define ENV_FS_PATH_DENY_NAME "LL_PATH_DENY"
+#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;
+}
+
+static int populate_map(const char *env_var, unsigned long long value,
+ int map_fd)
+{
+ int path_nb, ref_fd, i;
+ char *env_path_name;
+ const char **path_list = NULL;
+
+ env_path_name = getenv(env_var);
+ if (!env_path_name)
+ return 0;
+ env_path_name = strdup(env_path_name);
+ path_nb = parse_path(env_path_name, &path_list);
+
+ for (i = 0; i < path_nb; i++) {
+ ref_fd = open(path_list[i], O_RDONLY | O_CLOEXEC);
+ if (ref_fd < 0) {
+ fprintf(stderr, "Failed to open \"%s\": %s\n",
+ path_list[i],
+ strerror(errno));
+ return 1;
+ }
+ if (bpf_map_update_elem(map_fd, &ref_fd, &value, BPF_ANY)) {
+ fprintf(stderr, "Failed to update the map with"
+ " \"%s\": %s\n", path_list[i],
+ strerror(errno));
+ return 1;
+ }
+ close(ref_fd);
+ }
+ free(env_path_name);
+ return 0;
+}
+
+int main(int argc, char * const argv[], char * const *envp)
+{
+ char filename[256];
+ char *cmd_path;
+ char * const *cmd_argv;
+ int ll_prog_walk, ll_prog_pick;
+
+ if (argc < 2) {
+ fprintf(stderr, "usage: %s <cmd> [args]...\n\n", argv[0]);
+ fprintf(stderr, "Launch a command in a restricted environment.\n\n");
+ fprintf(stderr, "Environment variables containing paths, each separated by a colon:\n");
+ fprintf(stderr, "* %s: list of files and directories which are denied\n",
+ ENV_FS_PATH_DENY_NAME);
+ fprintf(stderr, "\nexample:\n"
+ "%s=\"${HOME}/.ssh:${HOME}/Images\" "
+ "%s /bin/sh -i\n",
+ ENV_FS_PATH_DENY_NAME, argv[0]);
+ return 1;
+ }
+
+ snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+ if (load_bpf_file(filename)) {
+ printf("%s", bpf_log_buf);
+ return 1;
+ }
+ ll_prog_walk = prog_fd[0]; /* fs_walk */
+ ll_prog_pick = prog_fd[1]; /* fs_pick */
+ if (!ll_prog_walk || !ll_prog_pick) {
+ if (errno)
+ printf("load_bpf_file: %s\n", strerror(errno));
+ else
+ printf("load_bpf_file: Error\n");
+ return 1;
+ }
+
+ if (populate_map(ENV_FS_PATH_DENY_NAME, MAP_FLAG_DENY, map_fd[0]))
+ return 1;
+ close(map_fd[0]);
+
+ fprintf(stderr, "Launching a new sandboxed process\n");
+ if (apply_sandbox(ll_prog_walk))
+ return 1;
+ if (apply_sandbox(ll_prog_pick))
+ return 1;
+ cmd_path = argv[1];
+ cmd_argv = argv + 1;
+ execve(cmd_path, cmd_argv, envp);
+ perror("Failed to call execve");
+ return 1;
+}
--
2.20.1
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