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/*
* parse and setup OCI seccomp filter
* Copyright (c) 2020 Daniel Golle <daniel@makrotopia.org>
* seccomp example with syscall reporting
* Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
* Authors:
* Kees Cook <keescook@chromium.org>
* Will Drewry <wad@chromium.org>
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#define _GNU_SOURCE 1
#include <stddef.h>
#include <stdlib.h>
#include <unistd.h>
#include <libubox/utils.h>
#include <libubox/blobmsg.h>
#include <libubox/blobmsg_json.h>
#include "log.h"
#include "seccomp-bpf.h"
#include "seccomp-oci.h"
#include "../syscall-names.h"
#include "seccomp-syscalls-helpers.h"
static uint32_t resolve_action(char *actname)
{
if (!strcmp(actname, "SCMP_ACT_KILL"))
return SECCOMP_RET_KILL;
else if (!strcmp(actname, "SCMP_ACT_KILL_PROCESS"))
return SECCOMP_RET_KILLPROCESS;
else if (!strcmp(actname, "SCMP_ACT_TRAP"))
return SECCOMP_RET_TRAP;
else if (!strcmp(actname, "SCMP_ACT_ERRNO"))
return SECCOMP_RET_ERRNO;
else if (!strcmp(actname, "SCMP_ACT_ERROR"))
return SECCOMP_RET_ERRNO;
else if (!strcmp(actname, "SCMP_ACT_TRACE"))
return SECCOMP_RET_TRACE;
else if (!strcmp(actname, "SCMP_ACT_ALLOW"))
return SECCOMP_RET_ALLOW;
else if (!strcmp(actname, "SCMP_ACT_LOG"))
return SECCOMP_RET_LOGALLOW;
else {
ERROR("unknown seccomp action %s\n", actname);
return SECCOMP_RET_KILL;
}
}
static uint32_t resolve_architecture(char *archname)
{
if (!strcmp(archname, "SCMP_ARCH_X86"))
return AUDIT_ARCH_I386;
else if (!strcmp(archname, "SCMP_ARCH_X86_64"))
return AUDIT_ARCH_X86_64;
else if (!strcmp(archname, "SCMP_ARCH_X32"))
/*
* return AUDIT_ARCH_X86_64;
* 32-bit userland on 64-bit kernel is not supported yet
*/
return 0;
else if (!strcmp(archname, "SCMP_ARCH_ARM"))
return AUDIT_ARCH_ARM;
else if (!strcmp(archname, "SCMP_ARCH_AARCH64"))
return AUDIT_ARCH_AARCH64;
else if (!strcmp(archname, "SCMP_ARCH_MIPS"))
return AUDIT_ARCH_MIPS;
else if (!strcmp(archname, "SCMP_ARCH_MIPS64"))
return AUDIT_ARCH_MIPS64;
else if (!strcmp(archname, "SCMP_ARCH_MIPS64N32"))
return AUDIT_ARCH_MIPS64N32;
else if (!strcmp(archname, "SCMP_ARCH_MIPSEL"))
return AUDIT_ARCH_MIPSEL;
else if (!strcmp(archname, "SCMP_ARCH_MIPSEL64"))
return AUDIT_ARCH_MIPSEL64;
else if (!strcmp(archname, "SCMP_ARCH_MIPSEL64N32"))
return AUDIT_ARCH_MIPSEL64N32;
else if (!strcmp(archname, "SCMP_ARCH_PPC"))
return AUDIT_ARCH_PPC;
else if (!strcmp(archname, "SCMP_ARCH_PPC64"))
return AUDIT_ARCH_PPC64;
else if (!strcmp(archname, "SCMP_ARCH_PPC64LE"))
return AUDIT_ARCH_PPC64LE;
else if (!strcmp(archname, "SCMP_ARCH_S390"))
return AUDIT_ARCH_S390;
else if (!strcmp(archname, "SCMP_ARCH_S390X"))
return AUDIT_ARCH_S390X;
else if (!strcmp(archname, "SCMP_ARCH_PARISC"))
return AUDIT_ARCH_PARISC;
else if (!strcmp(archname, "SCMP_ARCH_PARISC64"))
return AUDIT_ARCH_PARISC64;
else {
ERROR("unknown seccomp architecture %s\n", archname);
return 0;
}
}
enum {
OCI_LINUX_SECCOMP_DEFAULTACTION,
OCI_LINUX_SECCOMP_ARCHITECTURES,
OCI_LINUX_SECCOMP_FLAGS,
OCI_LINUX_SECCOMP_SYSCALLS,
__OCI_LINUX_SECCOMP_MAX,
};
static const struct blobmsg_policy oci_linux_seccomp_policy[] = {
[OCI_LINUX_SECCOMP_DEFAULTACTION] = { "defaultAction", BLOBMSG_TYPE_STRING },
[OCI_LINUX_SECCOMP_ARCHITECTURES] = { "architectures", BLOBMSG_TYPE_ARRAY },
[OCI_LINUX_SECCOMP_FLAGS] = { "flags", BLOBMSG_TYPE_ARRAY },
[OCI_LINUX_SECCOMP_SYSCALLS] = { "syscalls", BLOBMSG_TYPE_ARRAY },
};
enum {
OCI_LINUX_SECCOMP_SYSCALLS_NAMES,
OCI_LINUX_SECCOMP_SYSCALLS_ACTION,
OCI_LINUX_SECCOMP_SYSCALLS_ERRNORET,
OCI_LINUX_SECCOMP_SYSCALLS_ARGS,
__OCI_LINUX_SECCOMP_SYSCALLS_MAX
};
static const struct blobmsg_policy oci_linux_seccomp_syscalls_policy[] = {
[OCI_LINUX_SECCOMP_SYSCALLS_NAMES] = { "names", BLOBMSG_TYPE_ARRAY },
[OCI_LINUX_SECCOMP_SYSCALLS_ERRNORET] = { "errnoRet", BLOBMSG_TYPE_INT32 },
[OCI_LINUX_SECCOMP_SYSCALLS_ARGS] = { "args", BLOBMSG_TYPE_ARRAY },
[OCI_LINUX_SECCOMP_SYSCALLS_ACTION] = { "action", BLOBMSG_TYPE_STRING },
};
enum {
OCI_LINUX_SECCOMP_SYSCALLS_ARGS_INDEX,
OCI_LINUX_SECCOMP_SYSCALLS_ARGS_VALUE,
OCI_LINUX_SECCOMP_SYSCALLS_ARGS_VALUETWO,
OCI_LINUX_SECCOMP_SYSCALLS_ARGS_OP,
__OCI_LINUX_SECCOMP_SYSCALLS_ARGS_MAX
};
static const struct blobmsg_policy oci_linux_seccomp_syscalls_args_policy[] = {
[OCI_LINUX_SECCOMP_SYSCALLS_ARGS_INDEX] = { "index", BLOBMSG_TYPE_INT32 },
[OCI_LINUX_SECCOMP_SYSCALLS_ARGS_VALUE] = { "value", BLOBMSG_TYPE_INT64 },
[OCI_LINUX_SECCOMP_SYSCALLS_ARGS_VALUETWO] = { "valueTwo", BLOBMSG_TYPE_INT64 },
[OCI_LINUX_SECCOMP_SYSCALLS_ARGS_OP] = { "op", BLOBMSG_TYPE_STRING },
};
struct sock_fprog *parseOCIlinuxseccomp(struct blob_attr *msg)
{
struct blob_attr *tb[__OCI_LINUX_SECCOMP_MAX];
struct blob_attr *tbn[__OCI_LINUX_SECCOMP_SYSCALLS_MAX];
struct blob_attr *tba[__OCI_LINUX_SECCOMP_SYSCALLS_ARGS_MAX];
struct blob_attr *cur, *curn, *curarg;
int rem, remn, remargs, sc;
struct sock_filter *filter;
struct sock_fprog *prog;
int sz = 5, idx = 0;
uint32_t default_policy = 0;
uint32_t seccomp_arch;
blobmsg_parse(oci_linux_seccomp_policy, __OCI_LINUX_SECCOMP_MAX, tb, blobmsg_data(msg), blobmsg_len(msg));
if (!tb[OCI_LINUX_SECCOMP_DEFAULTACTION]) {
ERROR("seccomp: no default action set\n");
return NULL;
}
default_policy = resolve_action(blobmsg_get_string(tb[OCI_LINUX_SECCOMP_DEFAULTACTION]));
/* verify architecture while ignoring the x86_64 anomaly for now */
blobmsg_for_each_attr(cur, tb[OCI_LINUX_SECCOMP_ARCHITECTURES], rem) {
seccomp_arch = resolve_architecture(blobmsg_get_string(cur));
/* take the first useful arch for now */
if (seccomp_arch)
break;
}
if (ARCH_NR != seccomp_arch) {
ERROR("seccomp architecture doesn't match system\n");
return NULL;
}
blobmsg_for_each_attr(cur, tb[OCI_LINUX_SECCOMP_SYSCALLS], rem) {
blobmsg_parse(oci_linux_seccomp_syscalls_policy, __OCI_LINUX_SECCOMP_SYSCALLS_MAX, tbn, blobmsg_data(cur), blobmsg_len(cur));
blobmsg_for_each_attr(curn, tbn[OCI_LINUX_SECCOMP_SYSCALLS_NAMES], remn)
sz += 2;
if (tbn[OCI_LINUX_SECCOMP_SYSCALLS_ARGS])
blobmsg_for_each_attr(curarg, tbn[OCI_LINUX_SECCOMP_SYSCALLS_ARGS], remargs)
sz++;
}
prog = malloc(sizeof(struct sock_fprog));
if (!prog)
return NULL;
filter = calloc(sz, sizeof(struct sock_filter));
if (!filter) {
ERROR("failed to allocate memory for seccomp filter\n");
goto errout2;
}
/* validate arch */
set_filter(&filter[idx++], BPF_LD + BPF_W + BPF_ABS, 0, 0, arch_nr);
set_filter(&filter[idx++], BPF_JMP + BPF_JEQ + BPF_K, 1, 0, ARCH_NR);
set_filter(&filter[idx++], BPF_RET + BPF_K, 0, 0, SECCOMP_RET_KILL);
/* get syscall */
set_filter(&filter[idx++], BPF_LD + BPF_W + BPF_ABS, 0, 0, syscall_nr);
blobmsg_for_each_attr(cur, tb[OCI_LINUX_SECCOMP_SYSCALLS], rem) {
uint32_t action;
blobmsg_parse(oci_linux_seccomp_syscalls_policy, __OCI_LINUX_SECCOMP_SYSCALLS_MAX, tbn, blobmsg_data(cur), blobmsg_len(cur));
action = resolve_action(blobmsg_get_string(tbn[OCI_LINUX_SECCOMP_SYSCALLS_ACTION]));
if (tbn[OCI_LINUX_SECCOMP_SYSCALLS_ERRNORET]) {
if (action != SECCOMP_RET_ERRNO)
goto errout1;
action = SECCOMP_RET_ERROR(blobmsg_get_u32(tbn[OCI_LINUX_SECCOMP_SYSCALLS_ERRNORET]));
} else if (action == SECCOMP_RET_ERRNO)
action = SECCOMP_RET_ERROR(EPERM);
blobmsg_for_each_attr(curn, tbn[OCI_LINUX_SECCOMP_SYSCALLS_NAMES], remn) {
sc = find_syscall(blobmsg_get_string(curn));
if (sc == -1) {
ERROR("unknown syscall '%s'\n", blobmsg_get_string(curn));
goto errout1;
}
/* add rule to filter */
set_filter(&filter[idx++], BPF_JMP + BPF_JEQ + BPF_K, 0, 1, sc);
set_filter(&filter[idx++], BPF_RET + BPF_K, 0, 0, action);
}
blobmsg_for_each_attr(curn, tbn[OCI_LINUX_SECCOMP_SYSCALLS_ARGS], remn) {
blobmsg_parse(oci_linux_seccomp_syscalls_args_policy, __OCI_LINUX_SECCOMP_SYSCALLS_ARGS_MAX, tba, blobmsg_data(curn), blobmsg_len(curn));
/* ToDo: process args */
}
}
set_filter(&filter[idx], BPF_RET + BPF_K, 0, 0, default_policy);
prog->len = (unsigned short) idx + 1;
prog->filter = filter;
return prog;
errout1:
free(prog->filter);
errout2:
free(prog);
return NULL;
}
int applyOCIlinuxseccomp(struct sock_fprog *prog)
{
if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
ERROR("prctl(PR_SET_NO_NEW_PRIVS) failed: %m\n");
goto errout;
}
if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, prog)) {
ERROR("prctl(PR_SET_SECCOMP) failed: %m\n");
goto errout;
}
free(prog);
return 0;
errout:
free(prog->filter);
free(prog);
return errno;
}
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