jail/seccomp.c

   1 /*
   2  * seccomp example with syscall reporting
   3  *
   4  * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
   5  * Authors:
   6  *  Kees Cook <keescook@chromium.org>
   7  *  Will Drewry <wad@chromium.org>
   8  *
   9  * Use of this source code is governed by a BSD-style license that can be
  10  * found in the LICENSE file.
  11  */
  12 #define _GNU_SOURCE 1
  13 #include <stddef.h>
  14 #include <stdlib.h>
  15 #include <unistd.h>
  16
  17 #include <libubox/utils.h>
  18 #include <libubox/blobmsg.h>
  19 #include <libubox/blobmsg_json.h>
  20
  21 #include "seccomp-bpf.h"
  22 #include "seccomp.h"
  23 #include "../syscall-names.h"
  24
  25 static int max_syscall = ARRAY_SIZE(syscall_names);
  26
  27 static int find_syscall(const char *name)
  28 {
  29         int i;
  30
  31         for (i = 0; i < max_syscall; i++)
  32                 if (syscall_names[i] && !strcmp(syscall_names[i], name))
  33                         return i;
  34
  35         return -1;
  36 }
  37
  38 static void set_filter(struct sock_filter *filter, __u16 code, __u8 jt, __u8 jf, __u32 k)
  39 {
  40         filter->code = code;
  41         filter->jt = jt;
  42         filter->jf = jf;
  43         filter->k = k;
  44 }
  45
  46 int install_syscall_filter(const char *argv, const char *file)
  47 {
  48         enum {
  49                 SECCOMP_WHITELIST,
  50                 SECCOMP_POLICY,
  51                 __SECCOMP_MAX
  52         };
  53         static const struct blobmsg_policy policy[__SECCOMP_MAX] = {
  54                 [SECCOMP_WHITELIST] = { .name = "whitelist", .type = BLOBMSG_TYPE_ARRAY },
  55                 [SECCOMP_POLICY] = { .name = "policy", .type = BLOBMSG_TYPE_INT32 },
  56         };
  57         struct blob_buf b = { 0 };
  58         struct blob_attr *tb[__SECCOMP_MAX];
  59         struct blob_attr *cur;
  60         int rem;
  61
  62         struct sock_filter *filter;
  63         struct sock_fprog prog = { 0 };
  64         int sz = 5, idx = 0, default_policy = 0;
  65
  66         INFO("%s: setting up syscall filter\n", argv);
  67
  68         blob_buf_init(&b, 0);
  69         if (!blobmsg_add_json_from_file(&b, file)) {
  70                 INFO("%s: failed to load %s\n", argv, file);
  71                 return -1;
  72         }
  73
  74         blobmsg_parse(policy, __SECCOMP_MAX, tb, blob_data(b.head), blob_len(b.head));
  75         if (!tb[SECCOMP_WHITELIST]) {
  76                 INFO("%s: %s is missing the syscall table\n", argv, file);
  77                 return -1;
  78         }
  79
  80         if (tb[SECCOMP_POLICY])
  81                 default_policy = blobmsg_get_u32(tb[SECCOMP_POLICY]);
  82
  83         blobmsg_for_each_attr(cur, tb[SECCOMP_WHITELIST], rem)
  84                 sz += 2;
  85
  86         filter = calloc(sz, sizeof(struct sock_filter));
  87         if (!filter) {
  88                 INFO("failed to allocate filter memory\n");
  89                 return -1;
  90         }
  91
  92         /* validate arch */
  93         set_filter(&filter[idx++], BPF_LD + BPF_W + BPF_ABS, 0, 0, arch_nr);
  94         set_filter(&filter[idx++], BPF_JMP + BPF_JEQ + BPF_K, 1, 0, ARCH_NR);
  95         set_filter(&filter[idx++], BPF_RET + BPF_K, 0, 0, SECCOMP_RET_KILL);
  96
  97         /* get syscall */
  98         set_filter(&filter[idx++], BPF_LD + BPF_W + BPF_ABS, 0, 0, syscall_nr);
  99
 100         blobmsg_for_each_attr(cur, tb[SECCOMP_WHITELIST], rem) {
 101                 char *name = blobmsg_get_string(cur);
 102                 int nr;
 103
 104                 if (!name) {
 105                         INFO("%s: invalid syscall name\n", argv);
 106                         continue;
 107                 }
 108
 109                 nr  = find_syscall(name);
 110                 if (nr == -1) {
 111                         INFO("%s: unknown syscall %s\n", argv, name);
 112                         continue;
 113                 }
 114
 115                 /* add whitelist */
 116                 set_filter(&filter[idx++], BPF_JMP + BPF_JEQ + BPF_K, 0, 1, nr);
 117                 set_filter(&filter[idx++], BPF_RET + BPF_K, 0, 0, SECCOMP_RET_ALLOW);
 118         }
 119
 120         if (default_policy)
 121                 /* return -1 and set errno */
 122                 set_filter(&filter[idx], BPF_RET + BPF_K, 0, 0, SECCOMP_RET_LOGGER(default_policy));
 123         else
 124                 /* kill the process */
 125                 set_filter(&filter[idx], BPF_RET + BPF_K, 0, 0, SECCOMP_RET_KILL);
 126
 127         if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
 128                 INFO("%s: prctl(PR_SET_NO_NEW_PRIVS) failed: %s\n", argv, strerror(errno));
 129                 return errno;
 130         }
 131
 132         prog.len = (unsigned short) idx + 1;
 133         prog.filter = filter;
 134
 135         if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) {
 136                 INFO("%s: prctl(PR_SET_SECCOMP) failed: %s\n", argv, strerror(errno));
 137                 return errno;
 138         }
 139         return 0;
 140 }