linux/samples/seccomp/bpf-fancy.c
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   1/*
   2 * Seccomp BPF example using a macro-based generator.
   3 *
   4 * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
   5 * Author: Will Drewry <wad@chromium.org>
   6 *
   7 * The code may be used by anyone for any purpose,
   8 * and can serve as a starting point for developing
   9 * applications using prctl(PR_ATTACH_SECCOMP_FILTER).
  10 */
  11
  12#include <linux/filter.h>
  13#include <linux/seccomp.h>
  14#include <linux/unistd.h>
  15#include <stdio.h>
  16#include <string.h>
  17#include <sys/prctl.h>
  18#include <unistd.h>
  19
  20#include "bpf-helper.h"
  21
  22#ifndef PR_SET_NO_NEW_PRIVS
  23#define PR_SET_NO_NEW_PRIVS 38
  24#endif
  25
  26int main(int argc, char **argv)
  27{
  28        struct bpf_labels l;
  29        static const char msg1[] = "Please type something: ";
  30        static const char msg2[] = "You typed: ";
  31        char buf[256];
  32        struct sock_filter filter[] = {
  33                /* TODO: LOAD_SYSCALL_NR(arch) and enforce an arch */
  34                LOAD_SYSCALL_NR,
  35                SYSCALL(__NR_exit, ALLOW),
  36                SYSCALL(__NR_exit_group, ALLOW),
  37                SYSCALL(__NR_write, JUMP(&l, write_fd)),
  38                SYSCALL(__NR_read, JUMP(&l, read)),
  39                DENY,  /* Don't passthrough into a label */
  40
  41                LABEL(&l, read),
  42                ARG(0),
  43                JNE(STDIN_FILENO, DENY),
  44                ARG(1),
  45                JNE((unsigned long)buf, DENY),
  46                ARG(2),
  47                JGE(sizeof(buf), DENY),
  48                ALLOW,
  49
  50                LABEL(&l, write_fd),
  51                ARG(0),
  52                JEQ(STDOUT_FILENO, JUMP(&l, write_buf)),
  53                JEQ(STDERR_FILENO, JUMP(&l, write_buf)),
  54                DENY,
  55
  56                LABEL(&l, write_buf),
  57                ARG(1),
  58                JEQ((unsigned long)msg1, JUMP(&l, msg1_len)),
  59                JEQ((unsigned long)msg2, JUMP(&l, msg2_len)),
  60                JEQ((unsigned long)buf, JUMP(&l, buf_len)),
  61                DENY,
  62
  63                LABEL(&l, msg1_len),
  64                ARG(2),
  65                JLT(sizeof(msg1), ALLOW),
  66                DENY,
  67
  68                LABEL(&l, msg2_len),
  69                ARG(2),
  70                JLT(sizeof(msg2), ALLOW),
  71                DENY,
  72
  73                LABEL(&l, buf_len),
  74                ARG(2),
  75                JLT(sizeof(buf), ALLOW),
  76                DENY,
  77        };
  78        struct sock_fprog prog = {
  79                .filter = filter,
  80                .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
  81        };
  82        ssize_t bytes;
  83        bpf_resolve_jumps(&l, filter, sizeof(filter)/sizeof(*filter));
  84
  85        if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
  86                perror("prctl(NO_NEW_PRIVS)");
  87                return 1;
  88        }
  89
  90        if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) {
  91                perror("prctl(SECCOMP)");
  92                return 1;
  93        }
  94        syscall(__NR_write, STDOUT_FILENO, msg1, strlen(msg1));
  95        bytes = syscall(__NR_read, STDIN_FILENO, buf, sizeof(buf)-1);
  96        bytes = (bytes > 0 ? bytes : 0);
  97        syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2));
  98        syscall(__NR_write, STDERR_FILENO, buf, bytes);
  99        /* Now get killed */
 100        syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2)+2);
 101        return 0;
 102}
 103
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