linux/samples/seccomp/dropper.c
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   1/*
   2 * Naive system call dropper built on seccomp_filter.
   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_SET_SECCOMP, 2, ...).
  10 *
  11 * When run, returns the specified errno for the specified
  12 * system call number against the given architecture.
  13 *
  14 * Run this one as root as PR_SET_NO_NEW_PRIVS is not called.
  15 */
  16
  17#include <errno.h>
  18#include <linux/audit.h>
  19#include <linux/filter.h>
  20#include <linux/seccomp.h>
  21#include <linux/unistd.h>
  22#include <stdio.h>
  23#include <stddef.h>
  24#include <stdlib.h>
  25#include <sys/prctl.h>
  26#include <unistd.h>
  27
  28static int install_filter(int nr, int arch, int error)
  29{
  30        struct sock_filter filter[] = {
  31                BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
  32                         (offsetof(struct seccomp_data, arch))),
  33                BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, arch, 0, 3),
  34                BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
  35                         (offsetof(struct seccomp_data, nr))),
  36                BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, nr, 0, 1),
  37                BPF_STMT(BPF_RET+BPF_K,
  38                         SECCOMP_RET_ERRNO|(error & SECCOMP_RET_DATA)),
  39                BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
  40        };
  41        struct sock_fprog prog = {
  42                .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
  43                .filter = filter,
  44        };
  45        if (prctl(PR_SET_SECCOMP, 2, &prog)) {
  46                perror("prctl");
  47                return 1;
  48        }
  49        return 0;
  50}
  51
  52int main(int argc, char **argv)
  53{
  54        if (argc < 5) {
  55                fprintf(stderr, "Usage:\n"
  56                        "dropper <syscall_nr> <arch> <errno> <prog> [<args>]\n"
  57                        "Hint:  AUDIT_ARCH_I386: 0x%X\n"
  58                        "       AUDIT_ARCH_X86_64: 0x%X\n"
  59                        "\n", AUDIT_ARCH_I386, AUDIT_ARCH_X86_64);
  60                return 1;
  61        }
  62        if (install_filter(strtol(argv[1], NULL, 0), strtol(argv[2], NULL, 0),
  63                           strtol(argv[3], NULL, 0)))
  64                return 1;
  65        execv(argv[4], &argv[4]);
  66        printf("Failed to execv\n");
  67        return 255;
  68}
  69
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