LXR linux/samples/seccomp/dropper.c

   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Naive system call dropper built on seccomp_filter.
   4 *
   5 * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
   6 * Author: Will Drewry <wad@chromium.org>
   7 *
   8 * The code may be used by anyone for any purpose,
   9 * and can serve as a starting point for developing
  10 * applications using prctl(PR_SET_SECCOMP, 2, ...).
  11 *
  12 * When run, returns the specified errno for the specified
  13 * system call number against the given architecture.
  14 *
  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_NO_NEW_PRIVS, 1, 0, 0, 0)) {
  46                perror("prctl(NO_NEW_PRIVS)");
  47                return 1;
  48        }
  49        if (prctl(PR_SET_SECCOMP, 2, &prog)) {
  50                perror("prctl(PR_SET_SECCOMP)");
  51                return 1;
  52        }
  53        return 0;
  54}
  55
  56int main(int argc, char **argv)
  57{
  58        if (argc < 5) {
  59                fprintf(stderr, "Usage:\n"
  60                        "dropper <syscall_nr> <arch> <errno> <prog> [<args>]\n"
  61                        "Hint:  AUDIT_ARCH_I386: 0x%X\n"
  62                        "       AUDIT_ARCH_X86_64: 0x%X\n"
  63                        "\n", AUDIT_ARCH_I386, AUDIT_ARCH_X86_64);
  64                return 1;
  65        }
  66        if (install_filter(strtol(argv[1], NULL, 0), strtol(argv[2], NULL, 0),
  67                           strtol(argv[3], NULL, 0)))
  68                return 1;
  69        execv(argv[4], &argv[4]);
  70        printf("Failed to execv\n");
  71        return 255;
  72}
  73