samples/seccomp/dropper.c

   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
  28 static 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
  52 int 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 }