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  */
  15
  16 #include <errno.h>
  17 #include <linux/audit.h>
  18 #include <linux/filter.h>
  19 #include <linux/seccomp.h>
  20 #include <linux/unistd.h>
  21 #include <stdio.h>
  22 #include <stddef.h>
  23 #include <stdlib.h>
  24 #include <sys/prctl.h>
  25 #include <unistd.h>
  26
  27 static int install_filter(int nr, int arch, int error)
  28 {
  29         struct sock_filter filter[] = {
  30                 BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
  31                          (offsetof(struct seccomp_data, arch))),
  32                 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, arch, 0, 3),
  33                 BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
  34                          (offsetof(struct seccomp_data, nr))),
  35                 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, nr, 0, 1),
  36                 BPF_STMT(BPF_RET+BPF_K,
  37                          SECCOMP_RET_ERRNO|(error & SECCOMP_RET_DATA)),
  38                 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
  39         };
  40         struct sock_fprog prog = {
  41                 .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
  42                 .filter = filter,
  43         };
  44         if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
  45                 perror("prctl(NO_NEW_PRIVS)");
  46                 return 1;
  47         }
  48         if (prctl(PR_SET_SECCOMP, 2, &prog)) {
  49                 perror("prctl(PR_SET_SECCOMP)");
  50                 return 1;
  51         }
  52         return 0;
  53 }
  54
  55 int main(int argc, char **argv)
  56 {
  57         if (argc < 5) {
  58                 fprintf(stderr, "Usage:\n"
  59                         "dropper <syscall_nr> <arch> <errno> <prog> [<args>]\n"
  60                         "Hint:  AUDIT_ARCH_I386: 0x%X\n"
  61                         "       AUDIT_ARCH_X86_64: 0x%X\n"
  62                         "\n", AUDIT_ARCH_I386, AUDIT_ARCH_X86_64);
  63                 return 1;
  64         }
  65         if (install_filter(strtol(argv[1], NULL, 0), strtol(argv[2], NULL, 0),
  66                            strtol(argv[3], NULL, 0)))
  67                 return 1;
  68         execv(argv[4], &argv[4]);
  69         printf("Failed to execv\n");
  70         return 255;
  71 }