samples/seccomp/bpf-fancy.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Seccomp BPF example using a macro-based generator.
   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_ATTACH_SECCOMP_FILTER).
  11  */
  12
  13 #include <linux/filter.h>
  14 #include <linux/seccomp.h>
  15 #include <linux/unistd.h>
  16 #include <stdio.h>
  17 #include <string.h>
  18 #include <sys/prctl.h>
  19 #include <unistd.h>
  20
  21 #include "bpf-helper.h"
  22
  23 #ifndef PR_SET_NO_NEW_PRIVS
  24 #define PR_SET_NO_NEW_PRIVS 38
  25 #endif
  26
  27 int main(int argc, char **argv)
  28 {
  29         struct bpf_labels l = {
  30                 .count = 0,
  31         };
  32         static const char msg1[] = "Please type something: ";
  33         static const char msg2[] = "You typed: ";
  34         char buf[256];
  35         struct sock_filter filter[] = {
  36                 /* TODO: LOAD_SYSCALL_NR(arch) and enforce an arch */
  37                 LOAD_SYSCALL_NR,
  38                 SYSCALL(__NR_exit, ALLOW),
  39                 SYSCALL(__NR_exit_group, ALLOW),
  40                 SYSCALL(__NR_write, JUMP(&l, write_fd)),
  41                 SYSCALL(__NR_read, JUMP(&l, read)),
  42                 DENY,  /* Don't passthrough into a label */
  43
  44                 LABEL(&l, read),
  45                 ARG(0),
  46                 JNE(STDIN_FILENO, DENY),
  47                 ARG(1),
  48                 JNE((unsigned long)buf, DENY),
  49                 ARG(2),
  50                 JGE(sizeof(buf), DENY),
  51                 ALLOW,
  52
  53                 LABEL(&l, write_fd),
  54                 ARG(0),
  55                 JEQ(STDOUT_FILENO, JUMP(&l, write_buf)),
  56                 JEQ(STDERR_FILENO, JUMP(&l, write_buf)),
  57                 DENY,
  58
  59                 LABEL(&l, write_buf),
  60                 ARG(1),
  61                 JEQ((unsigned long)msg1, JUMP(&l, msg1_len)),
  62                 JEQ((unsigned long)msg2, JUMP(&l, msg2_len)),
  63                 JEQ((unsigned long)buf, JUMP(&l, buf_len)),
  64                 DENY,
  65
  66                 LABEL(&l, msg1_len),
  67                 ARG(2),
  68                 JLT(sizeof(msg1), ALLOW),
  69                 DENY,
  70
  71                 LABEL(&l, msg2_len),
  72                 ARG(2),
  73                 JLT(sizeof(msg2), ALLOW),
  74                 DENY,
  75
  76                 LABEL(&l, buf_len),
  77                 ARG(2),
  78                 JLT(sizeof(buf), ALLOW),
  79                 DENY,
  80         };
  81         struct sock_fprog prog = {
  82                 .filter = filter,
  83                 .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
  84         };
  85         ssize_t bytes;
  86         bpf_resolve_jumps(&l, filter, sizeof(filter)/sizeof(*filter));
  87
  88         if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
  89                 perror("prctl(NO_NEW_PRIVS)");
  90                 return 1;
  91         }
  92
  93         if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) {
  94                 perror("prctl(SECCOMP)");
  95                 return 1;
  96         }
  97         syscall(__NR_write, STDOUT_FILENO, msg1, strlen(msg1));
  98         bytes = syscall(__NR_read, STDIN_FILENO, buf, sizeof(buf)-1);
  99         bytes = (bytes > 0 ? bytes : 0);
 100         syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2));
 101         syscall(__NR_write, STDERR_FILENO, buf, bytes);
 102         /* Now get killed */
 103         syscall(__NR_write, STDERR_FILENO, msg2, strlen(msg2)+2);
 104         return 0;
 105 }