Seccomp Tools

Potenti strumenti per l'analisi di seccomp.

Questo progetto è pensato principalmente (ma non esclusivamente) per analizzare i sandbox seccomp nelle sfide pwn dei CTF. Alcune funzionalità sono specifiche per i CTF, ma sono altrettanto utili per analizzare filtri seccomp reali.

Funzionalità

• Dump - Dump automatico del BPF seccomp dagli eseguibili.
• Disasm - Converte il BPF seccomp in un formato leggibile.
  • Con semplice decompilazione.
  • Con nomi e argomenti delle syscall quando possibile.
  • Colorato!
• Asm - Rende la scrittura di regole seccomp semplice come scrivere codice.
• Emu - Emula le regole seccomp.
• Explain - Riassume un filtro come policy per azione (quali syscall sono consentite/uccise, e quando).
• Audit - Scansiona un filtro per debolezze e vie di fuga (guard mancanti per arch/x32, syscall pericolose, ...).
• Supporto multi-architettura.

Installazione

Disponibile su RubyGems.org!``` $ gem install seccomp-tools

Se la compilazione fallisce, prova:```
sudo apt install gcc ruby-dev make

quindi installa di nuovo seccomp-tools.

Interfaccia a riga di comando

seccomp-tools```bash

$ seccomp-tools --help

Usage: seccomp-tools [--version] [--help] []

List of commands:

asm Seccomp bpf assembler.

audit Assess a seccomp filter for weaknesses and escape routes.

completion Print a shell completion script.

disasm Disassemble seccomp bpf.

dump Automatically dump seccomp bpf from executable(s).

emu Emulate seccomp rules.

explain Summarize a seccomp filter as a per-action policy.

See 'seccomp-tools --help' to read about a specific subcommand.

$ seccomp-tools dump --help

dump - Automatically dump seccomp bpf from executable(s).

NOTE: This command is only available on Linux.

Usage: seccomp-tools dump [EXEC] [options]

-c, --sh-exec Executes the given command (via sh) and dumps its seccomp.

Use this to pass arguments or pipe things to the executable.

e.g. use -c "./bin > /dev/null" to keep the program output out of the result.

Takes precedence over the positional argument.

-l, --limit LIMIT Dump only the first LIMIT installed filters.

Only meaningful when the input is an executable or --pid. Default: 1

An executable is killed once it reaches LIMIT.

-p, --pid PID Dump the seccomp filters installed on an existing process.

You must have CAP_SYS_ADMIN (e.g. be root) to use this option.

-t, --timeout SEC Timeout (seconds) for the execution. Default: no timeout

This option is ignored when --pid is given.

-f, --format FORMAT Output format. FORMAT can only be one of <disasm|raw|inspect>.

Default: disasm

-o, --output FILE Write output to FILE instead of stdout.

If multiple seccomp syscalls have been invoked (see --limit),

results are written to FILE, FILE_1, FILE_2, etc.

For example, with "--output out.bpf" the output files are out.bpf, out_1.bpf, ...

### dump

Esegue il dump del BPF seccomp da un eseguibile, utilizzando la syscall `ptrace`.

NOTA: l'eseguibile target viene effettivamente eseguito, quindi prestare attenzione con binari non attendibili.```bash
$ file spec/binary/twctf-2016-diary
# spec/binary/twctf-2016-diary: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.24, BuildID[sha1]=3648e29153ac0259a0b7c3e25537a5334f50107f, not stripped

$ seccomp-tools dump spec/binary/twctf-2016-diary
#  line  CODE  JT   JF      K
# =================================
#  0000: 0x20 0x00 0x00 0x00000000  A = sys_number
#  0001: 0x15 0x00 0x01 0x00000002  if (A != open) goto 0003
#  0002: 0x06 0x00 0x00 0x00000000  return KILL
#  0003: 0x15 0x00 0x01 0x00000101  if (A != openat) goto 0005
#  0004: 0x06 0x00 0x00 0x00000000  return KILL
#  0005: 0x15 0x00 0x01 0x0000003b  if (A != execve) goto 0007
#  0006: 0x06 0x00 0x00 0x00000000  return KILL
#  0007: 0x15 0x00 0x01 0x00000038  if (A != clone) goto 0009
#  0008: 0x06 0x00 0x00 0x00000000  return KILL
#  0009: 0x15 0x00 0x01 0x00000039  if (A != fork) goto 0011
#  0010: 0x06 0x00 0x00 0x00000000  return KILL
#  0011: 0x15 0x00 0x01 0x0000003a  if (A != vfork) goto 0013
#  0012: 0x06 0x00 0x00 0x00000000  return KILL
#  0013: 0x15 0x00 0x01 0x00000055  if (A != creat) goto 0015
#  0014: 0x06 0x00 0x00 0x00000000  return KILL
#  0015: 0x15 0x00 0x01 0x00000142  if (A != execveat) goto 0017
#  0016: 0x06 0x00 0x00 0x00000000  return KILL
#  0017: 0x06 0x00 0x00 0x7fff0000  return ALLOW

$ seccomp-tools dump spec/binary/twctf-2016-diary -f inspect
# "\x20\x00\x00\x00\x00\x00\x00\x00\x15\x00\x00\x01\x02\x00\x00\x00\x06\x00\x00\x00\x00\x00\x00\x00\x15\x00\x00\x01\x01\x01\x00\x00\x06\x00\x00\x00\x00\x00\x00\x00\x15\x00\x00\x01\x3B\x00\x00\x00\x06\x00\x00\x00\x00\x00\x00\x00\x15\x00\x00\x01\x38\x00\x00\x00\x06\x00\x00\x00\x00\x00\x00\x00\x15\x00\x00\x01\x39\x00\x00\x00\x06\x00\x00\x00\x00\x00\x00\x00\x15\x00\x00\x01\x3A\x00\x00\x00\x06\x00\x00\x00\x00\x00\x00\x00\x15\x00\x00\x01\x55\x00\x00\x00\x06\x00\x00\x00\x00\x00\x00\x00\x15\x00\x00\x01\x42\x01\x00\x00\x06\x00\x00\x00\x00\x00\x00\x00\x06\x00\x00\x00\x00\x00\xFF\x7F"

$ seccomp-tools dump spec/binary/twctf-2016-diary -f raw | xxd
# 00000000: 2000 0000 0000 0000 1500 0001 0200 0000   ...............
# 00000010: 0600 0000 0000 0000 1500 0001 0101 0000  ................
# 00000020: 0600 0000 0000 0000 1500 0001 3b00 0000  ............;...
# 00000030: 0600 0000 0000 0000 1500 0001 3800 0000  ............8...
# 00000040: 0600 0000 0000 0000 1500 0001 3900 0000  ............9...
# 00000050: 0600 0000 0000 0000 1500 0001 3a00 0000  ............:...
# 00000060: 0600 0000 0000 0000 1500 0001 5500 0000  ............U...
# 00000070: 0600 0000 0000 0000 1500 0001 4201 0000  ............B...
# 00000080: 0600 0000 0000 0000 0600 0000 0000 ff7f  ................

disasm

Disassembla il BPF seccomp grezzo in un formato leggibile.```bash $ xxd spec/data/twctf-2016-diary.bpf | head -n 3

00000000: 2000 0000 0000 0000 1500 0001 0200 0000 ...............

00000010: 0600 0000 0000 0000 1500 0001 0101 0000 ................

00000020: 0600 0000 0000 0000 1500 0001 3b00 0000 ............;...