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lib/ai/tools/shell/util.ex
defmodule AI.Tools.Shell.Util do
@moduledoc """
Utility functions for shell command validation and security checking.
This module provides functions to analyze shell commands for potentially
dangerous syntax that could be used for command injection or other
security vulnerabilities.
"""
@doc """
Checks if a shell command contains disallowed syntax.
Returns `true` if the command contains dangerous patterns like:
- Pipes, redirection, or logical operators
- Command substitution or process substitution
- Unbalanced quotes or shell escape sequences
- Dangerous characters like newlines, NUL bytes, or zero-width spaces
## Examples
iex> AI.Tools.Shell.Util.contains_disallowed_syntax?("ls -l")
false
iex> AI.Tools.Shell.Util.contains_disallowed_syntax?("ls | grep foo")
true
iex> AI.Tools.Shell.Util.contains_disallowed_syntax?("echo 'safe | quoted'")
false
"""
@spec contains_disallowed_syntax?(binary()) :: boolean()
def contains_disallowed_syntax?(cmd) when is_binary(cmd) do
try do
check_dangerous_patterns(cmd)
rescue
_ -> true
catch
:disallowed -> true
_ -> true
else
false -> false
true -> true
end
end
defp check_dangerous_patterns(cmd) do
# Check for various dangerous patterns
has_dangerous_characters?(cmd) or
has_unbalanced_quotes?(cmd) or
has_cmd_substitution_in_double_quotes?(cmd) or
(
unquoted_parts = extract_unquoted_parts(cmd, [], :unquoted, "")
Enum.any?(unquoted_parts, fn part ->
contains_dangerous_unquoted_pattern?(part)
end)
)
end
defp has_dangerous_characters?(cmd) do
# Check for dangerous characters that should be rejected regardless of context
# Here-document
# Shell escape sequences
String.contains?(cmd, ["\n", "\0"]) or
String.contains?(cmd, "<<") or
String.contains?(cmd, "$'") or
has_zero_width_space_in_unquoted?(cmd)
end
defp has_zero_width_space_in_unquoted?(cmd) do
# Check if zero-width space appears in unquoted parts
try do
unquoted_parts = extract_unquoted_parts(cmd, [], :unquoted, "")
Enum.any?(unquoted_parts, fn part ->
String.contains?(part, <<0x200B::utf8>>)
end)
catch
:unbalanced_quotes ->
# If quotes are unbalanced, just check if ZWSP exists anywhere (conservative)
String.contains?(cmd, <<0x200B::utf8>>)
end
end
defp has_unbalanced_quotes?(cmd) do
try do
extract_unquoted_parts(cmd, [], :unquoted, "")
false
catch
:unbalanced_quotes -> true
end
end
defp has_cmd_substitution_in_double_quotes?(cmd) do
check_double_quoted_cmd_subst(cmd, :unquoted)
end
defp check_double_quoted_cmd_subst("", _state), do: false
defp check_double_quoted_cmd_subst(<<char::utf8, rest::binary>>, state) do
case {state, char} do
{:unquoted, ?'} ->
check_double_quoted_cmd_subst(rest, :single_quoted)
{:unquoted, ?"} ->
check_double_quoted_cmd_subst(rest, :double_quoted)
{:single_quoted, ?'} ->
check_double_quoted_cmd_subst(rest, :unquoted)
{:double_quoted, ?"} ->
check_double_quoted_cmd_subst(rest, :unquoted)
{:double_quoted, ?\\} ->
# Skip escaped character
case rest do
<<_next::utf8, remaining::binary>> ->
check_double_quoted_cmd_subst(remaining, :double_quoted)
"" ->
false
end
{:double_quoted, ?$} ->
case rest do
# Found command substitution
<<"(", _::binary>> -> true
_ -> check_double_quoted_cmd_subst(rest, :double_quoted)
end
{:double_quoted, ?`} ->
# Check for backtick command substitution
case find_closing_backtick_simple(rest) do
# Found backtick command substitution
true -> true
false -> check_double_quoted_cmd_subst(rest, :double_quoted)
end
{_, _} ->
check_double_quoted_cmd_subst(rest, state)
end
end
defp find_closing_backtick_simple(str) do
String.contains?(str, "`")
end
defp extract_unquoted_parts("", acc, state, current) do
# If we end in a quoted state, quotes are unbalanced
case state do
:single_quoted -> throw(:unbalanced_quotes)
:double_quoted -> throw(:unbalanced_quotes)
:unquoted -> if current != "", do: [current | acc], else: acc
end
end
defp extract_unquoted_parts(<<char::utf8, rest::binary>>, acc, state, current) do
case {state, char} do
{:unquoted, ?'} ->
new_acc = if current != "", do: [current | acc], else: acc
extract_unquoted_parts(rest, new_acc, :single_quoted, "")
{:unquoted, ?"} ->
new_acc = if current != "", do: [current | acc], else: acc
extract_unquoted_parts(rest, new_acc, :double_quoted, "")
{:single_quoted, ?'} ->
extract_unquoted_parts(rest, acc, :unquoted, "")
{:double_quoted, ?"} ->
extract_unquoted_parts(rest, acc, :unquoted, "")
{:double_quoted, ?\\} ->
# Skip escaped char in double quotes
case rest do
<<_next::utf8, remaining::binary>> ->
extract_unquoted_parts(remaining, acc, :double_quoted, current)
"" ->
extract_unquoted_parts("", acc, :double_quoted, current)
end
{:unquoted, _} ->
extract_unquoted_parts(rest, acc, state, current <> <<char::utf8>>)
{_, _} ->
# In quoted context, ignore the character
extract_unquoted_parts(rest, acc, state, current)
end
end
defp contains_dangerous_unquoted_pattern?(part) do
# Check for dangerous shell patterns in unquoted text using regex
Regex.match?(~r/\||&&|\|\||;|>|<|`|\$\(|(?<!\&)\&(?!\&)|<\(|>\(/, part)
end
end