#!/usr/bin/env perl

# Find functions making recursive calls to themselves.
# (Multiple recursion where a() calls b() which calls a() not covered.)
#
# When the recursion depth might depend on data controlled by the attacker in
# an unbounded way, those functions should use interation instead.
#
# Typical usage: scripts/recursion.pl library/*.c

use warnings;
use strict;

use utf8;
use open qw(:std utf8);

# exclude functions that are ok:
# - mpi_write_hlp: bounded by size of mbedtls_mpi, a compile-time constant
# - x509_crt_verify_child: bounded by MBEDTLS_X509_MAX_INTERMEDIATE_CA
my $known_ok = qr/mpi_write_hlp|x509_crt_verify_child/;

my $cur_name;
my $inside;
my @funcs;

die "Usage: $0 file.c [...]\n" unless @ARGV;

while (<>)
{
    if( /^[^\/#{}\s]/ && ! /\[.*]/ ) {
        chomp( $cur_name = $_ ) unless $inside;
    } elsif( /^{/ && $cur_name ) {
        $inside = 1;
        $cur_name =~ s/.* ([^ ]*)\(.*/$1/;
    } elsif( /^}/ && $inside ) {
        undef $inside;
        undef $cur_name;
    } elsif( $inside && /\b\Q$cur_name\E\([^)]/ ) {
        push @funcs, $cur_name unless /$known_ok/;
    }
}

print "$_\n" for @funcs;
exit @funcs;