Bug #28198 for Net-DNS: Net::DNS bug in v.60 with $_

Hi, There is a bug with the new Net::DNS v.60 - It improperly uses $_ inside, and thus overwrites the Callers $_ variable. One (easy) example is: | ice:~>perl -MNet::DNS -we 'use strict; | my $res=new Net::DNS::Resolver; | for (0){ | my $q=$res->send("freebsd.org","A"); | } | ' Modification of a read-only value attempted at /usr/local/lib/perl5/site_perl/5.8.8/mach/Net/DNS/Question.pm line 47. If you instead add a variable to the for loop, it runs as expected. CU, Sec P.S.: some system info, in case you need it: ice:~>uname -a FreeBSD ice 6.2-STABLE FreeBSD 6.2-STABLE #38: Sun Feb 25 09:20:09 CET 2007 root@ice:/export/obj/export/src/sys/ICE i386 ice:~>pkg_info -aI|grep Net-DNS p5-Net-DNS-0.60 Perl5 interface to the DNS resolver, and dynamic updates ice:~>perl -V Summary of my perl5 (revision 5 version 8 subversion 8) configuration: Platform: osname=freebsd, osvers=6.2-prerelease, archname=i386-freebsd-64int uname='freebsd ice 6.2-prerelease freebsd 6.2-prerelease #36: sun oct 1 00:50:35 cest 2006 root@:exportobjexportsrcsysice i386 ' config_args='-sde -Dprefix=/usr/local -Darchlib=/usr/local/lib/perl5/5.8.8/mach -Dprivlib=/usr/local/lib/perl5/5.8.8 -Dman3dir=/usr/local/lib/perl5/5.8.8/perl/man/man3 -Dman1dir=/usr/local/man/man1 -Dsitearch=/usr/local/lib/perl5/site_perl/5.8.8/mach -Dsitelib=/usr/local/lib/perl5/site_perl/5.8.8 -Dscriptdir=/usr/local/bin -Dsiteman3dir=/usr/local/lib/perl5/5.8.8/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Ui_malloc -Ui_iconv -Uinstallusrbinperl -Dcc=cc -Duseshrplib -Dccflags=-DAPPLLIB_EXP="/usr/local/lib/perl5/5.8.8/BSDPAN" -Doptimize=-O2 -fno-strict-aliasing -pipe -march=k6 -Ud_dosuid -Ui_gdbm -Dusethreads=n -Dusemymalloc=y -Duse64bitint' hint=recommended, useposix=true, d_sigaction=define usethreads=undef use5005threads=undef useithreads=undef usemultiplicity=undef useperlio=define d_sfio=undef uselargefiles=define usesocks=undef use64bitint=define use64bitall=undef uselongdouble=undef usemymalloc=y, bincompat5005=undef Compiler: cc='cc', ccflags ='-DAPPLLIB_EXP="/usr/local/lib/perl5/5.8.8/BSDPAN" -DHAS_FPSETMASK -DHAS_FLOATINGPOINT_H -fno-strict-aliasing -pipe -Wdeclaration-after-statement -I/usr/local/include', optimize='-O2 -fno-strict-aliasing -pipe -march=k6', cppflags='-DAPPLLIB_EXP="/usr/local/lib/perl5/5.8.8/BSDPAN" -DHAS_FPSETMASK -DHAS_FLOATINGPOINT_H -fno-strict-aliasing -pipe -Wdeclaration-after-statement -I/usr/local/include' ccversion='', gccversion='3.4.6 [FreeBSD] 20060305', gccosandvers='' intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=12345678 d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12 ivtype='long long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8 alignbytes=4, prototype=define Linker and Libraries: ld='cc', ldflags =' -Wl,-E -L/usr/local/lib' libpth=/usr/lib /usr/local/lib libs=-lgdbm -lm -lcrypt -lutil perllibs=-lm -lcrypt -lutil libc=, so=so, useshrplib=true, libperl=libperl.so gnulibc_version='' Dynamic Linking: dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags=' -Wl,-R/usr/local/lib/perl5/5.8.8/mach/CORE' cccdlflags='-DPIC -fPIC', lddlflags='-shared -L/usr/local/lib' Characteristics of this binary (from libperl): Compile-time options: MYMALLOC PERL_MALLOC_WRAP USE_64_BIT_INT USE_LARGE_FILES USE_PERLIO Locally applied patches: defined-or Built under freebsd Compiled at Oct 1 2006 02:28:53 @INC: /usr/local/lib/perl5/5.8.8/BSDPAN /usr/local/lib/perl5/site_perl/5.8.8/mach /usr/local/lib/perl5/site_perl/5.8.8 /usr/local/lib/perl5/site_perl/5.8.7 /usr/local/lib/perl5/site_perl/5.8.6 /usr/local/lib/perl5/site_perl/5.8.5 /usr/local/lib/perl5/site_perl/5.8.4 /usr/local/lib/perl5/site_perl/5.8.2 /usr/local/lib/perl5/site_perl/5.005 /usr/local/lib/perl5/site_perl /usr/local/lib/perl5/5.8.8/mach /usr/local/lib/perl5/5.8.8 . -- Failure is not an option. It comes bundled with your Microsoft product.

I've isolated and patched a somewhat obscure bug in the most recent (0.60) Net::DNS package. Calling mx() either as a function or a method overwrites the current value of $_ with the IP address of the DNS server that responded to the query. I haven't checked all the functions the package provides, but I know this effect is at least produced by the mx() function. Consider this code fragment: --- snip --- use strict; use warnings; use Net::DNS; my @a = ( { 'name' => 'www.google.com' }, { 'name' => 'www.yahoo.com' } ); foreach (@a) { print mx($_->{name}) . " is the ip for $_->{'name'}\n"; } --- snip --- Because the mx function overwrites the value of $_, we get a runtime error when we try to use $_ as a hash reference after the function call: Can't use string ("192.168.1.3") as a HASH ref while "strict refs" in use at - line 13. Further, since in the foreach loop $_ is an alias for each array entry, the mx function has also inadvertently overwritten the contents of @a. Since $_ in a true global variable, avoiding its use in the foreach only allows the alteration of $_ to manifest itself somewhere else. In my case it appeared 4 method calls above a call to Email::Valid::address(), which uses Net::DNS internally to verify that the domain name exists. Below are the 3 places I've found where alterations to $_ occur and the alterations I made to prevent it. In Net::DNS::Question::new() replace my $qname = defined ($_ = shift) ? $_ : ''; with my $qname = shift; $qname = '' unless defined ($qname); In Net::DNS::Resolver::Base in _ip_is_ipv4() and _ip_is_ipv6() replace $_ = shift; with local $_ = shift; This effect is most likely platform neutral, but it has appeared for me in perl 5.8.8 on Gentoo and CentOs Linux, with the above snippet pasted directly into perl and under various minor revisions of mod_perl and apache 2. Please let me know if there is anything I can do to help.