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From Ed.Edding...@priorityhealth.com
Subject [MP2] Seg Fault in Registry script "print" using output filter handler
Date Wed, 15 Nov 2006 21:47:56 GMT

I'm getting seg faults within "print" of ModPerl::Registry script while
using an output filter handler. The output filter is run during the
script's "print" statement when the printed string is > ~8kb. Debugging
shows the seg fault occurs AFTER the output filter handler has completed
successfully, but BEFORE the print statement completes. GDB backtrace is
below. Perl modules CGI.pm and LWP::UserAgent seem to be causal in
generating the seg fault.

Here is the somewhat complicated recipe that produces the seg fault
reliably. 

1. ModPerl::Registry script using CGI.pm header() and a print statement
that includes a comma separated (list) of strings > 8kb.
2. An output filter handler that uses LWP::UserAgent to make an HTTP
request.

Caveats:
    - Only occurs in an Apache child that hasn't already loaded these
modules (CGI, LWP::UserAgent) and dependents.
    - Occurs in single process mode (-X) on both static and dynamically
linked builds.

Example script/filter and system details are below. I can provide more
info if needed. I'm currently testing other module versions. Can anyone
suggest a fix or workaround? 

Thanks!
Ed Eddington
Sr. Software Engr - Web Development
Priority Health - Grand Rapids, MI


GDB BACKTRACE

(gdb) continue
Continuing.

Program received signal SIGSEGV, Segmentation fault.
Perl_do_print (my_perl=0x8497ae0, sv=0x1, fp=0x86ee6c8) at doio.c:1321
1321    doio.c: No such file or directory.
        in doio.c
(gdb) bt
#0  Perl_do_print (my_perl=0x8497ae0, sv=0x1, fp=0x86ee6c8) at
doio.c:1321
#1  0x00375da8 in Perl_pp_print (my_perl=0x8497ae0) at pp_hot.c:624
#2  0x00362973 in Perl_runops_debug (my_perl=0x8497ae0) at dump.c:1452
#3  0x0031d812 in S_call_body (my_perl=0x8497ae0, myop=0xbff8d050,
is_eval=0) at perl.c:2364
#4  0x0031d4dd in Perl_call_sv (my_perl=0x8497ae0, sv=0x0, flags=4) at
perl.c:2282
#5  0x0807a257 in modperl_callback (my_perl=0x8497ae0,
handler=0x92bf1d8, p=0x93522b8, r=0x93522f0, s=0x92c0ef0,
args=0x932c878)
    at modperl_callback.c:100
#6  0x0807a997 in modperl_callback_run_handlers (idx=6, type=4,
r=0x93522f0, c=0x0, s=0x92c0ef0, pconf=0x0, plog=0x0, ptemp=0x0, 
    run_mode=MP_HOOK_RUN_FIRST) at modperl_callback.c:261
#7  0x0807af07 in modperl_callback_per_dir (idx=6, r=0x1,
run_mode=MP_HOOK_RUN_FIRST) at modperl_callback.c:368
#8  0x08074aa1 in modperl_response_handler_run (r=0x93522f0, finish=0)
at mod_perl.c:994
#9  0x08074d2b in modperl_response_handler_cgi (r=0x93522f0) at
mod_perl.c:1089
#10 0x080f5040 in ap_run_handler ()
#11 0x080f579e in ap_invoke_handler ()
#12 0x080c55da in ap_process_request ()
#13 0x080bfa06 in ap_process_http_connection ()
#14 0x08101ab8 in ap_run_process_connection ()
#15 0x08101ea3 in ap_process_connection ()
#16 0x080f38fb in child_main ()
#17 0x080f39d2 in make_child ()
#18 0x080f3af8 in startup_children ()
#19 0x080f3efe in ap_mpm_run ()
#20 0x080fac06 in main ()



EXAMPLE SCRIPT

#!/usr/bin/perl
use strict;
use Carp;

use CGI qw(:standard);

warn "TEST START...";

# doesn't matter if you have this line in the print stmt or not
header(-type=>"text/html");

my $head = '<HTML>';
my $foot = '</html>';
my $string = &string;

print $head,$string,br,$foot;

warn "TEST DONE--------------------------";

sub string {
    my $string;
    for (1..8200) {
        $string.= 'A';
    }
    return $string;
}


EXAMPLE FILTER:

#file:Apache2/SimpleFilter.pm
#--------------------------------
package PH::Apache2::SimpleFilter;

use strict;
use warnings;

use base qw(Apache2::Filter);

use APR::Brigade ();
use APR::Bucket ();

use Apache2::Const -compile => 'OK';
use APR::Const     -compile => ':common';

sub handler : FilterRequestHandler {
    my ($f, $bb) = @_;

    my $bb_ctx = APR::Brigade->new($f->c->pool, $f->c->bucket_alloc);

    while (!$bb->is_empty) {
        my $b = $bb->first;

        $b->remove;

        if ($b->is_eos) {
            $bb_ctx->insert_tail($b);
            last;
        }

        if ($b->read(my $data)) {
            #Do Nothing
            #$data = join "",
            #    map {scalar(reverse $_), "\n"} split "\n", $data;
            $b = APR::Bucket->new($bb->bucket_alloc, $data);
        }
        use LWP::UserAgent;
        my $ua = LWP::UserAgent->new();
        my $uri = 'http://www.yahoo.com';
        my $response = $ua->get($uri);
        warn "LWP got $response";

        $bb_ctx->insert_tail($b);
  }

  my $rv = $f->next->pass_brigade($bb_ctx);
  return $rv unless $rv == APR::Const::SUCCESS;

  Apache2::Const::OK;
}
1;

-----------------------------------------
SYSTEM DETAILS:
-----------------------------------------

mod_perl version 2.000001
LWP - 5.803
LWP::UserAgent - 2.03
CGI - 3.25
Apache2::Request - 2.08


$ uname -a
Linux molly 2.6.9-42.ELsmp #1 SMP Wed Jul 12 23:27:17 EDT 2006 i686 i686
i386 GNU/Linux


DYNAMIC APACHE

$ /opt/apache2/bin/httpd -l
Compiled in modules:
  core.c
  prefork.c
  http_core.c
  mod_so.c

$ /opt/apache2/bin/httpd -V
Server version: Apache/2.0.59
Server built:   Jul 28 2006 15:42:08
Server's Module Magic Number: 20020903:12
Server loaded:  APR 0.9.12, APR-UTIL 0.9.12
Compiled using: APR 0.9.12, APR-UTIL 0.9.12
Architecture:   32-bit
Server compiled with....
 -D APACHE_MPM_DIR="server/mpm/prefork"
 -D APR_HAS_SENDFILE
 -D APR_HAS_MMAP
 -D APR_HAVE_IPV6 (IPv4-mapped addresses enabled)
 -D APR_USE_SYSVSEM_SERIALIZE
 -D APR_USE_PTHREAD_SERIALIZE
 -D SINGLE_LISTEN_UNSERIALIZED_ACCEPT
 -D APR_HAS_OTHER_CHILD
 -D AP_HAVE_RELIABLE_PIPED_LOGS
 -D HTTPD_ROOT="/opt/apache2"
 -D SUEXEC_BIN="/opt/apache2/bin/suexec"
 -D DEFAULT_PIDLOG="logs/httpd.pid"
 -D DEFAULT_SCOREBOARD="logs/apache_runtime_status"
 -D DEFAULT_LOCKFILE="logs/accept.lock"
 -D DEFAULT_ERRORLOG="logs/error_log"
 -D AP_TYPES_CONFIG_FILE="conf/mime.types"
 -D SERVER_CONFIG_FILE="conf/httpd.conf"


STATIC APACHE (built with debug flags)

$ /opt/apache2-debug/bin/httpd -l
Compiled in modules:
  core.c
  mod_perl.c
  mod_access.c
  mod_auth.c
  mod_include.c
  mod_log_config.c
  mod_env.c
  mod_headers.c
  mod_setenvif.c
  mod_proxy.c
  proxy_connect.c
  proxy_ftp.c
  proxy_http.c
  mod_ssl.c
  prefork.c
  http_core.c
  mod_mime.c
  mod_dav.c
  mod_status.c
  mod_autoindex.c
  mod_asis.c
  mod_cgi.c
  mod_dav_fs.c
  mod_negotiation.c
  mod_dir.c
  mod_imap.c
  mod_actions.c
  mod_userdir.c
  mod_alias.c
  mod_rewrite.c
  mod_so.c

$ /opt/apache2-debug/bin/httpd -V
Server version: Apache/2.0.59
Server built:   Nov  3 2006 13:36:26
Server's Module Magic Number: 20020903:12
Server loaded:  APR 0.9.12, APR-UTIL 0.9.12
Compiled using: APR 0.9.12, APR-UTIL 0.9.12
Architecture:   32-bit
Server compiled with....
 -D APACHE_MPM_DIR="server/mpm/prefork"
 -D APR_HAS_SENDFILE
 -D APR_HAS_MMAP
 -D APR_HAVE_IPV6 (IPv4-mapped addresses enabled)
 -D APR_USE_SYSVSEM_SERIALIZE
 -D APR_USE_PTHREAD_SERIALIZE
 -D SINGLE_LISTEN_UNSERIALIZED_ACCEPT
 -D APR_HAS_OTHER_CHILD
 -D AP_HAVE_RELIABLE_PIPED_LOGS
 -D HTTPD_ROOT="/opt/apache2-debug"
 -D SUEXEC_BIN="/opt/apache2-debug/bin/suexec"
 -D DEFAULT_PIDLOG="logs/httpd.pid"
 -D DEFAULT_SCOREBOARD="logs/apache_runtime_status"
 -D DEFAULT_LOCKFILE="logs/accept.lock"
 -D DEFAULT_ERRORLOG="logs/error_log"
 -D AP_TYPES_CONFIG_FILE="conf/mime.types"
 -D SERVER_CONFIG_FILE="conf/httpd.conf"

$ /usr/bin/ldd  /opt/apache2/bin/httpd
        libz.so.1 => /usr/lib/libz.so.1 (0x00ab2000)
        libssl.so.4 => /lib/libssl.so.4 (0x00129000)
        libcrypto.so.4 => /lib/libcrypto.so.4 (0x006d7000)
        libgssapi_krb5.so.2 => /usr/lib/libgssapi_krb5.so.2 (0x00de9000)
        libkrb5.so.3 => /usr/lib/libkrb5.so.3 (0x00227000)
        libcom_err.so.2 => /lib/libcom_err.so.2 (0x00de4000)
        libk5crypto.so.3 => /usr/lib/libk5crypto.so.3 (0x0028e000)
        libresolv.so.2 => /lib/libresolv.so.2 (0x00ac4000)
        libaprutil-0.so.0 => /opt/apache2/lib/libaprutil-0.so.0
(0x00111000)
        libexpat.so.0 => /opt/apache2/lib/libexpat.so.0 (0x0099d000)
        libapr-0.so.0 => /opt/apache2/lib/libapr-0.so.0 (0x00a54000)
        librt.so.1 => /lib/tls/librt.so.1 (0x002b1000)
        libm.so.6 => /lib/tls/libm.so.6 (0x00963000)
        libcrypt.so.1 => /lib/libcrypt.so.1 (0x002fc000)
        libnsl.so.1 => /lib/libnsl.so.1 (0x002cd000)
        libpthread.so.0 => /lib/tls/libpthread.so.0 (0x0015d000)
        libdl.so.2 => /lib/libdl.so.2 (0x0095d000)
        libc.so.6 => /lib/tls/libc.so.6 (0x00830000)
        /lib/ld-linux.so.2 (0x00817000)


$ /opt/perl-5.8/bin/perl -V
Summary of my perl5 (revision 5 version 8 subversion 7) configuration:
  Platform:
    osname=linux, osvers=2.4.21-32.0.1.elsmp,
archname=i686-linux-thread-multi
    uname='linux molly 2.4.21-32.0.1.elsmp #1 smp tue may 17 17:52:23
edt 2005 i686 i686 i386 gnulinux '
    config_args='-der'
    hint=previous, useposix=true, d_sigaction=define
    usethreads=define use5005threads=undef useithreads=define
usemultiplicity=define
    useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
    use64bitint=undef use64bitall=undef uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -g -fPIC
-I/opt/perl-5.8/local/include -DDEBUGGING -fno-strict-aliasing -pipe
-I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-g -O2 ',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -g -fPIC
-I/opt/perl-5.8/local/include -DDEBUGGING -fno-strict-aliasing -pipe
-I/usr/local/include -D_REENTRANT -D_GNU_SOURCE -g -fPIC
-I/opt/perl-5.8/local/include -DDEBUGGING -fno-strict-aliasing -pipe
-I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64'
    ccversion='', gccversion='3.2.3 20030502 (Red Hat Linux 3.2.3-52)',
gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t',
lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib /usr/ccs/lib
    libs=-lnsl -ldb -ldl -lm -lcrypt -lutil -lpthread -lc
    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
    libc=/lib/libc-2.3.2.so, so=so, useshrplib=true, libperl=libperl.so
    gnulibc_version='2.3.2'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E
-Wl,-rpath,/opt/perl-5.8/lib/5.8.7/i686-linux-thread-multi/CORE'
    cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'


Characteristics of this binary (from libperl): 
  Compile-time options: DEBUGGING MULTIPLICITY USE_ITHREADS
                        USE_LARGE_FILES PERL_IMPLICIT_CONTEXT
  Built under linux
  Compiled at Sep 12 2005 12:52:00
  @INC:
    /opt/perl-5.8/lib/5.8.7/i686-linux-thread-multi
    /opt/perl-5.8/lib/5.8.7
    /opt/perl-5.8/lib/site_perl/5.8.7/i686-linux-thread-multi
    /opt/perl-5.8/lib/site_perl/5.8.7
    /opt/perl-5.8/lib/site_perl
    .


HTTPD2.CONF (relavent pieces included in order)

PerlOutputFilterHandler PH::Apache2::SimpleFilter
...
    <Location /prog >
        ProxyPass !
        SetHandler perl-script
        PerlResponseHandler ModPerl::Registry
        Options ExecCGI
    </Location>


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