threadsafe php crashes too easily

Posted 1 year ago by Hajo Locke — view source

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Hello List,

i hope this is the right place to get helped. I have a promising setup
for testing purposes, but unfortunately i ran quick into problems.

I compiled a minimal libphp7.so (7.2.1) using this line:
./configure --disable-all --enable-static --prefix=/usr
--with-apxs2=/usr/bin/apxs2 --enable-maintainer-zts

I enabled threadsafety to use this libphp7.so in apache 2.4 with a
threaded mpm like worker or event. the plan is to just load it with
LoadModule in apache but not to use it.
the real php-processing is done by a fastcgi-setup in apache using
php-fpm (not needed to reproduce error). the idea is to support
php_value/php_flag etc. in .htaccess files for my users even if they use
a fastcgi-setup. all i need is htscanner extension for php-cgi and just
a loaded libphpx.so to register these directives in apache. may be this
is a dump idea, but i have thousands of users who use libphpx.so and a
huge number of .htaccess with php_value/php_flag directives. currently i
see no possibility to tell users to switch to .user.ini

First steps are really successful and all worked well. Even benchmarking
the system with massrequests did not show any error. php_value/php_flag
in .htaccess showed expected behaviour when requesting a php-file using
fastcgi.
Unfortunately there is only a small change to see lots of segfaults in
errorlog: Just enable a php_value directive in VHost-Config for this
particular VHost along with a php_value directive in .htaccess in
docroot of this VHost. It is not needed to request a php-file, just
requesting a small static file is enough. The smaller the requested file
and higher requests per second the higher is count of segfaults.

I knew that threadsafe-compiled php is a problematic thing and recommend
mpm is prefork when not using a fastcgi-configuration, but iam surprised
that i see the crashes so easily. I used a minimal php and it seems
problem occurs just by reading and applying the values set by php_value
for particular request.

Do i have a chance to get this setup safe?

Thanks a lot,
Hajo

Posted 1 year ago by Rowan Collins — view source

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the idea is to support php_value/php_flag etc. in .htaccess files for my
users even if they use a fastcgi-setup

Just a thought, but if I understand you rightly, you just need to have
Apache completely ignore the php_value and php_flag lines, so would it work
to build a custom Apache extension which just registered for those
directives and did nothing?

I know it sounds complicated, but I was able to hack in support for the
UndefMacro keyword into an old version of mod_macro (result here:
https://github.com/IMSoP/mod_macro) and Apache ships with a very
user-friendly build tool called APXS [
https://httpd.apache.org/docs/2.4/programs/apxs.html]. It would probably
fairly simple to whip up a "mod_notphp" which does nothing but register
those two directives to empty callbacks.

Regards,

Rowan Collins
[IMSoP]

Posted 1 year ago by [email protected] — view source

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Hello List,

i hope this is the right place to get helped. I have a promising
setup
for testing purposes, but unfortunately i ran quick into problems.

I compiled a minimal libphp7.so (7.2.1) using this line:
./configure --disable-all --enable-static --prefix=/usr
--with-apxs2=/usr/bin/apxs2 --enable-maintainer-zts

The enable mantainer zts should not be needed. The apache module tries
to identify the configuration an enable thread-safety automatically if
needed. I'd suggest removng the option and checking configure output
and config.log and trying to see what it identifies ... however there's
not much love for mpm_worker on the PHP side :-)

If all you want is to prevent apache from complaining about
php_value/php_flag directives for handling them elsewhere I'd suggest
writing a simple apache module which simply registers those settings
and does nothing else. Seems way less problematic.

Can be done mostly by copy and paste from that site:
http://httpd.apache.org/docs/2.4/developer/modguide.html#configuration

johannes

Posted 1 year ago by Hajo Locke — view source

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Hello,

thank you all for your suggestions.

Am 26.01.2018 um 13:21 schrieb Johannes Schlüter:

Hello List,

i hope this is the right place to get helped. I have a promising
setup
for testing purposes, but unfortunately i ran quick into problems.

I compiled a minimal libphp7.so (7.2.1) using this line:
./configure --disable-all --enable-static --prefix=/usr
--with-apxs2=/usr/bin/apxs2 --enable-maintainer-zts
The enable mantainer zts should not be needed. The apache module tries
to identify the configuration an enable thread-safety automatically if
needed. I'd suggest removng the option and checking configure output
and config.log and trying to see what it identifies ... however there's
not much love for mpm_worker on the PHP side :-)

If all you want is to prevent apache from complaining about
php_value/php_flag directives for handling them elsewhere I'd suggest
writing a simple apache module which simply registers those settings
and does nothing else. Seems way less problematic.
Yes, i thought about that a few das ago, but believed it is to hard for
me. But you are right, it is enought to tell apache about the
directives, there is no need to add some further funtionality.
Iam not a programmer, just sysadmin. Following your
sapi/apache2handler/apache_config.c i was able to put php_value etc.
into this example-module and did a first run.
To my surprise this was successful. Configtest was ok, and on php-fpm
side your htscanner still worked.
It seems this is a very promising way and i will invest more time in it
to get this stable.
Thank you all.

Can be done mostly by copy and paste from that site:
http://httpd.apache.org/docs/2.4/developer/modguide.html#configuration

johannes

Thanks,
Hajo

Posted 1 year ago by Anatol Belski — view source

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Hi,

-----Original Message-----
From: Hajo Locke [mailto:[email protected]]
Sent: Friday, January 26, 2018 12:43 PM
To: [email protected]
Subject: [PHP-DEV] threadsafe php crashes too easily

Hello List,

i hope this is the right place to get helped. I have a promising setup for testing
purposes, but unfortunately i ran quick into problems.

I compiled a minimal libphp7.so (7.2.1) using this line:
./configure --disable-all --enable-static --prefix=/usr
--with-apxs2=/usr/bin/apxs2 --enable-maintainer-zts

I enabled threadsafety to use this libphp7.so in apache 2.4 with a threaded mpm
like worker or event. the plan is to just load it with LoadModule in apache but
not to use it.
the real php-processing is done by a fastcgi-setup in apache using php-fpm (not
needed to reproduce error). the idea is to support php_value/php_flag etc. in
.htaccess files for my users even if they use a fastcgi-setup. all i need is
htscanner extension for php-cgi and just a loaded libphpx.so to register these
directives in apache. may be this is a dump idea, but i have thousands of users
who use libphpx.so and a huge number of .htaccess with php_value/php_flag
directives. currently i see no possibility to tell users to switch to .user.ini

First steps are really successful and all worked well. Even benchmarking the
system with massrequests did not show any error. php_value/php_flag in
.htaccess showed expected behaviour when requesting a php-file using fastcgi.
Unfortunately there is only a small change to see lots of segfaults in
errorlog: Just enable a php_value directive in VHost-Config for this particular
VHost along with a php_value directive in .htaccess in docroot of this VHost. It is
not needed to request a php-file, just requesting a small static file is enough. The
smaller the requested file and higher requests per second the higher is count of
segfaults.

I just made a quick try with the way you've described - php_value once in httpd.conf and in .htaccess, but I see no crash. Perhaps you could file a ticket with a more detailed description and a backtrace you currently get.

I knew that threadsafe-compiled php is a problematic thing and recommend
mpm is prefork when not using a fastcgi-configuration, but iam surprised that i
see the crashes so easily. I used a minimal php and it seems problem occurs just
by reading and applying the values set by php_value for particular request.

It depends on what you do. Some dependencies or even functions in the C runtime are not thread safe, one has to be aware what is used by an application.

Thanks

Anatol