On 10/1/24 9:32 AM, Ervin Hegedüs wrote:
> Hi there,
>
> I hope this is a good forum to ask my question.
>
> We (mod_security2 developers) use mutex locks. Thiscode snippet was added
> recently:
>
> https://github.com/owasp-modsecurity/ModSecurity/blob/v2/master/apache2/modsecurity.c#L125-L168
>
> As you can see, we create locks with these functions:
>
> apr_temp_dir_get()
> apr_file_mktemp()
> apr_global_mutex_create()
>
> This wrapper (acquire_global_lock()) works on Linux, but it seems to crash on
> FreeBSD:
> https://github.com/owasp-modsecurity/ModSecurity/issues/3255
>
> I did some investigation and I found that after the apr_file_mktemp() returns
> with success and the created file name is given to
> apr_global_mutex_create() then it removes that.
>
> In this comment:
> https://github.com/owasp-modsecurity/ModSecurity/issues/3255#issuecomment-2383132160
> I explained the results (with gdb and truss).
>
> My question is: what is the expected way to use file mutexes?
>
> Thanks for your help,
Have a look at
https://httpd.apache.org/docs/2.4/mod/core.html#mutex
https://github.com/apache/httpd/blob/trunk/include/util_mutex.h#L156
https://github.com/apache/httpd/blob/trunk/include/util_mutex.h#L181
and as example
https://github.com/apache/httpd/blob/trunk/modules/ssl/mod_ssl.c#L456
https://github.com/apache/httpd/blob/trunk/modules/ssl/ssl_engine_mutex.c#L50
If you want to go for an APR only approach keep in mind that the apr methods
create the lock file if needed
either with the name you specified or they create it in /tmp via apr_file_mktemp
It should not exist.
See
https://github.com/apache/apr/blob/1.7.x/locks/unix/proc_mutex.c#L1051
https://github.com/apache/apr/blob/1.7.x/locks/unix/proc_mutex.c#L1200
Regards
Rüdiger
