Fix GH-12232: FPM: segfault dynamically loading extension without opcache

[bukka]

This is alternative fix that uses zend_interned_strings_switch_storage before using php_dl to make sure that permanent internet string storage is used instead of request storage. Suggested by @dstogov in #12233

[dstogov]

I'm not sure, if the fact that extension interned strings are not going to be copied by accel_copy_permanent_strings() may make critical problems.

A potential problem, that during caching, opcache may keep a reference to such string and then another process may use this "invalid" reference. Can you please check if this is possible?

[bukka]

@dstogov Ok let me first check if I understood correctly what you see as a potential problem. Is it that the interned string
(module name in our case) stored in permanent hash table and opcache could potentially cache the string reference
to shm which could then be used by other procs and cause a crash? That means that opcache would have to relay on the
IS_STR_INTERNED flag instead of checking accel interned range?

If so, I have done some checking and reading of opcache code. From what I see all strings should go through
zend_accel_store_interned_string (specifically the ones in zend_persist_zval where I would be looking for this
sort of issue) which however uses IS_ACCEL_INTERNED check so it should be ok as it checks the memory range and should not treat permanent interned string as accell interned string (meaning it should not store its reference but copy the whole
string instead).

Are there any other places that I should check or did I miss anything in the above?

[dstogov]

Are there any other places that I should check or did I miss anything in the above?

I think your analyses should be enough.