Bug #71915 [Asn]: openssl_random_pseudo_bytes is not "fork-safe"

Edit report at https://bugs.php.net/bug.php?id=71915&edit=1 ID: 71915 Updated by: bukka@php.net Reported by: mathieuk at gmail dot com Summary: openssl_random_pseudo_bytes is not "fork-safe" Status: Assigned Type: Bug Package: OpenSSL related Operating System: any PHP Version: 5.6.19 Assigned To: bukka Block user comment: N Private report: N New Comment: I'm still thinking (read didn't have time to think about it much yet :) ) what would be the best solution and will try to play with both patches later when I have time. Here are just few thoughts. - The perf hit that you say is actually limited for fpm quite considerably because you have got a pool of processes so there is not so much forking and one process is used for many requests. In case of prefork, I'm not sure if people that use it actually care about perf :) - I'm wondering where you see that OpenSSL adds time to the rand pool. I checked code and the only version that does so is current master (1.1 that is not supported by PHP yet). All others add only PID. I might have missed it thought. Could you point me to the code where it is added and could you point me to some article that explains why adding time doesn't help either. I'm just curious... - The Rand is not used just in openssl_random_pseudo_bytes but also in private key generation (if you add partial parameters) and sealing as well so there are few more places but that could be addressed of course in your patch too. - There is actually another thing on pthread_atfork that wasn't mentioned. OpenSSL would now require linking of libpthread which should be probably checked with packagers and RM's as it's a new lib dependency for openssl ext (especially if that should go to bug fixing release) I will try to send an update when I get a bit more time to look into it. Previous Comments: ------------------------------------------------------------------------ [2016-03-31 13:21:55] mathieuk at gmail dot com @bukka Any idea yet on what direction you'd like to go? To follow up on some things: People are asking whether just reseeding on fork() isn't the way to go. @krakjoe even implemented [a POC PR](https://github.com/php/php-src/pull/1844) - although it's with PID and time (which doesn't help). I have some doubts about whether we are able to register that pthread_atfork callback soon enough for all SAPIs for it to be usable. Even if we are, that means that all requests are now getting a perf-hit regardless of if you even use openssl. That's something I tried to prevent in my PR. ------------------------------------------------------------------------ [2016-03-29 20:42:22] bukka@php.net Ah I see what's the issue - finally read the links... :). Reading and thinking about it a bit more, the RAND_poll is probably reasonable. It would be good to know if there is any visible slow down though. Not that it would be a blocker but rather to see if we should have also consider some other solutions like addressing that in the SAPI's possibly (which might not be a great idea though). Anyway I will have to think about it a bit more so will leave this for a couple of days. ------------------------------------------------------------------------ [2016-03-29 19:33:24] mathieuk at gmail dot com I've moved it to https://github.com/php/php-src/pull/1843 @bukka Seeding with PID and time already happens after each call to RAND_bytes() and is what caused this behaviour in the first place. Apache's mod_ssl calls RAND_seed() with a few bytes from /dev/urandom (or egd) for each request - we could do that instead, but it seems like that's pretty much what RAND_poll() does. What are you seeing as the heavy part of RAND_poll? @krakjoe Right. This would work fine in mod_php, but maybe not FPM. I could force the bool to false in PHP_RINIT_FUNCTION(openssl). Think that'd work better? ------------------------------------------------------------------------ [2016-03-29 19:09:22] bukka@php.net Yeah there seems to be missing global init which should reset the value for each request (PHP_GINIT_FUNCTION). Then it should be fine and the entropy would be added for the first call of the openssl_random_pseudo_bytes in the request. It means it can be added multiple time if the same process is used for more requests (fpm) which I'm not sure is ideal but might not be an issue. Again I might be wrong. ------------------------------------------------------------------------ [2016-03-29 18:54:12] krakjoe@php.net Well, COW duplicated ... the same data whatever ... ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at https://bugs.php.net/bug.php?id=71915 -- Edit this bug report at https://bugs.php.net/bug.php?id=71915&edit=1