Re: PHP 7.4 BC break with openssl_random_pseudo_bytes()

Den 2019-11-06 kl. 20:44, skrev Jakub Zelenka:

On Wed, Oct 30, 2019 at 6:33 PM Jakub Zelenka <bukka@php.net> wrote:

On Wed, 30 Oct 2019, 18:32 Jakub Zelenka, <bukka@php.net> wrote:

On Mon, 23 Sep 2019, 14:02 Nikita Popov, <nikita.ppv@gmail.com> wrote:

On Mon, Sep 23, 2019 at 2:52 PM Christian Schneider < cschneid@cschneid.com> wrote:

Hi, I just noted (too late in the process, I know) that openssl_random_pseudo_bytes(0) now throws an exception. This breaks code like

         $ivsize = openssl_cipher_iv_length($method);
         $iv = openssl_random_pseudo_bytes($ivsize);
         $data = openssl_encrypt($string, $method, $key,

OPENSSL_RAW_DATA,

$iv); if $method is 'aes-256-ecb' because $ivsize is 0. I do realize that ECB mode ciphers are deprecated but having them

throw an

exception indirectly via openssl_random_pseudo_bytes() seems a bit

strange,

even in the context of security. I checked the RFC https://wiki.php.net/rfc/improve-openssl-random-pseudo-bytes and it doesn't mention this BC break: "False-checks on the return value of openssl_random_pseudo_bytes()

will do

nothing since the function fails closed. Usage of $crypto_strongwill generate errors." While I would have preferred the exception to be thrown only when

$ivsize

is not an integer or less than 0 but I guess this cannot be changed at

the

RC stage. I would recommend though that we aim to keep BC breaks to what's

mentioned

in RFCs.

This was noted during the PR review in: https://github.com/php/php-src/pull/3649#discussion_r230598754 Especially in conjunction with your example, I think we should revert this part an make openssl_random_pseudo_bytes(0) return "" without exception or warning. Ideally we'd adjust random_bytes() to do the same.

I agree this should be reverted for 7.4 at least as it's a BC and wasn't really in RFC. It really doesn't matter if it's a good thing or not as it's a BC that we shouldn't do in minor release.

I mean BC break ofc... :)

I was thinking about the revert but after reading the RFC again, I don't think it would be right thing to do. Although it's a bit generic and doesn't mention when it can fail, it states that the exception is thrown on fail. We always considered this case as a fail because it returned false so it's kind of covered. It would be also quite late to do such changes in 7.4 and I guess RM wouldn't allow it anyway. It's basically BC break that went through the RFC which is probably acceptable. I have to say that the RFC wasn't really well done as the implementation followed which caused this omission. We should really look properly to the implementation when creating RFC so it's more detailed and doesn't cause omission like this. Cheers Jakub

Hi, So, what's the RM view on this? I think one should take into account the total amount of deprecations & BC breakages in 7.4. If they are many, it's a pity to add things making code break even more. Another thing to consider is that when upgrading and there are breakages one doesn't upgrade, instead staying on an old PHP version. So providing an easier upgrade path also has value! Also, is there an estimate on how this BC breakage would affect libraries? Or to phrase it differently is it a common code pattern that now will generate exceptions instead? r//Björn L