Increased MBEDTLS_BEFORE_COLON (size of temporary buffer) to 32

[Mario-Klebsch]

Description

Fix for Ticket #4894:

• The buffer size is increased to 32
• An asseretion is added to check for buffer to small in development builds

PR checklist

• changelog not required because: I have no idea, what to write
• tests provided (as comment in mbedtls_x509_crt_info calls mbedtls_x509_key_size_helper with buffer that's too small #4894)

[mpg]

Thanks for your contribution!

However it needs to include an automated non-regression test, as part of test_suite_x509parse. See https://mbed-tls.readthedocs.io/en/latest/kb/development/test_suites/ and please feel free to ask questions if anything's not clear enough.

[mpg]

We don't use assert in the library.

[Mario-Klebsch]

The purpose of assert()ions is to signal errors in the internal logic of some software. In this case, supplying an insuffently sized buffer to mbedtls_x509_key_size_helper() in an error in the program logic. This is the reason, why I added an assertion.

Just remove it from my contribution, if you don't want to use this extra instrumentation in your code.

[mpg]

Like several libraries, we have a rule not to use assert(), but instead return an error and let the program decide what to do with it (termination may not be the best response).

Just remove it from my contribution, if you don't want to use this extra instrumentation in your code.

The way our review process works is that PR authors are supposed to make changes if needed. We don't normally merge patches that will need to be modified later.