C set attribute value

[konstantinpersidskiy]

Checklist

• PKCS#11 module is tested
• Windows minidriver is tested
• macOS tokend is tested

Hello,
PKCS11 standard v. 2.40 (https://docs.oasis-open.org/pkcs11/pkcs11-base/v2.40/os/pkcs11-base-v2.40-os.pdf) states that default value for CKO_DATA object's CKA_VALUE is empty (4.5.2, page 42). That points to the possibility of modifying this attribute for these objects via C_SetAttributeValue (same can be seen in the current code for object's id).
These commits allow creating data objects with empty CKA_VALUE and modifying it later.

[frankmorgner]

The change looks OK in general, but I don't know how to test this. What tests did you run?

[konstantinpersidskiy]

I wrote a small test using opensc-pkcs11 that creates a data object with empty CKA_VALUE, then finds this object and modifies it's CKA_VALUE to non-empty. I ran it on RutokenS and RutokenECP tokens and checked tokens' file structure for data object EF and changes I expected in DODF.
I can upload my test if you like

[konstantinpersidskiy]

https://gist.github.com/konstantinpersidskiy/bc6824101a85fb2e8ce11743183d04a9
That's my test, to compile change path to opensc-pkcs11.so in dlopen.
@frankmorgner , is that enough?

[frankmorgner]

missing error check. you could also use realloc()

[frankmorgner]

@konstantinpersidskiy for testing, the example is more than I've expected. Actually, I was referring to the checklist above and wanted to know what card you tested with what functionality.

Anyway, please see the above comment about the missing error check.