Fix memory leaks when tokens are missing

[simo5]

Description

In case we have slots advertized but the driver fails to return information or the token is not present we were leaking memory as the slot is not added to the array and the number of slots is not incremented.

Ensure the slot struct is freed in this case.

Fixes #462

Checklist

• Code modified for feature
• Test suite updated with functionality tests
• Test suite updated with negative tests
• Documentation updated

Reviewer's checklist:

• Any issues marked for closing are addressed
• There is a test suite reasonably covering new functionality or modifications
• This feature/change has adequate documentation added
• Code conform to coding style that today cannot yet be enforced via the check style test
• Commits have short titles and sensible commit messages
• Coverity Scan has run if needed (code PR) and no new defects were found

[DEX1999]

And what about leak when you allocate num elements on string 169, which equals to numbers of slots in system, and then if sctx->num == 0, which is equals to number of slots with tokens, you just return without freeing.

[Jakuje]

Good catch! I did not go deep into the p11prov_free_slots() but this condition needs to be probably removed to make sure the sctx->slots and sctx gets freed also when we fail before allocating the slots context:

pkcs11-provider/src/slot.c

Lines 351 to 353 in e064032

	if (sctx->num == 0) {
	return;
	}

[simo5]

And what about leak when you allocate num elements on string 169, which equals to numbers of slots in system, and then if sctx->num == 0, which is equals to number of slots with tokens, you just return without freeing.

It is a corner case not worth optimizing for IMHO.
Especially because I have a plan, in the future, to keep slots around that do not have token present as we have an interest in supporting token insertion in the future.

[simo5]

And what about leak when you allocate num elements on string 169, which equals to numbers of slots in system, and then if sctx->num == 0, which is equals to number of slots with tokens, you just return without freeing.

It is a corner case not worth optimizing for IMHO. Especially because I have a plan, in the future, to keep slots around that do not have token present as we have an interest in supporting token insertion in the future.

I misread the comment, sorry, pushed another change that drops the early return in the freeing function.

[Jakuje]

lgtm

[simo5]

ty!