Depends on tss2-esys >= 2.4

[dkobras]

Since the call to Esys_TR_GetTpmHandle() was added to tpm_deserialize_handle() in commit 5b379c0d3996152dfd6f9633b59c2e04e461e038, compiling src/lib/tpm.c fails with versions of tss2-esys before 2.4, whereas the documentation and the configure checks still specify a minimum version of 2.0.

Looking at the code, the function is only used if tpm_deserialize_handle() is called with a non-zero tpmHandle argument. At the moment, this is only true for the call in backend_fapi.c. In other words, rather than just bumping the minimum required version, we might also refactor the code to only include the function call when building with FAPI support, and leave minimum requirements for non-FAPI builds at their currently documented versions.

I'm happy to provide a patch either way, but would appreciate to hear your preference on handling this situation.

(We care about this issue because we'd like to roll out tpm2-pkcs11 on machines running Ubuntu's current LTS release 20.04, which already seems to package sufficiently recent versions for all dependencies, apart from tss2-esys 2.4. Not having to upgrade distro-provided libs would save us a lot of effort.)

[williamcroberts]

Yeah I prefer things to work with the smallest version possible, so I would take that patch to require a lower version when disabling FAPI backend.

[dkobras]

I finally got around to look into this. I'm not 100% happy with #662, and would have preferred to restrict the 2.4-only call to backend_fapi.c itself, but this not only went against current abstractions in the code, but also created a mess with the mock-up functions for the unit tests. Hence, I went with plan B that does the job without adding too much complexity. With this change, building a working tpm2-pkcs11 module on a current Ubuntu LTS with only packaged dependencies is back to a simple ./configure && make.

[williamcroberts]

@dkobras I'm assuming you'd like a release off of master for a fix release to just package?

[dkobras]

@dkobras I'm assuming you'd like a release off of master for a fix release to just package?

Thanks! Internally, we've already had a workaround in place. So we're in no hurry, and can just drop our patch once the fix is included in a regular release.