Fix bounds check in zio_crypt_do_objset_hmacs

[tcaputi]

The current bounds check in zio_crypt_do_objset_hmacs() does not
properly handle the possible sizes of the objset_phys_t and
can therefore read outside the buffer's memory. If that memory
happened to match what the check was actually looking for, the
objset would fail to be owned, complaining that the MAC was
invalid.

Signed-off-by: Tom Caputi tcaputi@datto.com

Motivation and Context

This often broke the zpool_import_errata_003.ksh test.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commit messages are properly formatted and contain Signed-off-by.
• Change has been approved by a ZFS on Linux member.

[behlendorf]

Thanks, that nicely explains the testing failures which were observed. For good measure I've also verified the fix locally.

[codecov]

Codecov Report

Merging #7210 into master will increase coverage by 0.17%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #7210      +/-   ##
==========================================
+ Coverage   76.23%    76.4%   +0.17%     
==========================================
  Files         327      327              
  Lines      103833   103835       +2     
==========================================
+ Hits        79156    79335     +179     
+ Misses      24677    24500     -177

Flag	Coverage Δ
#kernel	75.82% <100%> (-0.5%)	⬇️
#user	65.89% <40%> (+0.49%)	⬆️

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