Nullify the hypertable cache pointer on invalidation

[alexeyklyukin]

Failure to do this results in the possible use after free if hypertable_cache_create fails due to out of memory.

Observed a segfault on the running instance under low memory condition (schema obfuscated):

[1034109]: [69d02db8.fc77d-15] [XX000] ERROR:  cache "(null)" is not initialized

[1034109]: [69d02db8.fc77d-16]  [XX000] STATEMENT:  INSERT INTO sample_table (a_id, timestamp, metric, b_text, c_text, d_text, created, updated, e_bool) VALUES ($1, $2, $3, $4, $5, $6, NOW(), NOW(), false) ON CONFLICT (a_id, timestamp, metric, b_text) DO NOTHING
[891]: [69c81ac3.37b-1174] 0 @,app= [00000] LOG:  server process (PID 1034109) was terminated by signal 11: Segmentation fault
[891]: [69c81ac3.37b-1175] 0 @,app= [00000] DETAIL:  Failed process was running: INSERT INTO sample_table (a_id, timestamp, metric, b_text, c_text, d_text, created, updated, e_bool) VALUES ($1, $2, $3, $4, $5, $6, NOW(), NOW(), false) ON CONFLICT (a_id, timestamp, metric, b_text) DO NOTHING

Disable-check: force-changelog-file

[github-actions]

@Poroma-Banerjee, @svenklemm: please review this pull request.

Powered by pull-review

[akuzm]

Discussed offline that it makes more sense ts_cache_invalidate, because the core problem that it is supposed to release our pointer to the cache, but it doesn't actually nullify the pointer.

[akuzm]

I could construct a test but it needed an error injection point: #9644

[svenklemm]

This seems similar to #9610 so might already be fixed in main

[alexeyklyukin]

@svenklemm I think #9610 doesn't have path where cache is pinned correctly, i.e. for a global hyper table cache pointer, the NULL is assigned only when the cache is destroyed; however, if the old cache is pinned, but the global cache pointer is not assigned due to out of memory, it keeps pointing to the soon-to-be-released (at rollback) struct, causing SIGSEGV on access.

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/cache.c	33.33%	1 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!