fix: initialize config_gen_ectx on allocation to prevent use-after-poison#546
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fix: initialize config_gen_ectx on allocation to prevent use-after-poison#546
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…ison Long-story-short: there was random dataplane crash with ASAN build. Now it's gone. Explanation requires detailing about cp/dp config exchanges. The `cp_config_gen_create` and `cp_config_gen_create_from` allocate `cp_config_gen` via `memory_balloc`, which does not(!) zero memory. When the block allocator returns a recycled block, the `config_gen_ectx` field contains stale data from its previous owner. The dataplane worker reads this field via `ADDR_OF(&cp_config_gen->config_gen_ectx)`, which computes a relative pointer: `stored_offset + &field`. With stale (non-zero) content, this resolves to a wild pointer into freed (ASAN-poisoned) memory, causing a `use-after-poison` crash in `worker_loop_round`. The fix explicitly sets `config_gen_ectx = NULL` right after allocation in both creation paths, so `ADDR_OF` correctly returns NULL before `config_gen_ectx_create` has a chance to set the real value. The fun part: the mock previously contained a workaround. This is no longer needed since the fix is now inside `cp_config_gen_create` itself. A regression test (`config_gen_test`) reproduces the bug by polluting the allocator pool with garbage before calling `cp_config_gen_create`. Without the fix, the stale offset resolves to a wild pointer and the volatile read triggers UBSAN/ASAN. With the fix, `ADDR_OF` returns NULL and the access is skipped.
sakateka
approved these changes
Mar 18, 2026
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Long-story-short: there was random dataplane crash with ASAN build. Now it's gone.
Explanation requires detailing about cp/dp config exchanges.
The
cp_config_gen_createandcp_config_gen_create_fromallocatecp_config_genviamemory_balloc, which does not(!) zero memory. When the block allocator returns a recycled block, theconfig_gen_ectxfield contains stale data from its previous owner.The dataplane worker reads this field via
ADDR_OF(&cp_config_gen->config_gen_ectx), which computes a relative pointer:stored_offset + &field. With stale (non-zero) content, this resolves to a wild pointer into freed (ASAN-poisoned) memory, causing ause-after-poisoncrash inworker_loop_round.The fix explicitly sets
config_gen_ectx = NULLright after allocation in both creation paths, soADDR_OFcorrectly returns NULL beforeconfig_gen_ectx_createhas a chance to set the real value.The fun part: the mock previously contained a workaround. This is no longer needed since the fix is now inside
cp_config_gen_createitself.A regression test (
config_gen_test) reproduces the bug by polluting the allocator pool with garbage before callingcp_config_gen_create. Without the fix, the stale offset resolves to a wild pointer and the volatile read triggers UBSAN/ASAN. With the fix,ADDR_OFreturns NULL and the access is skipped.