dns: refactor QueryWrap lifetime management#26253
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- Prefer RAII-style management over manual resource management. - Prefer `env->SetImmediate()` over a separate `uv_async_t`. - Perform `ares_destroy()` before possibly tearing down c-ares state. - Verify that the number of active queries is non-negative. - Let pending callbacks know when their underlying `QueryWrap` object has been destroyed. The last item has been a real bug, in that when Workers shut down during currently running DNS queries, they may run into use-after-free situations because: 1. Shutting the `Worker` down leads to the cleanup code deleting the `QueryWrap` objects first; then 2. deleting the `ChannelWrap` object (as it has been created before the `QueryWrap`s), whose destructor runs `ares_destroy()`, which in turn invokes all pending query callbacks with `ARES_ECANCELLED`, 3. which lead to use-after-free, as the callback tried to access the deleted `QueryWrap` object. The added test verifies that this is no longer an issue.
nodejs-github-bot added c++ 
addaleax added worker 
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addaleax commented Feb 28, 2019
Maybe one of @XadillaX@gireeshpunathil@joyeecheung@cjihrig could review this? |
cjihrig approved these changes Feb 28, 2019
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addaleax commented Mar 1, 2019
addaleax added the author ready 
jasnell approved these changes Mar 1, 2019
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addaleax commented Mar 1, 2019
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addaleax commented Mar 1, 2019
Landed in 018e95a |
addaleax added a commit that referenced this pull request Mar 1, 2019
- Prefer RAII-style management over manual resource management. - Prefer `env->SetImmediate()` over a separate `uv_async_t`. - Perform `ares_destroy()` before possibly tearing down c-ares state. - Verify that the number of active queries is non-negative. - Let pending callbacks know when their underlying `QueryWrap` object has been destroyed. The last item has been a real bug, in that when Workers shut down during currently running DNS queries, they may run into use-after-free situations because: 1. Shutting the `Worker` down leads to the cleanup code deleting the `QueryWrap` objects first; then 2. deleting the `ChannelWrap` object (as it has been created before the `QueryWrap`s), whose destructor runs `ares_destroy()`, which in turn invokes all pending query callbacks with `ARES_ECANCELLED`, 3. which lead to use-after-free, as the callback tried to access the deleted `QueryWrap` object. The added test verifies that this is no longer an issue. PR-URL: #26253 Reviewed-By: Colin Ihrig <[email protected]> Reviewed-By: James M Snell <[email protected]>
addaleax added a commit that referenced this pull request Mar 1, 2019
- Prefer RAII-style management over manual resource management. - Prefer `env->SetImmediate()` over a separate `uv_async_t`. - Perform `ares_destroy()` before possibly tearing down c-ares state. - Verify that the number of active queries is non-negative. - Let pending callbacks know when their underlying `QueryWrap` object has been destroyed. The last item has been a real bug, in that when Workers shut down during currently running DNS queries, they may run into use-after-free situations because: 1. Shutting the `Worker` down leads to the cleanup code deleting the `QueryWrap` objects first; then 2. deleting the `ChannelWrap` object (as it has been created before the `QueryWrap`s), whose destructor runs `ares_destroy()`, which in turn invokes all pending query callbacks with `ARES_ECANCELLED`, 3. which lead to use-after-free, as the callback tried to access the deleted `QueryWrap` object. The added test verifies that this is no longer an issue. PR-URL: #26253 Reviewed-By: Colin Ihrig <[email protected]> Reviewed-By: James M Snell <[email protected]>
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env->SetImmediate()over a separateuv_async_t.ares_destroy()before possibly tearing down c-ares state.QueryWrapobjecthas been destroyed.
The last item has been a real bug, in that when Workers shut down
during currently running DNS queries, they may run into use-after-free
situations because:
Workerdown leads to the cleanup code deletingthe
QueryWrapobjects first; thenChannelWrapobject (as it has been created beforethe
QueryWraps), whose destructor runsares_destroy(), whichin turn invokes all pending query callbacks with
ARES_ECANCELLED,deleted
QueryWrapobject.The added test verifies that this is no longer an issue.
Checklist
make -j4 test(UNIX), orvcbuild test(Windows) passes