Clear exceptions thrown by property lookups during inspect's property walk - #38463
Clear exceptions thrown by property lookups during inspect's property walk#38463robobun wants to merge 2 commits into
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… walk forEachPropertyImpl only cleared the exception from getPropertySlot when the lookup reported the property as found. A Proxy get trap or a lazy static property builder that throws makes getPropertySlot return false, so the loop moved on to the next property with that exception still pending. Every following lookup then failed as well (release builds drop the rest of the object's properties from the output), the next lazy builder tripped the exception scope assertion in debug builds, and a Proxy getPrototypeOf step returned an empty value that was dereferenced. Clear the exception before checking the lookup result, and stop the prototype walk when getPrototype itself throws instead of calling getObject() on an empty JSValue. The debug-only reportUncaughtExceptionAtEventLoop calls in the Bun.sql builders ran the uncaught exception handler while the module load error was still pending on the VM, which hits JSC assertions in the property get inside that handler. The error is propagated to the caller right after, so the extra report is not needed.
WalkthroughChangesSQL exception cleanup
Inspection exception handling
Suggested reviewers: 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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In `@test/js/bun/util/inspect.test.js`:
- Around line 965-971: Update both Promise.all calls in
test/js/bun/util/inspect.test.js at lines 965-971 and 999-1005 to await
proc.stderr.text() concurrently with proc.stdout.text() and proc.exited,
ensuring every piped subprocess stream is drained before completion.
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📒 Files selected for processing (3)
src/jsc/bindings/BunObject.cppsrc/jsc/bindings/bindings.cpptest/js/bun/util/inspect.test.js
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- src/jsc/bindings/BunObject.cpp
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Pushed b5b9f06: both new tests now read the child's stderr alongside stdout and the exit code (and assert it is empty), so a noisy child can't block on the pipe. Re-checked that both tests still fail on the unfixed build and pass on the debug build; the rest of inspect.test.js passes too. |
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This PR may be a duplicate of:
Also in the same family with partial overlap: #37213, #37202, #37160, #37001. 🤖 Generated with Claude Code |
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Confirmed: #37428 carries the same source change as this PR (the same two hunks in forEachPropertyImpl and the same removal of the debug-only report calls in the Bun.sql builders), and its CI is green. #29642, #30099, #37175 and #37256 fix the same crash as well, and the first two also cover the matching getPrototype() pattern in napi_get_all_property_names. Closing this one as a duplicate in favor of #37428. |
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| stdout: "pipe", | ||
| stderr: "pipe", | ||
| }); | ||
| const [stdout, exitCode] = await Promise.all([proc.stdout.text(), proc.exited]); |
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🟡 Both new subprocess tests set stderr: "pipe" but never drain it — Promise.all only awaits proc.stdout.text() and proc.exited. REVIEW.md's "Subprocess tests: drain pipes concurrently" rule requires reading every piped stream, and the neighboring subprocess tests in this file all do so. Add proc.stderr.text() to the Promise.all (here and at line 1005), or drop stderr: "pipe" if stderr is intentionally ignored.
Extended reasoning...
What the issue is
Both tests added in the new describe("property lookup throws while formatting an object") block spawn a child with stderr: "pipe", but the await line is:
const [stdout, exitCode] = await Promise.all([proc.stdout.text(), proc.exited]);proc.stderr is piped but never read. This appears at both inspect.test.js:971 (the Proxy-traps test) and inspect.test.js:1005 (the Bun.inspect(Bun) test).
Why this violates the repo's review rules
REVIEW.md states this explicitly under Tests reviewers reject:
Subprocess tests: drain pipes concurrently.
Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited])— an unread pipe fills the ~64KB OS buffer and deadlocks the child. assert a combined{ stdout, stderr, exitCode }object.
It is also inconsistent with the file's own conventions: the two neighboring subprocess tests in this file — the huge-sparse-array test (~line 446) and the ASAN mutated-object test (~line 900) — both do Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]) and assert on stderr.
Step-by-step: how the pattern can bite
- The second test spawns a child that runs
Bun.inspect(Bun)withREDIS_URLset to an invalid URL. Bun.inspect(Bun)reifies every lazy property builder on the Bun object ($,sql,postgres,SQL,s3,redis,stdin/stdout/stderr, …). The redis builder is deliberately made to throw.- The child's stderr fd is a pipe backed by an OS buffer of roughly 64 KB.
- If any of these builders — or a future one — writes enough to stderr (debug logging, error dumps, warnings), the child's next
write(2)on stderr blocks because nothing in the parent is reading the pipe. - The child never exits,
proc.exitednever resolves, and theit.concurrenttest hangs until the runner times it out.
In practice, an actual deadlock is unlikely today: bunEnv sets BUN_DEBUG_QUIET_LOGS=1, the redis URL error is short, and the fix in this PR clears exceptions rather than printing them. So this is filed as a nit rather than a blocker. But piping-without-reading is precisely the pattern the repo rule forbids, and the second test's fixture (Bun.inspect(Bun)) is exactly the kind of thing whose stderr volume changes as new lazy builders are added to Bun.
Secondary cost: lost diagnostics
Beyond the deadlock hazard, not draining stderr means that when this test does fail (e.g. the child crashes on a regression), the failure output shows only an empty stdout and a nonzero exit code — the child's stderr, which would contain the actual crash report, is discarded. Asserting a combined { stdout, stderr, exitCode } object (as REVIEW.md recommends and as the neighboring tests do) surfaces that information automatically.
Fix
Change both call sites to:
const [stdout, stderr, exitCode] = await Promise.all([
proc.stdout.text(),
proc.stderr.text(),
proc.exited,
]);and either assert on stderr or include it in the asserted object. Alternatively, if stderr content is intentionally irrelevant, drop stderr: "pipe" from the spawn options entirely so it inherits and is never buffered.
| JSValue prototype = iterating->getPrototype(globalObject); | ||
| // Ignore exceptions from Proxy "getPrototypeOf" traps. | ||
| CLEAR_IF_EXCEPTION(scope); | ||
| if (!prototype) [[unlikely]] | ||
| break; | ||
| iterating = prototype.getObject(); |
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🟣 Pre-existing, not blocking: the same getPrototype(globalObject).getObject() null-deref this hunk fixes has one other site in the tree — src/jsc/bindings/napi.cpp:2080, in napi_get_all_property_names's descriptor-filter loop. A throwing Proxy getOwnPropertyDescriptor/getPrototypeOf trap there produces the same empty-JSValue → .getObject() segfault; worth the same split-and-guard treatment as a follow-up.
Extended reasoning...
What & where
REVIEW.md's "Fix the whole class in the same PR — grep for every sibling site sharing the pattern" rule prompts a grep for the exact chained call this PR's second bindings.cpp hunk fixes. getPrototype(globalObject).getObject() has exactly one other occurrence in src/: src/jsc/bindings/napi.cpp:2080, inside napi_get_all_property_names:
JSObject* owner = object;
if (key_mode == napi_key_include_prototypes) {
// Climb up the prototype chain to find inherited properties
while (!owner->getOwnPropertyDescriptor(globalObject, propKey, desc)) {
JSObject* proto = owner->getPrototype(globalObject).getObject();
if (!proto) {
break;
}
owner = proto;
}
}There is no exception check between line 2079 (getOwnPropertyDescriptor) and line 2085, and no guard on getPrototype's return value before .getObject() is called on it.
Code path that triggers it
napi_get_all_property_names is called by native N-API modules. The loop at 2077–2085 is reached when:
key_mode == napi_key_include_prototypes, andkey_filterincludes any ofnapi_key_enumerable | napi_key_writable | napi_key_configurable(thefilter_by_any_descriptorgate at line 2069).
owner starts at the user-supplied object (from toJS(objectNapi)) and climbs its prototype chain, so a Proxy anywhere in that chain is reachable from JS.
Why the existing code doesn't prevent it
The if (!proto) break; check at line 2081 never runs when getPrototype returns an empty JSValue. As the PR description establishes for the bindings.cpp case: an empty JSValue encodes as 0, so isCell() returns true (0 & NotCellMask == 0), asCell() returns nullptr, and ->isObject() reads m_type at offset 5 from nullptr — segfault at address 0x5. The null check is dead code on the throwing path.
There is also no RETURN_IF_EXCEPTION / NAPI_RETURN_IF_EXCEPTION between getOwnPropertyDescriptor (which invokes the Proxy getOwnPropertyDescriptor trap) and getPrototype (which invokes the Proxy getPrototypeOf trap).
Step-by-step proof
Concrete example — a native addon calls:
napi_get_all_property_names(env, obj, napi_key_include_prototypes,
napi_key_enumerable, napi_key_numbers_to_strings, &result);where obj is:
Object.create(new Proxy({ a: 1 }, {
getOwnPropertyDescriptor() { throw new Error("trap"); }
}))collectInheritedPropertyKeys(line 2060) enumerates"a"from the proxy target viagetPropertyNames.- The filter loop enters with
propKey = "a",owner = obj(the plain child). owner->getOwnPropertyDescriptor(...)on the child returns false (no own"a"), no exception yet.owner->getPrototype(globalObject)returns the Proxy;.getObject()succeeds;owner = proxy.- Loop iterates:
owner->getOwnPropertyDescriptor(...)now invokes the Proxy trap, which throws.ProxyObject::performGetOwnPropertyDescriptorreturns false viaRETURN_IF_EXCEPTION, leaving the exception pending. - Loop body runs:
owner->getPrototype(globalObject)on the Proxy entersProxyObject::getPrototype, whose throw scope observes the pending exception and returns{}(empty JSValue). .getObject()on the empty JSValue:isCell()→ true,asCell()→ nullptr,->isObject()reads offset 5 from nullptr → SIGSEGV at 0x5.
A second variant: a stateful getPrototypeOf trap that succeeds during collectInheritedPropertyKeys' getPropertyNames walk (line 2007) but throws on the per-key descriptor climb hits step 6 directly — getPrototype returns {} and .getObject() segfaults the same way.
Impact
Segfault (crash) of the Bun process when a native N-API module calls napi_get_all_property_names with napi_key_include_prototypes + a descriptor filter on an object whose prototype chain contains a Proxy with a throwing getOwnPropertyDescriptor or getPrototypeOf trap. The surface is much narrower than Bun.inspect (requires a native addon using this specific N-API call with these specific flags), which is why it's flagged as a follow-up rather than a blocker.
How to fix
Same treatment as this PR applies at bindings.cpp:5684–5689: split the chained call, check for an exception after getOwnPropertyDescriptor and after getPrototype, and bail (NAPI_RETURN_IF_EXCEPTION or break out of the filter loop) when either is set or when the returned JSValue is empty. The owner->getOwnPropertyDescriptor at line 2087 (the napi_key_own_only branch) also lacks an exception check and should get one in the same follow-up.
Why this is pre_existing
The PR does not touch napi.cpp, does not add callers to napi_get_all_property_names, and lives in a separate subsystem (N-API vs. Bun.inspect). This code has been shaped this way since before the PR. It is the exact bug class the PR fixes and the only other site with the pattern, so REVIEW.md's whole-class rule makes it worth mentioning — but it should not block merging this fix.
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What does this PR do?
Found by fuzzing. The fuzzer's script replaced the global
Symbolwith a number and then callednew CompressionStream(globalThis). The error message for the badformatargument inspectsglobalThis, which walks theBunobject, andBun.$is a lazy static property whose builder runsshell.ts, which callsSymbol("cwd")and throws. In debug builds the process died withRoot cause is in
JSC__JSValue__forEachPropertyImpl(bindings.cpp), the property walk used byBun.inspect/console.log:When the lookup throws (a Proxy
gettrap, or a lazy static property builder;setUpStaticFunctionSlotreports the property as not found in that case),getPropertySlotreturns false and the loop continued with the exception still pending on the VM. Consequences:setUpStaticFunctionSlotchecks for a pending exception after reifying. In release builds this silently drops the rest of the object from the output:REDIS_URL=http://x bun -e 'console.log(Bun)'prints nothing afterredis(secrets,write,zstd*are all missing).getPrototypecall at the end of the loop returns an emptyJSValuebecause of the pending exception, and.getObject()on it dereferences null. Release builds segfault at address 0x5 onBun.inspect(Object.create(new Proxy({a: 1, b: 2}, { get(t, k) { if (k === "a") throw 1; return t[k]; } }))).The fix is to clear the exception before looking at the result of
getPropertySlot, which is whatJSC__JSValue__forEachPropertyOrderedalready does. The second hunk in the same function handlesgetPrototypeitself throwing (a ProxygetPrototypeOftrap on an object in the prototype chain), which segfaulted the same way independently of the first bug; the walk now stops there, matching how the fast path in this function already treats that trap.The
BunObject.cpphunk removes the debug-onlyreportUncaughtExceptionAtEventLoopcalls in the twoBun.sqlbuilders. They ran the uncaught exception handler while the module load error was still pending on the VM, and theprocess._fatalExceptionlookup inside that handler then hits JSC'sstoredPrototype/JSObject::getassertions. With theSymboltampering above,Bun.inspect(Bun)reaches these builders right after the first fix, so debug builds still crashed on the fuzzer's script without this. The error is propagated to the caller on the next line anyway, soBun.sqlnow just throws the load error in debug builds like it does in release.How did you verify your code works?
Two tests added to
test/js/bun/util/inspect.test.js, both running the scenario in a child process since a regression is a crash rather than a thrown error:Proxy traps in the prototype chain: thegettrap andgetPrototypeOftrap cases above. On the unfixed build the child segfaults and prints nothing.lazy property of the Bun object:REDIS_URLset to an invalid URL so theBun.redisbuilder throws, then checks which keys ofObject.keys(Bun)are missing fromBun.inspect(Bun). Unfixed release prints["redis","secrets","write","zstdCompressSync","zstdDecompressSync","zstdCompress","zstdDecompress"], unfixed debug crashes, fixed prints["redis"].Both fail with
USE_SYSTEM_BUN=1 bun testand pass withbun bd test. The rest ofinspect.test.js,BunObject.test.ts,bun-inspect.test.ts,custom-inspect.test.jsandconsole-table.test.tspass on the debug build. The original fuzzer script (evaluated in the global scope the way the REPRL harness runs it) crashes the unfixed debug build with the assertion above and runs to completion on the fixed one, also withBUN_JSC_validateExceptionChecks=1.no test proof · iteration 0 · Platform-specific test(s) that do not run on this machine. Deferring to CI, which covers all platforms: test/js/bun/util/inspect.test.js