tls: free a stream TLS engine's SSL after its handshake pass has returned

[robobun]

Problem

• A tls.Server gets a stream that is not a net.Socket from server.emit("connection", duplex), and its ALPNCallback calls this.destroy(). The first client that offers ALPN ends the process: panic(main thread): Segmentation fault at address 0xE0 (0xB0 on 1.4.0 to 1.4.2).
• ASAN: heap-use-after-free in SSL_is_quic <- bssl::ssl_negotiate_alpn <- SSL_do_handshake <- SSLWrapper::update_handshake_state.
• The cause: ALPNCallback runs inside SSL_do_handshake. destroy() reaches SSLWrapper::deinit() (src/uws/lib.rs), which frees the SSL below that frame.

Fix

• deinit() inside a handle_traffic pass takes the SSL out of the wrapper. The pass frees it when it has unwound (Traffic::FreeRequested).
• Every other call sees a closed wrapper at once, as before. The pass stops after a handshake call that closed the wrapper.
• Correct because the handshake runs only inside a pass: write_data never drives a pending handshake.
• Verified: test/js/node/tls/node-tls-server.test.ts (2 new tests, TLS 1.3 and TLS 1.2). Also five more tls and http2 test files, listed in Notes.

Background

• SSLWrapper is the TLS engine over a JS stream. UpgradedDuplex owns one per wrapped stream. fetch and WebSocket proxy tunnels use it too.
• A pass is one handle_traffic call: handshake, reads, writes. Its traffic cell already records a re-entrant call.
• Considered the deferral in the owner's close task (tls: defer upgraded-duplex teardown to the owning context's close task #31364). The rule in the wrapper holds for every owner.

Downsides

• None found. Checked: deinit() has one caller (UpgradedDuplex::teardown) and frees at once outside a pass. Traffic stays one byte. The cost is one branch after each SSL_do_handshake call.

Notes

• Related to tls: defer upgraded-duplex teardown to the owning context's close task #31364 (the same crash, deferred in UpgradedDuplex). This PR does not replace it by itself: a maintainer decides which one lands.
• The same lines are part of the larger branch robobun/12858a05/tls-injected-sni (server names on injected connections). This PR carries them alone so that the crash fix does not wait for it.
• Before, on a debug (ASAN) build of main bc7a813 with Malloc=1: the new test ends in ERROR: AddressSanitizer: heap-use-after-free, frames SSL_is_quic (ssl_lib.cc:2994), bssl::ssl_negotiate_alpn, bssl::do_select_parameters, SSL_do_handshake, SSLWrapper::update_handshake_state, traffic_pass. On the release build 1.4.3-canary.1+367d939d9 it ends in panic(main thread): Segmentation fault at address 0xE0.
• After, on a debug build of this branch: the 2 new tests pass and the file passes (101 tests). node-tls-connect 121, node-tls-context 29, node-tls-upgrade 5, node-tls-duplex-close-throw-uaf 4, node-http2-upgrade 15.
• Node v26.3.0 answers ECONNRESET to the client that offers ALPN and serves the next client. Node also emits 'tlsClientError' there. Bun does not, on every door (listen, raw socket, Duplex). That difference is not part of this PR.
• Controls that were always alive: the raw net.Socket handed over, the server's own listen(), and a destroy() from a setImmediate.
• WindowsNamedPipe drops its wrapper behind its own WRAPPER_BUSY flag, and the proxy tunnels drop theirs with the tunnel. Drop frees at once, as before.
• Binary size of this PR alone was not measured. The larger branch, which contains these lines, measured -465 bytes of text against main 4b02e10.

---

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/node/tls/node-tls-server.test.ts

[robobun]

Status: reproduced and fixed.

• Reproduced with the new test in test/js/node/tls/node-tls-server.test.ts ("an ALPNCallback that destroys its socket over a Duplex drops that connection only"). On a debug (ASAN) build of main bc7a813 it ends in heap-use-after-free in SSL_is_quic below SSL_do_handshake. On the release build 1.4.3-canary.1+367d939d9 it ends in panic(main thread): Segmentation fault at address 0xE0.
• With this branch the two new tests pass, and so does the rest of the file.

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Walkthrough

SSLWrapper defers freeing during active traffic and stops handshake processing after closure. TLS server tests cover callback-triggered socket destruction over custom Duplex transports for TLS 1.2 and TLS 1.3.

Changes

TLS wrapper lifecycle

Layer / File(s)	Summary
Deferred freeing during traffic src/uws/lib.rs	deinit requests deferred freeing while traffic is active. handle_traffic handles reruns and frees the captured SSL after the active pass unwinds.
Closed-wrapper handling src/uws/lib.rs, test/js/node/tls/node-tls-server.test.ts	Handshake processing clears the error queue and returns when a callback closes the wrapper. Drop marks the wrapper closed and frees the SSL directly. Tests cover TLS 1.2 and TLS 1.3 connections where an ALPN callback destroys the server socket. The no-ALPN case completes the handshake with no negotiated protocol.

Suggested reviewers: jarred-sumner

Priority: ➖ Normal

Merge Risk: 🔵 Low · up to 12c33

A narrow callback-driven closure can cause an in-progress write to report success for data that was not delivered. Fix the return behavior before merging, or explicitly accept this bounded risk.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly summarizes the main change: deferring the stream TLS engine’s SSL cleanup until the handshake pass returns.
Description check	✅ Passed	The description explains the problem, the fix, and how the author verified it. It covers the required template information, although it uses different section headings.

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @src/uws/lib.rs:
- Around line 930-932: Update the public write operations in the connection
traffic flow so they reject writes when traffic is FreeRequested, even if ssl is
still present. Preserve the SSL until the active pass completes; return the
existing closed-connection result without calling SSL_write.
- Line 1407: In WebSocketProxyTunnel::start, retain a strong tunnel reference
for the full duration of SslWrapper::start by creating a RefPtr::from_this guard
before starting the wrapper; keep the guard alive until the start operation
returns.

Review comments at @test/js/node/tls/node-tls-server.test.ts:
- Line 803: Update the client tracking in the test around `connect` so both
client instances are added to the per-test resource array instead of overwriting
the first reference. Ensure `afterEach()` destroys every tracked client,
independent of either client’s error path.

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[robobun]

^{Updated 7:25 PM PT - Oct 2nd, 2026}

✅ @robobun, your commit 3de7d2193a499095e2ef0506b3f09042c470b63e passed in Build #123047! 🎉

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[claude]

Code review found no issues

No high-confidence issues detected in this change.

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⚠️ Outside diff range comments (1)

🟡 Minor · Return ConnectionClosed when the flush deinitializes the wrapper. · lib.rs:924-925

src/uws/lib.rs:924-925
🗄️ Data Integrity & Integration | 🟡 Minor | ⚡ Quick win

Return ConnectionClosed when the flush deinitializes the wrapper.

When the BIO has more than one BUFFER_SIZE chunk pending, the re-entrant handle_traffic() can invoke the write callback for the first chunk. If that callback calls deinit(), the remaining BIO output is discarded when SSL_free runs. The in-flight write_data() call still returns Ok(written), where written is the SSL_write acceptance count.

WebSocketUpgradeClient::write_pending advances its input by that count. It can therefore discard plaintext that was never delivered. Recheck the wrapper after handle_traffic() and return WriteDataError::ConnectionClosed. The initial check does not cover this already-running invocation.

Suggested fix

             self.handle_traffic();
+            if self.ssl.get().is_none() {
+                return Err(WriteDataError::ConnectionClosed);
+            }
             Ok(usize::try_from(written).expect("int cast"))

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Review comment at @src/uws/lib.rs around lines 924 - 925:
Update write_data after handle_traffic() to check whether the SSL wrapper has
been deinitialized; return WriteDataError::ConnectionClosed if so, and only
return the accepted byte count while the wrapper remains initialized.

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Outside diff comments:
Review comments at @src/uws/lib.rs:
- Around line 924-925: Update write_data after handle_traffic() to check whether
the SSL wrapper has been deinitialized; return WriteDataError::ConnectionClosed
if so, and only return the accepted byte count while the wrapper remains
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[claude]

Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.

Beyond the inline finding, I also checked whether the deferred free can outlive its wrapper: UpgradedDuplex::teardown neuters in place and the Option<SSLWrapper> is only dropped on a later tick, so the pass that frees the snapshot still has a live &self, and Drop finds ssl == None and is a no-op. I also traced the re-entrant handle_traffic flush path (a write callback calling deinit there leaves FreeRequested intact rather than overwriting it with RerunRequested) and write_data -> SSL_write, which is gated on the handshake not being pending so no JS callback can run under a BoringSSL frame from that entry point.

Extended reasoning...

The diff adds a Traffic::FreeRequested state to the unsafe-Rust SSLWrapper in /home/claude/bun/src/uws/lib.rs so that deinit() called from an ALPN callback inside SSL_do_handshake defers SSL_free until the running handle_traffic pass unwinds, plus an early return after the handshake call when the wrapper was closed, and a Drop that frees directly instead of routing through deinit. It touches TLS connection lifetime in native code, the most memory-safety-sensitive surface in the repo, but no auth, parsing, or credential handling. Every match on Traffic is exhaustive and all self.ssl.get() readers after callbacks already bail on None, and the only deinit caller keeps the wrapper alive past the pass; a human should still weigh the state-machine change given the UAF history of this file.

[claude]

🟡 nit (optional): if the deferred free regresses, maintainers see the whole 100-test file die with a segfault instead of one failing test. The new case reproduces the crash in-process; on the unfixed build the ALPNCallback destroy inside the Duplex handshake aborts the runner rather than failing the assertion at node-tls-server.test.ts:802. Fix: run the crashing scenario in a spawned fixture (bunExe()/bunEnv) and assert { exitCode, signalCode, stderr } so the regression surfaces as one red test, as the repo asks for crash fixes.

Why this was flagged

The test at test/js/node/tls/node-tls-server.test.ts:761-813 drives a TLS server over a Duplex whose ALPNCallback calls this.destroy(), the exact input that segfaulted the base build (SSL_is_quic UAF inside SSL_do_handshake). It runs in the test runner's own process. If src/uws/lib.rs:931-934 or the handle_traffic FreeRequested arm at src/uws/lib.rs:1340 regresses, the runner process itself dies, so every other test in the file is lost and the failure reads as a crashed runner, not a failed test. The repository's review guidance asks crash fixes to carry the crashing input as a spawned fixture with an asserted exit code and signal, which this test does not do. The neighbouring in-process test at line 710 has the same shape, so this is a convention nit, not a correctness defect in the fix.

Verification: The deferred-free logic in src/uws/lib.rs regresses. The new case at test/js/node/tls/node-tls-server.test.ts:761-813 runs in the test runner's own process; there is no Bun.spawn/bunExe() fixture. The crash the PR fixes is a native UAF, which on the unfixed build terminates the whole process, so the assertion at line 802 is never reached and the other ~100 tests in the file are lost.

[robobun]

Agreed. The spawned form is better, and REVIEW.md asks for it.

It is written: b64ab9a on robobun/12858a05/alpn-destroy-test-spawned, one test-only commit on top of this head.

• On a release build without the fix, each TLS version is one red test (exitCode: 139, signalCode: "SIGSEGV", the panic text in stderr), and the runner continues.
• On a debug (ASAN) build with these lines, both tests pass.

I did not push it here, because CI is green on 3de7d21 and the commit changes no source. It goes in with the next pull in this area (server names on injected connections), which carries the same test. If a maintainer prefers it in this pull, I push that commit here.

[claude]

Code review found no issues

No high-confidence issues detected in this change.

Still open from earlier reviews (1):

• Unresolved: 1 minor or pre-existing.

[robobun]

About the review note on write_data (src/uws/lib.rs:922, outside the diff): this pull does not change that result.

• On main, a write callback that calls deinit() during the flush frees the SSL at once. The loop in handle_writing stops, and write_data returns Ok(written).
• With this pull the return value is the same. Only SSL_free moves to the end of the pass.
• deinit() has one caller, UpgradedDuplex::teardown (src/runtime/socket/UpgradedDuplex.rs:661). The owner that reaches it from its own write callback has closed the connection, so no open connection loses data.

I left write_data as it is, so that this pull stays the crash fix only.

[Jarred-Sumner]

Superseded by #44618, which consolidates the open TLS pull requests. This fix and its tests are in there, either as written, rewritten smaller, or merged with the other PRs that patched the same cause (see the "By area" list in that PR). Closing in favor of it.