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node:net: refuse connect() through a handle that shares its transport - #46843
Fixes a use-after-free when connect() is called on a net.Socket that was handed to tls.connect({ socket }). The call now fails with EISCONN and dials nothing.
tls.connect({ socket }) upgrades in place: the TLS socket's handle and the raw handle left in the plain socket's _handle share one native socket, whose ext slot names the TLS handle. A connect() with TLS options reused the raw handle, and detach_for_reconnect emptied that slot and closed the socket. The TLS handle never heard of the close and kept a pointer the loop freed at the end of the turn. Dialing through the TLS handle left the raw one dangling the same way. Both segfault a release build.
connect_inner now asks the handle first (can_reconnect). Either half of a pair, a TLS engine over a Duplex and a named pipe are refused through the path a synchronous connect failure already takes, so net.ts is unchanged.
Without TLS options the same call dialed a connection _handle never pointed to, and the process never exited. It is refused too.
Differs from Node on Linux: there the first redundant connect(2) answers 0, so 'connect' fires again and the session lives.
Left as on main: for a host with several addresses, node:net takes the EISCONN as one failed attempt. Its next attempt closes the raw handle and is cancelled (ECANCELED), so both sockets close, the TLS one with ECONNRESET and the plain one with no 'error'. The Windows pipe arms still reuse a live TCP handle without detaching it.
bun bd test test/js/node/net/socket-reconnect-live.test.ts passes; the two new tests fail with USE_SYSTEM_BUN=1 and on a debug+ASAN build of main (heap-use-after-free in us_socket_get_native_handle).
400 vendored test-net-*/test-tls-*/test-https-* tests and 49 net/tls suite files, compared with main: no new failure.
cargo clippy -p bun_runtime is clean. The Windows changes are type-checked only.
`tls.connect({ socket })` on a connected `net.Socket` upgrades in place:
the TLS socket's handle and the raw handle left in the plain socket's
`_handle` share one native socket, whose ext slot names the TLS handle.
A `connect()` with TLS options on the plain socket passed the raw handle
to `doConnect` as the previous socket. `detach_for_reconnect` emptied the
shared slot and closed the socket, so the TLS handle never heard of the
close and kept a pointer to memory the loop freed at the end of the turn.
It also gave back a reference that belongs to the TLS handle's `twin`.
Dialing through the TLS handle left the raw handle dangling the same way.
`connect_inner` now asks the handle first (`can_reconnect`). Either half
of an `upgradeTLS` pair, a TLS engine over a `Duplex` and a named pipe
are turned away: nothing is dialed and the attempt fails with EISCONN
through the path a synchronous connect failure already takes, so node:net
destroys the socket with `connect EISCONN`. The pair is closed by that
destroy, and both sockets are told.
Without TLS options the same call used to dial a second connection on a
wrapper that `_handle` never pointed to, which kept the process alive
after everything was destroyed. It is refused as well.
Reconnect attempts involving sockets that cannot be reused now report EISCONN without starting another connection. The changes add reconnect eligibility checks and tests for wrapped sockets and shared transport handles.
Changes
Socket Reconnect Refusal
Layer / File(s)
Summary
Reconnect eligibility and error codes src/runtime/socket/socket_body.rs
can_reconnect rejects TLS-bypass sockets, sockets with a twin, and unsupported states. Connect error handling preserves EISCONN.
The tests check error events and server accept counts for wrapped sockets and shared transport handles.
Suggested reviewers: jarred-sumner
Priority: Normal
Merge Risk: Moderate · up to 6dc97
The reconnect test can pass despite an extra connection in the scenario it is meant to protect. Match accepted connections to intended dials before merging.
Pre-merge checks: 4
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Explanation
Title check
The title clearly and concisely describes the main change: refusing connect() through a handle that shares its transport.
Description check
The description includes both required sections. It explains the fix, affected scenarios, known limitations, verification steps, and test results.
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Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.
Beyond the inline findings, I also checked the new refused early return in connect_finish for refcount balance — it repeats the existing synchronous do_connect failure arm exactly (handle_connect_error, then the deref that balances the unconditional ref_(), then handled?), so no ref is leaked or double-released on that path. The new assert! in detach_for_reconnect is reached only through the Previous::Reuse arm, which connect_inner takes only after can_reconnect() returned true for that same handle.
Extended reasoning...
The change touches src/runtime/socket/Listener.rs and src/runtime/socket/socket_body.rs (node:net connect() on an already-connected socket whose native handle is shared with a TLS wrapper) plus a new subprocess test; it is a memory-safety fix in unsafe socket lifecycle code with five confirmed inline findings, so a human look is already signalled by those. The ruled-out note records the refused-path refcount audit and the assert reachability check.
On macOS x64 one scenario reported `accepted: 0` on its first attempt:
the refusal destroys the sockets within a few loop turns, and a
connection that is reset before the server gets to accept it is never
handed over there.
Each scenario now ends with one more connection. Connections are accepted
in the order they were made, so once that one is accepted any dial made
before it has been too, and the test asserts that no more were accepted
than the scenario meant to make.
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Actionable comments posted: 1
🪄 Fix comments: Fix CodeRabbit comments on this PR
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only still-valid issues, skip the rest with a brief reason, keep changes
minimal, and validate.
Inline comments:
Review comments at @test/js/node/net/socket-reconnect-live.test.ts:
- Line 185: Update the `otherDials` calculation to identify accepted connections
by comparing their ports with the intended dial ports, rather than subtracting
the number of intended dials from the accepted count. Count accepted connections
that do not match an intended dial so a replacement reconnect is still detected.
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test/js/node/net/socket-reconnect-live.test.ts
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What does this PR do?
Fixes a use-after-free when
connect()is called on anet.Socketthat was handed totls.connect({ socket }). The call now fails withEISCONNand dials nothing.tls.connect({ socket })upgrades in place: the TLS socket's handle and the raw handle left in the plain socket's_handleshare one native socket, whose ext slot names the TLS handle. Aconnect()with TLS options reused the raw handle, anddetach_for_reconnectemptied that slot and closed the socket. The TLS handle never heard of the close and kept a pointer the loop freed at the end of the turn. Dialing through the TLS handle left the raw one dangling the same way. Both segfault a release build.connect_innernow asks the handle first (can_reconnect). Either half of a pair, a TLS engine over aDuplexand a named pipe are refused through the path a synchronous connect failure already takes, sonet.tsis unchanged.Without TLS options the same call dialed a connection
_handlenever pointed to, and the process never exited. It is refused too.Differs from Node on Linux: there the first redundant
connect(2)answers 0, so'connect'fires again and the session lives.Left as on main: for a host with several addresses, node:net takes the
EISCONNas one failed attempt. Its next attempt closes the raw handle and is cancelled (ECANCELED), so both sockets close, the TLS one withECONNRESETand the plain one with no'error'. The Windows pipe arms still reuse a live TCP handle without detaching it.May conflict with #45346 and #45519.
How did you verify your code works?
bun bd test test/js/node/net/socket-reconnect-live.test.tspasses; the two new tests fail withUSE_SYSTEM_BUN=1and on a debug+ASAN build of main (heap-use-after-freeinus_socket_get_native_handle).test-net-*/test-tls-*/test-https-*tests and 49 net/tls suite files, compared with main: no new failure.cargo clippy -p bun_runtimeis clean. The Windows changes are type-checked only.Generated by Claude Code