fix(epoll): do not touch a connection's state after a handler that ran inline on an async loop hijacked it (celeris#769) - #774
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…(AsyncHandlers, or a sync route beside an Async one)
…n inline on an async loop hijacked it
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📝 WalkthroughWalkthroughThe HTTP/1 epoll loop now skips the inline-mode reset when ChangesEpoll hijack handling
Priority: ➖ Normal Estimated code review effort: 3 (Moderate) | ~20 minutes Change: Bug fix · Severity of issue fixed: Medium Merge Risk: 🔵 Low · up to The hijack fix appears ready for normal checks, but demonstrate that the new tests catch the original failure before merging. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to The fix prevents the loop from accessing connection state after a successful hijack. It does not add a production entrypoint or change who may hijack a connection. No new security issue was established, though unusual failure and concurrent-reuse cases remain less well covered. Retained concerns Security review detailsSecurity Blast Radius
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Inline comments:
Review comments at @engine/epoll/hijack_inline_async_loop_linux_test.go:
- Line 64: Update TestInlineHijackOnAsyncLoop in
engine/epoll/hijack_inline_async_loop_linux_test.go (lines 64-64) and
TestHijackWithAsyncHandlersOnEpoll in hijack_async_handlers_epoll_linux_test.go
(lines 21-21) to add negative-control assertions: the first must fail for /hj
with the unfixed loop behavior, and the second must fail when /hj reaches the
inline path. Ensure each test detects its respective regression rather than only
asserting post-fix success.
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engine/epoll/hijack_inline_async_loop_linux_test.goengine/epoll/loop.gohijack_async_handlers_epoll_linux_test.go
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…l and io_uring, and copy the request values at Hijack (celeris#733) (#773) Bug: on epoll and io_uring, Context.Hijack let the engine return the connection's receive buffer to the pool while the hijacking handler still held request strings that view it, so the next connection's request (Authorization included) overwrote them. Change: epoll drops cs.buf before pooling the hijacked connState; io_uring releases a hijacked connState through the detached path (held until the cancelled recv's CQE, never recycled); Hijack copies the request values as Detach does (cloneRequestValues), which covers io_uring's multishot mode; a CI Unit step runs both tests with the io_uring arms required. Verification: on main + the tests (8e03dd3) epoll 11-14/20 and io_uring 10-15/20 kept strings read B's bytes, and the multishot test fails, 5/5 runs; 0 wrong and PASS 5/5 at the head; each fix reverted alone is killed 3/3 by its own arm; CI green on f3a333f (celeris#733 step: 2 tests, 4 arms, 1 io_uring arm PASS, 0 SKIP). Follow-ups: #785 (AsyncHandlers arm now that #774 is in, multishot strings read before Hijack, std copy cost, engine-side cost, doc and witness nits, CodeRabbit's backstop point to decide with #812). Fixes #733
1 participant
Fixes #769
The defect
On epoll, a handler that runs inline on an async loop and calls
Context.Hijackcrashed the process. An epoll loop is async whenConfig.AsyncHandlersis set or any route is markedAsync, and it still runs requests inline, inInlineMode, until one reaches an async route: routes that inherit theAsyncHandlersdefault start inline (#356), and so does every sync route. A handler that hijacks there takeshijackConn's inline branch, which returns the connState to the pool inside theHijackcall (h1Stateis nil afterreleaseConnState).drainReadthen clearedInlineModethroughcs.h1Statebefore it looked atErrHijacked: a nil dereference on the loop goroutine. By reading (not reproduced, see Controls): had another worker's accept already taken the released connState, the same line would have written that connection's parser state instead.Failing-first
engine/epoll/hijack_inline_async_loop_linux_test.go,TestInlineHijackOnAsyncLoop: an engine withAsyncHandlersand a handler that hijacks on/hj, in two arms: no async route (no resolver is wired, every request runs inline) and one async route beside the sync/hj. 20 hijacks, each followed by an ordinary request.hijack_async_handlers_epoll_linux_test.go,TestHijackWithAsyncHandlersOnEpoll: the user-facing shape,celeris.Config{Engine: Epoll, AsyncHandlers: true}and a route that hijacks.Test-only commit 051dace (main 698bed6 + the tests), each test 5 times, each in its own
go test -raceprocess, Docker linux/arm64,--cpus 4, memlock 8 MiB, kernel 7.0.12:TestInlineHijackOnAsyncLooppanic:and no--- FAILline, 5/5TestHijackWithAsyncHandlersOnEpollpanic:and no--- FAILline, 5/5A panic on the loop goroutine kills the test binary before
go testcan print a FAIL line, so each of the 10 processes exited 2 with onepanic:and no--- FAILline (crash/logs/ff-051dace-m8-arm64.log), every one at the reset:The fix
In
drainRead, theInlineModereset afterconn.ProcessH1is skipped whenProcessH1reportsErrHijacked: nothing touchescsafter a hijack, and the existingErrHijackedreturn a few lines below is the only way out. Every other access afterProcessH1was already behind aprocessErrcheck. In sync mode (tryInlinefalse) nothing changes, and io_uring refuses Hijack on an async worker (#539).Controls
Mutants, applied with
go test -overlay(the tree is never edited), 3 runs each ofTestInlineHijackOnAsyncLoopon the head:loop.go)cs.h1State != nil) instead of theErrHijackedcheckThe nil check avoids the crash these tests reach, but still writes a released connState whenever the pool has already handed it to another worker's accept, which set a new
h1State. That reuse needssync.Poolto move the connState across processors inside the few microseconds between the release and the reset, which no test here forces; the fix does not touchcsat all, by construction.Suites
go test -race -count=1 -v, arm64, at the head:./engine/epoll155 PASS, 0 FAIL, 3 SKIP at memlock 8 MiB and 155 PASS, 0 FAIL, 3 SKIP unlimited;.(root, CI's shape, memlock 8 MiB) 471 PASS, 0 FAIL, 4 SKIP. The skips are gated by the environment and predate this branch (GOTEST_BACKPRESSURE,net.ipv4.tcp_synack_retries=0twice,CELERIS_592_COST, andTestAdaptiveSettledRouteRetime592's three io_uring subtests, which need memlock for two io_uring workers). No race report.linux/amd64 (qemu emulation, a compile and a quick run without
-race): both tests PASS.Host:
GOOS=linuxbuild of the module,go test -cof both packages,go vetand golangci-lint (the repo's config), for amd64 and arm64: clean.Cost
Argued, not measured: one
errors.IsonprocessErr, only on an async loop's inline requests, and only afterProcessH1has returned. With a nilprocessErr,errors.Isreturns at its first comparison. On an async route the first inline attempt returnsErrAsyncDispatch, and that request pays a fullerrors.Iscall (a comparison and anUnwrapprobe of a sentinel fromerrors.New).Follow-ups
The review's minor findings and nits are in #786: a pre-existing epoll defect found while reading
drainRead(a first segment shorter than protocol detection needs is overwritten by the next read), a test that forces the connState-reuse face so the nil-check mutant fails, a witness that/hjran inline, and this Cost wording.Found by
The first version of #733's regression test (#773), whose epoll arm with
AsyncHandlerscrashed on main 5 of 5 runs.Evidence
Every number above comes from a script under the maintainer's evidence tree,
evidence/lanes-20260927/EPOLL-HIJACK/crash/and the lane's queue scripts, with logs incrash/logs/.