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LegalizeJSInterface: heap-use-after-free in Fixer::visitCall when a function named $legalfunc$<import> already exists

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Valutazione

Difficoltà
3/5
Tempo stimato
1-2 giorni
Idoneità per principianti
62/100
Tipo di issue
Bug
Chiarezza
Specificata chiaramente
Stato di attività
Attiva
Stack tecnologico
cpp, wasm
Ambito
compilers

Direzione di ricerca

The crash involves makeLegalStubForCalledImport and Fixer::visitCall in src/passes/LegalizeJSInterface.cpp. Read how the stub's unique_ptr is handled when a function with the same name already exists, and how illegalImportsToLegal keeps its pointer. Build with ASan and run the three-line reproducer from the issue with --legalize-js-interface. Done when that run is clean and the call is legalized correctly even when a user function named $legalfunc$imp exists.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

--legalize-js-interface reads freed memory, and the release build segfaults, when the module already has a function whose name is the one the pass picks for its stub ($legalfunc$imp here).

(module
 (import "env" "imp" (func $imp (param i64) (result i32)))
 (func $legalfunc$imp (param i64) (result i32) (i32.const 7))
 (func $f (result i32) (call $imp (i64.const 1)))
)

wasm-opt input.wat --legalize-js-interface -o /dev/null

ASan build (with BINARYEN_PASS_DEBUG=1):

==192075==ERROR: AddressSanitizer: heap-use-after-free on address 0x516000000f80 at pc 0x557ea312a1f1 bp 0x7fa01da45390 sp 0x7fa01da45380
READ of size 8 at 0x516000000f80 thread T2
    #0 0x557ea312a1f0 in visitCall src/passes/LegalizeJSInterface.cpp:138
    #1 0x557ea312a1f0 in doVisitCall src/wasm-delegations.def:23
    #2 0x557ea30b5738 in walk src/wasm-traversal.h:318
freed by thread T0 here:
    #3 0x557ea311338d in std::unique_ptr<wasm::Function, std::default_delete<wasm::Function> >::~unique_ptr() /usr/include/c++/11/bits/unique_ptr.h:361
    #4 0x557ea311338d in makeLegalStubForCalledImport src/passes/LegalizeJSInterface.cpp:319

I expected the pass to legalize the call normally. The module is valid (wasm-opt input.wat -o /dev/null exits 0) and function names are free-form, so a user function called $legalfunc$imp should not break the pass.

Found at commit 93d6e9de7e1d99be22a49b8952426906a65df397 and still reproduces at 207bbaec4b30 (ASan build). A normal release build crashes with SIGSEGV and prints nothing. -all is not needed.

Looks like makeLegalStubForCalledImport in src/passes/LegalizeJSInterface.cpp builds the stub in a unique_ptr, keeps stub.get(), and only adds the stub to the module if no function with that name exists. Here one exists, so the stub is freed on return, and the dangling pointer stored in illegalImportsToLegal is later read by Fixer::visitCall.

Found with an LLM-based testing tool; I used Claude to reduce it and look for the cause.

Lingua principale
WebAssembly
Stelle
8.7k
Fork
895
Merge medio
1g 23h
PR unite (30g)
105

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