The following testcase crashes on mozilla-central revision d10c97627b51 (build with --enable-posix-nspr-emulation --enable-valgrind --enable-gczeal --disable-tests --enable-stdcxx-compat --disable-profiling --enable-debug --enable-optimize, run with --fuzzing-safe): function evalModuleAndCheck(source, expected) { let m = parseModule(source); getModuleEnvironmentValue(m, "r").toString() } evalModuleAndCheck("export let r = y; y = 4;"); Backtrace: received signal SIGSEGV, Segmentation fault. 0x000000000052bfa8 in js::GetProperty (cx=0x7ffff6924000, v=..., name=..., vp=...) at js/src/vm/Interpreter.cpp:4392 #0 0x000000000052bfa8 in js::GetProperty (cx=0x7ffff6924000, v=..., name=..., vp=...) at js/src/vm/Interpreter.cpp:4392 #1 0x0000000000531103 in GetPropertyOperation (vp=..., lval=..., pc=<optimized out>, script=..., fp=<optimized out>, cx=<optimized out>) at js/src/vm/Interpreter.cpp:192 #2 Interpret (cx=0x7ffff6924000, state=...) at js/src/vm/Interpreter.cpp:2784 #3 0x000000000053da33 in js::RunScript (cx=0x7ffff6924000, state=...) at js/src/vm/Interpreter.cpp:409 [...] #12 main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at js/src/shell/js.cpp:8592 rax 0x0 0 rbx 0x7ffff6924000 140737330167808 rcx 0x7ffff6c28a2d 140737333332525 rdx 0x0 0 rsi 0x7ffff6ef7770 140737336276848 rdi 0x7ffff6ef6540 140737336272192 rbp 0x7fffffffcc50 140737488342096 rsp 0x7fffffffcbb0 140737488341936 r8 0x7ffff6ef7770 140737336276848 r9 0x7ffff7fe4740 140737354024768 r10 0x58 88 r11 0x7ffff6b9f750 140737332770640 r12 0x7fffffffd0a0 140737488343200 r13 0x7ffff4280140 140737289650496 r14 0x7fffffffd0e0 140737488343264 r15 0x7ffff6924020 140737330167840 rip 0x52bfa8 <js::GetProperty(JSContext*, JS::Handle<JS::Value>, JS::Handle<js::PropertyName*>, JS::MutableHandle<JS::Value>)+776> => 0x52bfa8 <js::GetProperty(JSContext*, JS::Handle<JS::Value>, JS::Handle<js::PropertyName*>, JS::MutableHandle<JS::Value>)+776>: movl $0x0,0x0 0x52bfb3 <js::GetProperty(JSContext*, JS::Handle<JS::Value>, JS::Handle<js::PropertyName*>, JS::MutableHandle<JS::Value>)+787>: ud2 Marking s-s because both assertions can indicate security-sensitive type confusions.

anba could this be from your module changes? Just a wild guess, JSBugMon bisection results would be good :)

(In reply to Jan de Mooij [:jandem] from comment #1) > anba could this be from your module changes? > > Just a wild guess, JSBugMon bisection results would be good :) No, I've recently only touched ModuleNamespaceObject, but didn't tinker with ModuleEnvironmentObject. GetModuleEnvironmentValue is probably just missing an uninitialized-lexical check. With the following patch applied, the test case no longer asserts: diff --git a/js/src/builtin/TestingFunctions.cpp b/js/src/builtin/TestingFunctions.cpp --- a/js/src/builtin/TestingFunctions.cpp +++ b/js/src/builtin/TestingFunctions.cpp @@ -3974,17 +3974,23 @@ GetModuleEnvironmentValue(JSContext* cx, } RootedModuleEnvironmentObject env(cx, GetModuleEnvironment(cx, args[0])); RootedString name(cx, args[1].toString()); RootedId id(cx); if (!JS_StringToId(cx, name, &id)) return false; - return GetProperty(cx, env, env, id, args.rval()); + if (!GetProperty(cx, env, env, id, args.rval())) + return false; + if (args.rval().isMagic(JS_UNINITIALIZED_LEXICAL)) { + ReportRuntimeLexicalError(cx, JSMSG_UNINITIALIZED_LEXICAL, id); + return false; + } + return true; }

autoBisect shows this is probably related to the following changeset: The first bad revision is: changeset: https://hg.mozilla.org/mozilla-central/rev/1ac68e528d12 user: Jon Coppeard date: Thu Oct 08 10:49:49 2015 +0100 summary: Bug 1209107 - Only expose module environment object through testing functions r=shu Jon, is bug 1209107 a likely regressor?

André is correct. This is just a problem with the getModuleEnvironmentValue() testing function, not a security issue.

Pushed by jcoppeard@mozilla.com: https://hg.mozilla.org/integration/mozilla-inbound/rev/8ad07e576ee7 Check for uninitialised lexicals in getModuleEnvironmentValue() r=arai