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Fix UAF of a suspended coroutine referenced only via a closure #1569
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,35 @@ | ||
| import * as std from "qjs:std"; | ||
| import { assert } from "./assert.js"; | ||
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| // Regression test: a suspended coroutine reachable only through a closure that | ||
| // captured one of its locals must not be collected while it is still live. | ||
| // | ||
| // A closure capturing a coroutine local holds an *open* var_ref into the | ||
| // coroutine's frame. Open var_refs are not GC objects and are not marked by | ||
| // the closure, so the edge closure -> open var_ref -> value is invisible to | ||
| // the cycle collector. An ordinary function's frame is a live C-stack root, but | ||
| // a suspended coroutine's frame is a heap GC object, so if the only thing | ||
| // keeping it reachable is such an escaped closure, the whole still-live | ||
| // coroutine used to be collected -- and resuming it, or running the closure, | ||
| // then touched freed memory. | ||
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| // | ||
| // The async function below suspends at `await d.promise`; that promise is never | ||
| // resolved, so nothing keeps the coroutine reachable except `leaked`'s capture | ||
| // of the frame local `d`. Forcing a GC while it is suspended used to free it. | ||
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| globalThis.leaked = null; | ||
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| (function () { | ||
| async function step() { | ||
| const d = Promise.withResolvers(); | ||
| globalThis.leaked = () => d; // escapes, capturing the coroutine local `d` | ||
| await d.promise; // suspend: reachable only via leaked -> d | ||
| } | ||
| step(); | ||
| })(); | ||
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| std.gc(); | ||
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| // If the suspended coroutine's frame was wrongly collected, `d` is freed memory. | ||
| const d = leaked(); | ||
| assert(typeof d.resolve, "function"); | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,28 @@ | ||
| import * as std from "qjs:std"; | ||
| import { assert } from "./assert.js"; | ||
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| // Regression test: a suspended coroutine kept reachable only through its mapped | ||
| // `arguments` object must not be collected. | ||
| // | ||
| // A sloppy function with a simple parameter list that uses `arguments` gets a | ||
| // *mapped* arguments object whose entries are open var_refs pointing into the | ||
| // function's frame. That object is a third var_ref holder (besides closures and | ||
| // object var_ref properties) and must be traced the same way; otherwise a | ||
| // suspended coroutine reachable only via an escaped `arguments` is either freed | ||
| // while still live (use-after-free) or wrongly retained (a leak that trips the | ||
| // gc_obj_list check at runtime teardown). | ||
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| globalThis.leaked = null; | ||
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| const AsyncFunction = (async function () {}).constructor; | ||
| const step = AsyncFunction("a", ` | ||
| globalThis.leaked = () => arguments; // escapes, capturing the frame | ||
| const d = Promise.withResolvers(); | ||
| await d.promise; // suspend; never resolved | ||
| `); | ||
| step(123); | ||
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| std.gc(); | ||
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| // If the frame was wrongly collected this reads freed memory. | ||
| assert(leaked()[0], 123); |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,33 @@ | ||
| import * as std from "qjs:std"; | ||
| import { assert } from "./assert.js"; | ||
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| // Regression test: a suspended generator kept reachable only through a closure | ||
| // that captured one of its locals must not be collected. | ||
| // | ||
| // This is the sync-generator counterpart of suspended-coroutine-closure-gc.js: | ||
| // there is no promise involved. The generator object is held in a cycle through | ||
| // a captured local, and the escaped closure is the only external anchor. The | ||
| // closure holds an open var_ref into the generator's (heap) frame; if that edge | ||
| // is invisible to the cycle collector the generator and its frame are freed | ||
| // while the closure still points into them. | ||
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| globalThis.leaked = null; | ||
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| (function () { | ||
| let g; | ||
| function* gen() { | ||
| const o = {}; | ||
| o.g = g; // frame local -> generator object (a cycle) | ||
| globalThis.leaked = () => o; // escapes, capturing the frame local `o` | ||
| yield; // suspend | ||
| } | ||
| g = gen(); | ||
| g.next(); // run to the yield | ||
| g = null; // now reachable only via the cycle + leaked | ||
| })(); | ||
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| std.gc(); | ||
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| const o = leaked(); | ||
| assert(o.g !== null && o.g !== undefined); // the generator object is still alive | ||
| o.g.next(); // resume it: touches its frame |
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Isn't this implied by
!var_ref->detached && var_ref->stack_frame->cur_gc_obj != NULL? If that's the case, it'd be better to removeis_coroand have something likebool js_is_coro(JSVarRef *vr).There was a problem hiding this comment.
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Updated the comment, it can't because it changes over time.