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Showing content from https://github.com/gorhill/uBlock/issues/3375 below:

script:inject with only negated domains cause cosmetic filtering engine to crash · Issue #3375 · gorhill/uBlock · GitHub

When a script:inject filter has only negated domains, cosmetic filter parser does not properly discard it.

http://example.com/

1. Add ~example.com##script:inject(abort-on-proerty-read.js, test) to My filters
2. Go to http://example.com/ and open the console

All default

• OS/version: Win10 15063
• Browser/version: Chrome 63
• uBlock Origin version: 1.14.22

All default

See steps to reproduce

Although the crash is caused by an invalid filter, uBO is suppose to discard bad filters.

At around line 365 of cosmetic-filtering.js:

    if (
        this.hostnames.length === 0 &&
        this.unhide === 0 &&
        this.reNeedHostname.test(this.suffix)
    ) {
        this.invalid = true;
        return this;
    }

This is the logic which mark expensive filters as invalid if they are generic. However, it does not handle the case where all domains are negated.

Later, at around line 1175 of cosmetic-filtering.js:

    var applyGlobally = true;
    var hostname;
    while ( i-- ) {
        hostname = hostnames[i];
        if ( hostname.startsWith('~') === false ) {
            applyGlobally = false;
        }
        this.compileHostnameSelector(hostname, parsed, writer);
    }
    if ( applyGlobally ) {
        this.compileGenericSelector(parsed, writer);
    }

When there are only negated domains, applyGlobally will be true and it will use FilterContainer.prototype.compileGenericSelector to compile the filter, which does not expect expensive filters. The compiled data is invalid / corrupted which later cause error in cosmetic filtering engine.

Inside FilterContainer.prototype.compileGenericHideSelector, I see the comment:

// TODO: Detect and error on procedural cosmetic filters.

I'm not sure if you have plan on adding logic to handle it there, but for scriptlet injection, execution won't reach that point (the place where the comment is).

I think the filter should be re-checked for validity inside the if-statement for applyGlobally.

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