[PATCH] D46035: [clangd] Fix unicode handling, using UTF-16 where LSP requires it.

[Sam McCall via Phabricator via cfe-commits]

sammccall added inline comments.


================
Comment at: clang-tools-extra/trunk/clangd/SourceCode.cpp:38
+    // 0xxx is ASCII, handled above. 10xxx is a trailing byte, invalid here.
+    // 11111xxx is not valid UTF-8 at all. Assert because it's probably our bug.
+    assert((UTF8Length >= 2 && UTF8Length <= 4) &&
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benhamilton wrote:
> sammccall wrote:
> > benhamilton wrote:
> > > This is user input, right? Have we actually checked for valid UTF-8, or do we just assume it's valid?
> > > 
> > > If not, it seems like an assertion is not the right check, but we should reject it when we're reading the input.
> > > 
> > Yeah, I wasn't sure about this, offline discussion tentatively concluded we wanted an assert, but I'm happy to switch to something else.
> > 
> > We don't validate the code on the way in, so strings are "bytes of presumed-UTF8". This is usually not a big pain actually. But we could/should certainly make the JSON parser validate the UTF-8. (If we want to go this route, D45753 should be resolved first).
> > 
> > There's two ways the assertion could fire: the code is invalid UTF-8, or there's a bug in the unicode logic here. I thought the latter was more likely at least in the short-term :) and this is the least invasive way to catch it. And if a developer build (assert-enabled) crashes because an editor feeds it invalid bytes, then that's probably better than doing nothing (though not as good as catching the error earlier).
> The problem with not validating is it's easy to cause OOB memory access (and thus security issues) if someone crafts malicious UTF-8 and makes us read off the end of a string.
> 
> We should be clear about the status of all strings in the documentation to APIs.
You still have to find/write a UTF-8 decoder that doesn't check bounds, which is (hopefully!) the harder part of writing that bug :-)
But I agree in principle, there's more subtle attacks too, like `C08A` which is invalid but non-validating decoders will treat as a newline.

I have a nearly-finished patch to add real validation to the JSON library, I'll copy you on it.


Repository:
  rL LLVM

https://reviews.llvm.org/D46035