1341088 - Support validation of OpenType Variation font tables

Status: RESOLVED FIXED

(Core :: Graphics: Text, defect, P3)

Description

[Jonathan Kew [:jfkthame]]

Currently, the version of OTS we're using doesn't know about OpenType Variations tables.[1]

We should fix that, so that we don't risk passing corrupt/malicious tables to the font rasterizers.


[1] https://www.microsoft.com/typography/otspec/otvaroverview.htm

Comment 1

[Jonathan Kew [:jfkthame]]

I've submitted a PR to upstream OTS with an initial effort at validation of the Variations tables: https://github.com/khaledhosny/ots/pull/164.

Comment 2

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Presumably once this lands, the keep_variation_tables preference being flipped in bug 1447163 would need to be... removed?

Comment 3

[Jonathan Kew [:jfkthame]]

Right, that will be redundant once OTS handles them.

Comment 4

[Jonathan Kew [:jfkthame]]

Attachment: Update OTS to upstream rev. a833113924, which includes support for variation tables

Support for validating these tables has now landed upstream, so let's pull it into gecko as well.

Comment 5

[Jonathan Kew [:jfkthame]]

Attachment: Enable validation of opentype variation tables in downloadable fonts, and replace the keep_variation_tables pref with validate_variation_tables (default=true)

Comment 6

[Jonathan Kew [:jfkthame]]

Rather than just removing the pref, I've replaced it with one that can be used to bypass validation for these tables (just like we can for the OpenType Layout tables), which may be useful for testing purposes (particularly if we run into flaws in the validator). But my assumption is that validation will stay turned on by default, so that we have some protection against exposing the various rasterizers to random bad data in these font tables.

Comment 7

[Jonathan Kew [:jfkthame]]

Try run: https://treeherder.mozilla.org/#/jobs?repo=try&revision=bb47d7f36ea26cbe2f05dacec08a18f74f10c5b1

Comment 8

[Jonathan Kew [:jfkthame]]

Note that as the variation-font support only just landed upstream, there are likely to be minor fixes over the next few days as it gets a fuzzing workout, etc. At this point there are three small fixes pending in https://github.com/khaledhosny/ots/pull/165, and I fully expect there will be a few more of a similar nature.

So I intend to update the patch here with these fixes in the new code, as and when they get found/fixed/tested upstream.

Comment 9

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/c033871a13d0
Update OTS to upstream rev. 63ff19f4a8, which includes support for variation tables. r=jrmuizel
https://hg.mozilla.org/integration/mozilla-inbound/rev/d85e4be1d787
Enable validation of opentype variation tables in downloadable fonts, and replace the keep_variation_tables pref with validate_variation_tables (default=true). r=jrmuizel

Comment 10

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/c033871a13d0
https://hg.mozilla.org/mozilla-central/rev/d85e4be1d787