Intent to Implement and Ship: Limit characters allowed in extensions in File System Access API file pickers

[Marijn Kruisselbrink]

Contact emails

m...@chromium.org

Explainer

https://github.com/WICG/file-system-access/pull/252

Specification

https://github.com/WICG/file-system-access/pull/252

API spec

Yes

Summary

To improve security, the File System Access API's showOpenFilePicker and showSaveFilePicker will limit what characters are allowed in extensions for accepted file types.

Specifically only A-Z, a-z, 0-9, + and . will be allowed, extensions can't end in .local or .lnk, and can't be more than 16 characters long.

Blink component

Blink>Storage>FileSystem

TAG review

https://github.com/w3ctag/design-reviews/issues/580

TAG review status

Pending (but since this addresses a security issue we would like to ship this without blocking on getting TAG review completed. We will try to address any feedback we would get later).

Risks

Interoperability and Compatibility

Gecko: No signal (https://github.com/mozilla/standards-positions/issues/154) This modifies the File System Access API, for which Firefox hasn't yet expressed an official position.

WebKit: Negative (https://lists.webkit.org/pipermail/webkit-dev/2020-August/031362.html)

Web developers: No signals

Security

This is a mitigation for a potential security issue with the initially shipped feature.

Is this feature fully tested by web-platform-tests?

Yes

Link to entry on the Chrome Platform Status

https://www.chromestatus.com/feature/4768827940274176

[Alex Russell]

LGTM1

[yo...@yoav.ws]

It's not clear to me that this is web exposed. Is it?

[Marijn Kruisselbrink]

Calls such as showSaveFilePicker({types: {accept: { 'my/type': ['.db$']}}) (i.e. ones with extensions using characters we no longer allow) would previously work, but with this change will instead reject. So yes, this is web exposed.

[Daniel Bratell]

LGTM1

/Daniel

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[Daniel Bratell]

Make that LGTM2 since Alex had already sent an LGTM1.

/Daniel

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[Yoav Weiss]

LGTM3

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