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Integrate Trusted Types enforcement into attribute handling #1268

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a665ee4
Trusted Types
lukewarlow Apr 24, 2025
d86e02f
Revert change to "set an attribute value"
lukewarlow Apr 24, 2025
1d25719
Update setAttributeNS to include TT check
lukewarlow Apr 24, 2025
15e9f57
Remove extra algorithm that called through to TT and call TT directly…
lukewarlow Jun 25, 2025
aaaae9c
Revert larger change to setAttributeNs as its no longer neccessary.
lukewarlow Jul 3, 2025
4ed8160
Set attr's value to verifiedValue before attribute change steps are f…
lukewarlow Jul 3, 2025
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55 changes: 45 additions & 10 deletions dom.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -54,9 +54,11 @@ spec:html; type:element
<p>This specification depends on the Infra Standard. [[!INFRA]]

<p>Some of the terms used in this specification are defined in <cite>Encoding</cite>,
<cite>Selectors</cite>, <cite>Web IDL</cite>, <cite>XML</cite>, and <cite>Namespaces in XML</cite>.
<cite>Selectors</cite>, <cite>Trusted Types</cite>, <cite>Web IDL</cite>, <cite>XML</cite>, and
<cite>Namespaces in XML</cite>.
[[!ENCODING]]
[[!SELECTORS4]]
[[!TRUSTED-TYPES]]
[[!WEBIDL]]
[[!XML]]
[[!XML-NAMES]]
Expand Down Expand Up @@ -6520,8 +6522,8 @@ interface Element : Node {
sequence&lt;DOMString> getAttributeNames();
DOMString? getAttribute(DOMString qualifiedName);
DOMString? getAttributeNS(DOMString? namespace, DOMString localName);
[CEReactions] undefined setAttribute(DOMString qualifiedName, DOMString value);
[CEReactions] undefined setAttributeNS(DOMString? namespace, DOMString qualifiedName, DOMString value);
[CEReactions] undefined setAttribute(DOMString qualifiedName, (TrustedType or DOMString) value);
[CEReactions] undefined setAttributeNS(DOMString? namespace, DOMString qualifiedName, (TrustedType or DOMString) value);
[CEReactions] undefined removeAttribute(DOMString qualifiedName);
[CEReactions] undefined removeAttributeNS(DOMString? namespace, DOMString localName);
[CEReactions] boolean toggleAttribute(DOMString qualifiedName, optional boolean force);
Expand Down Expand Up @@ -6998,6 +7000,11 @@ string <var>namespace</var> (default null):</p>
<a for=/>attribute</a> <var>attr</var> and an <a for=/>element</a> <var>element</var>:

<ol>
<li><p>Let <var>verifiedValue</var> be the result of calling <a abstract-op>get
Trusted Types-compliant attribute value</a> with <var>attr</var>'s <a for=Attr>local name</a>,
<var>attr</var>'s <a for=Attr>namespace</a>, <var>element</var>, and <var>attr</var>'s
<a for=Attr>value</a>. [[!TRUSTED-TYPES]]

<li><p>If <var>attr</var>'s <a for=Attr>element</a> is neither null nor <var>element</var>,
<a>throw</a> an "{{InUseAttributeError!!exception}}" {{DOMException}}.

Expand All @@ -7013,6 +7020,8 @@ string <var>namespace</var> (default null):</p>

<li><p>Otherwise, <a lt="append an attribute">append</a> <var>attr</var> to <var>element</var>.

<li><p>Set <var>attr</var>'s <a for=Attr>value</a> to <var>verifiedValue</var>.
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Need to check if this is in the right place in the algorithm.

cc @fred-wang

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(1) So in case oldAttr == attr, its value isn't updated.

(2) 'append an attribute' calls 'Handle attribute changes', and verifiedValue is set to attr after that. That doesn't seem right. Shouldn't value be set before?

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@lukewarlow lukewarlow Jul 3, 2025 •
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  1. So in case oldAttr == attr, its value isn't updated.

Yes, I think that makes sense? If the attribute hasn't changed does it make sense to put it through Trusted Types default policy? I'll double check what browsers actually do in this case though.

  1. 'append an attribute' calls 'Handle attribute changes', and verifiedValue is set to attr after that. That doesn't seem right. Shouldn't value be set before?

Ah yeah, you're right, step 7 should be moved to step 5.

I've fixed 2 now.

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So I double checked and for point 1 there's actually an interop bug here, WebKit (and Gecko) doesn't throw a TT error. Chromium currently does, so we can choose whichever behaviour we think is best here.

cc @annevk and @otherdaniel for your opinions

TLDR should doing

element.setAttributeNode(element.attributes[1]) - throw a TT error when TT is enforced (and where element.attributes[1] is something like an onclick attribute?

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I think we either have to throw or do nothing at all, right? The latter is very weird as even no-op mutations result in a mutation record being queued. And queuing a mutation record for trusted type attributes without validation having occurred seems bad, so I think we have to throw.


<li><p>Return <var>oldAttr</var>.
</ol>
</div>
Expand Down Expand Up @@ -7291,17 +7300,21 @@ method steps are:
<a>HTML document</a>, then set <var>qualifiedName</var> to <var>qualifiedName</var> in
<a>ASCII lowercase</a>.

<li><p>Let <var>verifiedValue</var> be the result of calling <a abstract-op>get
Trusted Types-compliant attribute value</a> with <var>qualifiedName</var>, null, <a>this</a>, and
<var>value</var>. [[!TRUSTED-TYPES]]

<li><p>Let <var>attribute</var> be the first <a>attribute</a> in <a>this</a>'s
<a for=Element>attribute list</a> whose <a for=Attr>qualified name</a> is <var>qualifiedName</var>,
and null otherwise.
<!-- This is step 2 of "get an attribute by name", modified as appropriate -->

<li><p>If <var>attribute</var> is null, create an <a>attribute</a> whose
<a for=Attr>local name</a> is <var>qualifiedName</var>, <a for=Attr>value</a> is
<var>value</var>, and <a for=Node>node document</a> is <a>this</a>'s <a for=Node>node document</a>,
then <a lt="append an attribute">append</a> this <a>attribute</a> to <a>this</a>, and then return.
<var>verifiedValue</var>, and <a for=Node>node document</a> is <a>this</a>'s
<a for=Node>node document</a>, then <a lt="append an attribute">append</a> this <a>attribute</a>
to <a>this</a>, and then return.

<li><p><a lt="change an attribute">Change</a> <var>attribute</var> to <var>value</var>.
<li><p><a lt="change an attribute">Change</a> <var>attribute</var> to <var>verifiedValue</var>.
</ol>

<p>The
Expand All @@ -7312,8 +7325,12 @@ method steps are:
<li><p>Let <var>namespace</var>, <var>prefix</var>, and <var>localName</var> be the result of
passing <var>namespace</var> and <var>qualifiedName</var> to <a>validate and extract</a>.

<li><p><a>Set an attribute value</a> for <a>this</a> using <var>localName</var>, <var>value</var>,
and also <var>prefix</var> and <var>namespace</var>.
<li><p>Let <var>verifiedValue</var> be the result of calling <a abstract-op>get
Trusted Types-compliant attribute value</a> with <var>localName</var>, <var>namespace</var>,
<var>element</var>, and <var>value</var>. [[!TRUSTED-TYPES]]

<li><p><a>Set an attribute value</a> for <a>this</a> using <var>localName</var>,
<var>verifiedValue</var>, and also <var>prefix</var> and <var>namespace</var>.
</ol>

<p>The
Expand Down Expand Up @@ -7891,7 +7908,25 @@ string <var>value</var>, run these steps:
<li><p>If <var>attribute</var>'s <a for=Attr>element</a> is null, then set <var>attribute</var>'s
<a for=Attr>value</a> to <var>value</var>.

<li><p>Otherwise, <a lt="change an attribute">change</a> <var>attribute</var> to <var>value</var>.
<li>
<p>Otherwise:

<ol>
<li><p>Let <var>originalElement</var> be <var>attribute</var>'s <a for=Attr>element</a>.
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Suggested change
<li><p>Let <var>originalElement</var> be <var>attribute</var>'s <a for=Attr>element</a>.
<li><p>Let <var>element</var> be <var>attribute</var>'s <a for=Attr>element</a>.


<li><p>Let <var>verifiedValue</var> be the result of calling <a abstract-op>get
Trusted Types-compliant attribute value</a> with <var>attribute</var>'s
<a for=Attr>local name</a>, <var>attribute</var>'s <a for=Attr>namespace</a>, <a>this</a>,
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There is no this here.

and <var>value</var>. [[!TRUSTED-TYPES]]

<li><p>If <var>attribute</var>'s <a for=Attr>element</a> is null, then set <var>attribute</var>'s
<a for=Attr>value</a> to <var>verifiedValue</var>, and return.

<li><p>If <var>attribute</var>'s <a for=Attr>element</a> is not <var>originalElement</var>, then
return.
Comment on lines +7922 to +7926
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I think it would be nicer if we throw for both of these cases as they result from the policy changing aspects of the attribute that it probably shouldn't? But maybe that's not compatible with what Chromium does.

Also, the other changes are made directly in setAttribute and setAttributeNS. Do we end up invoking the policy early enough here for the various call sites? It seems like there would be a difference in exception order.


<li><p><a lt="change an attribute">Change</a> <var>attribute</var> to <var>verifiedValue</var>.
</ol>
</ol>

<p>The {{Attr/value}} setter steps are to <a>set an existing attribute value</a> with <a>this</a>
Expand Down