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Use "least restrictive" directive instead of prefetch-src #582

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merged 8 commits into from
Jan 10, 2023
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Use "least restrictive" directive instead of prefetch-src #582

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Use "least restrictive" directive instead of `prefetch-src`
noamr Dec 19, 2022
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101 changes: 28 additions & 73 deletions index.bs
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Expand Up @@ -2156,7 +2156,6 @@ this algorithm returns normally if compilation is allowed, and throws a
<a>img-src</a> <a grammar>'self'</a>;
<a>manifest-src</a> <a grammar>'self'</a>;
<a>media-src</a> <a grammar>'self'</a>;
<a>prefetch-src</a> <a grammar>'self'</a>;
<a>object-src</a> <a grammar>'self'</a>;
<a>script-src-elem</a> <a grammar>'self'</a>;
<a>script-src-attr</a> <a grammar>'self'</a>;
Expand Down Expand Up @@ -2186,7 +2185,6 @@ this algorithm returns normally if compilation is allowed, and throws a
<a>img-src</a> <a grammar>'self'</a>;
<a>manifest-src</a> <a grammar>'self'</a>;
<a>media-src</a> <a grammar>'self'</a>;
<a>prefetch-src</a> <a grammar>'self'</a>;
<a>object-src</a> <a grammar>'self'</a>;
<a>script-src-elem</a> https://example.com;
<a>script-src-attr</a> <a grammar>'self'</a>;
Expand Down Expand Up @@ -2703,74 +2701,6 @@ this algorithm returns normally if compilation is allowed, and throws a

4. Return "`Allowed`".

<h4 id="directive-prefetch-src">`prefetch-src`</h4>
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I think you'll also need to modify https://w3c.github.io/webappsec-csp/#effective-directive-for-a-request and https://w3c.github.io/webappsec-csp/#directive-fallback-list.

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Done


The <dfn export>prefetch-src</dfn> directive restricts the URLs from which resources may be
prefetched or prerendered. The syntax for the directive's name and value is described by the
following ABNF:

<pre>
directive-name = "prefetch-src"
directive-value = <a grammar>serialized-source-list</a>
</pre>

<div class="example">
Given a page with the following Content Security Policy:

<pre>
<a http-header>Content-Security-Policy</a>: <a>prefetch-src</a> https://example.com/
</pre>

Fetches for the following code will return network errors, as the URLs provided do not match
`prefetch-src`'s <a>source list</a>:

<pre highlight="html">
&lt;link rel="prefetch" src="https://example.org/"&gt;&lt;/link&gt;
&lt;link rel="prerender" src="https://example.org/"&gt;&lt;/link&gt;
</pre>
</div>

<h5 algorithm id="prefetch-src-pre-request">
`prefetch-src` Pre-request check
</h5>

This directive's <a for="directive">pre-request check</a> is as follows:

Given a <a for="/">request</a> (|request|) and a <a for="/">policy</a> (|policy|):

1. Let |name| be the result of executing [[#effective-directive-for-a-request]]
on |request|.

2. If the result of executing [[#should-directive-execute]] on |name|,
`prefetch-src` and |policy| is "`No`", return "`Allowed`".

3. If the result of executing [[#match-request-to-source-list]] on |request|,
this directive's [=directive/value=], and |policy|,
is "`Does Not Match`", return "`Blocked`".

4. Return "`Allowed`".

<h5 algorithm id="prefetch-src-post-request">
`prefetch-src` Post-request check
</h5>

This directive's <a for="directive">post-request check</a> is as follows:

Given a <a for="/">request</a> (|request|), a <a>response</a> (|response|), and a
<a for="/">policy</a> (|policy|):

1. Let |name| be the result of executing [[#effective-directive-for-a-request]]
on |request|.

2. If the result of executing [[#should-directive-execute]] on |name|,
`prefetch-src` and |policy| is "`No`", return "`Allowed`".

3. If the result of executing [[#match-response-to-source-list]] on |response|,
|request|, this directive's [=directive/value=], and |policy|,
is "`Does Not Match`", return "`Blocked`".

4. Return "`Allowed`".

<h4 id="directive-script-src">`script-src`</h4>

The <dfn export>script-src</dfn> directive restricts the locations from which scripts
Expand Down Expand Up @@ -3794,16 +3724,41 @@ this algorithm returns normally if compilation is allowed, and throws a
algorithm returns the violated <a>directive</a> if the request violates the
policy, and "`Does Not Violate`" otherwise.

1. Let |violates| be "`Does Not Violate`".
1. If |request|'s [=request/initiator=] is "`prefetch`", then return the result of executing
[[#does-resource-hint-violate-policy]] on |request| and |policy|.

2. <a for=set>For each</a> |directive| of |policy|:
2. Let |violates| be "`Does Not Violate`".

3. <a for=set>For each</a> |directive| of |policy|:

1. Let |result| be the result of executing |directive|'s
<a for="directive">pre-request check</a> on |request| and |policy|.

2. If |result| is "`Blocked`", then let |violates| be |directive|.

3. Return |violates|.
4. Return |violates|.

<h5 id="does-resource-hint-violate-policy">
Does resource hint |request| violate |policy|?
</h5>

Given a <a for="/">request</a> (|request|) and a <a for="/">policy</a> (|policy|), this
algorithm returns the default <a>directive</a> if the resource-hint request violates all the
policies, and "`Does Not Violate`" otherwise.

1. Let |defaultDirective| be |policy|'s first [=directive=] whose [=directive/name=] is
"`default-src`".

2. If |defaultDirective| does not exist, return "`Does Not Violate`".

3. <a for=set>For each</a> |directive| of |policy|:

1. Let |result| be the result of executing |directive|'s
<a for="directive">pre-request check</a> on |request| and |policy|.

2. If |result| is "`Allowed`", then return "`Does Not Violate`".

4. Return "`Blocked`".

<h5 id="match-nonce-to-source-list" algorithm>
Does |nonce| match |source list|?
Expand Down