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fix image links with escaped brackets #1683

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merged 2 commits into from May 20, 2020
Merged

fix image links with escaped brackets #1683

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48448cc
fix image links with escaped brackets
UziTech May 19, 2020
d57c89d
fix redos
UziTech May 20, 2020
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7 changes: 4 additions & 3 deletions src/Tokenizer.js
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Expand Up @@ -9,22 +9,23 @@ const {
function outputLink(cap, link, raw) {
const href = link.href;
const title = link.title ? escape(link.title) : null;
const text = cap[1].replace(/\\([\[\]])/g, '$1');

if (cap[0].charAt(0) !== '!') {
return {
type: 'link',
raw,
href,
title,
text: cap[1]
text
};
} else {
return {
type: 'image',
raw,
text: escape(cap[1]),
href,
title
title,
text: escape(text)
};
}
}
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2 changes: 1 addition & 1 deletion src/rules.js
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Expand Up @@ -198,7 +198,7 @@ inline.tag = edit(inline.tag)
.replace('attribute', inline._attribute)
.getRegex();

inline._label = /(?:\[[^\[\]]*\]|\\.|`[^`]*`|[^\[\]\\`])*?/;
inline._label = /(?:\[(?:\\.|[^\[\]])*\]|\\.|`[^`]*`|[^\[\]\\`])*?/;
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@davisjam is this regex safe from ReDOS?

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Sadly, it has moved from linear to exponential.

Visualization -- The problem is in the top group. The OR can be satisfied on the top or the bottom using \\a, and if the subsequent ] is missing then you get exponential backtracking.

Example misbehavior:

/\[(?:\\.|[^\[\]])*\]/.exec("[" + "\\a".repeat(300));

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@UziTech UziTech May 20, 2020 •
edited

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what about removing \\ from the second path (/\[(?:\\.|[^\\\[\]])*\]/)? that way the only path it can take is determined by whether it sees a \\

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@davisjam thanks for your help on this. Your regex experience is invaluable.

inline._href = /<(?:\\[<>]?|[^\s<>\\])*>|[^\s\x00-\x1f]*/;
inline._title = /"(?:\\"?|[^"\\])*"|'(?:\\'?|[^'\\])*'|\((?:\\\)?|[^)\\])*\)/;

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11 changes: 11 additions & 0 deletions test/specs/new/image_links.html
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@@ -0,0 +1,11 @@
<p>
<a href="https://example.com/">
<img src="https://example.com/image.jpg" alt="test" title="title" />
</a>
</p>

<p>
<a href="https://example.com/">
<img src="https://example.com/image.jpg" alt="[test]" title="[title]" />
</a>
</p>
3 changes: 3 additions & 0 deletions test/specs/new/image_links.md
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@@ -0,0 +1,3 @@
[![test](https://example.com/image.jpg "title")](https://example.com/)

[![\[test\]](https://example.com/image.jpg "[title]")](https://example.com/)