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| author | http://smcv.pseudorandom.co.uk/ <http://smcv.pseudorandom.co.uk/@web> | 2010-04-07 02:55:50 +0000 |
|---|---|---|
| committer | Joey Hess <joey@finch.kitenet.net> | 2010-04-07 02:55:50 +0000 |
| commit | 1158fe8f4400943d7a24350c6ac8fee6a95c2bed (patch) | |
| tree | ab6563d0b95f9e2eaa6ffc5e86f8e29790d25a05 | |
| parent | 811d398646337717f8f2ad92897c6410faa42777 (diff) | |
further discussion, point out potential XSS
| -rw-r--r-- | doc/plugins/contrib/field/discussion.mdwn | 110 |
1 files changed, 110 insertions, 0 deletions
diff --git a/doc/plugins/contrib/field/discussion.mdwn b/doc/plugins/contrib/field/discussion.mdwn index b243e2dfe..16b40cf06 100644 --- a/doc/plugins/contrib/field/discussion.mdwn +++ b/doc/plugins/contrib/field/discussion.mdwn @@ -24,10 +24,64 @@ behaviour, an auxiliary plugin would be easy.) >>> Based on `field_get_value()`, yes. That would be my ideal. Do you think I should implement that as an ikiwiki branch? --[[KathrynAndersen]] +>>>> This doesn't solve cases where certain fields are treated specially; for +>>>> instance, putting a `\[[!meta permalink]]` on a page is not the same as +>>>> putting it in `ymlfront` (in the latter case you won't get your +>>>> `<link>` header), and putting `\[[!meta date]]` is not the same as putting +>>>> `date` in `ymlfront` (in the latter case, `%pagectime` won't be changed). +>>>> +>>>> One way to resolve that would be to have `ymlfront`, or similar, be a +>>>> front-end for `meta` rather than for `field`, and call +>>>> `IkiWiki::Plugin::meta::preprocess` (or a refactored-out function that's +>>>> similar). +>>>> +>>>> There are also some cross-site scripting issues (see below)... --[[smcv]] + >> (On the site I mentioned, I'm using an unmodified version of `field`, >> and currently working around the collision by tagging books' pages >> with `bookauthor` instead of `author` in the YAML.) --s +>> Revisiting this after more thought, the problem here is similar to the +>> possibility that a wiki user adds a `meta` shortcut +>> to [[shortcuts]], or conversely, that a plugin adds a `cpan` directive +>> that conflicts with the `cpan` shortcut that pages already use. (In the +>> case of shortcuts, this is resolved by having plugin-defined directives +>> always win.) For plugin-defined meta keywords this is the plugin +>> author's/wiki admin's problem - just don't enable conflicting plugins! - +>> but it gets scary when you start introducing things like `ymlfront`, which +>> allow arbitrary, wiki-user-defined fields, even ones that subvert +>> other plugins' assumptions. +>> +>> The `pagetemplate` hook is particularly alarming because page templates are +>> evaluated in many contexts, not all of which are subject to the +>> htmlscrubber or escaping; because the output from `field` isn't filtered, +>> prefixed or delimited, when combined with an arbitrary-key-setting plugin +>> like `ymlfront` it can interfere with other plugins' expectations +>> and potentially cause cross-site scripting exploits. For instance, `inline` +>> has a `pagetemplate` hook which defines the `FEEDLINKS` template variable +>> to be a blob of HTML to put in the `<head>` of the page. As a result, this +>> YAML would be bad: +>> +>> --- +>> FEEDLINKS: <script>alert('code injection detected')</script> +>> --- +>> +>> (It might require a different case combination due to implementation +>> details, I'm not sure.) +>> +>> It's difficult for `field` to do anything about this, because it doesn't +>> know whether a field is meant to be plain text, HTML, a URL, or something +>> else. +>> +>> If `field`'s `pagetemplate` hook did something more limiting - like +>> only emitting template variables starting with `field_`, or from some +>> finite set, or something - then this would cease to be a problem, I think? +>> +>> `ftemplate` and `getfield` don't have this problem, as far as I can see, +>> because their output is in contexts where the user could equally well have +>> written raw HTML directly; the user can cause themselves confusion, but +>> can't cause harmful output. --[[smcv]] + From a coding style point of view, the `$CamelCase` variable names aren't IkiWiki style, and the `match_foo` functions look as though they could benefit from being thin wrappers around a common `&IkiWiki::Plugin::field::match` @@ -125,3 +179,59 @@ smcv's discuission of field author vs meta author above. --[[Joey]] > So, yes, it does cater to mostly my personal needs, but I think it is more generally useful, also. > --[[KathrynAndersen]] +>> Is it fair to say, then, that `field`'s purpose is to take other +>> plugins' arbitrary per-page data, and present it as a single +>> merged/flattened string => string map per page? From the plugins +>> here, things you then use that merged map for include: +>> +>> * sorting - stolen by [[todo/allow_plugins_to_add_sorting_methods]] +>> * substitution into pages with Perl-like syntax - `getfield` +>> * substitution into wiki-defined templates - the `pagetemplate` +>> hook +>> * substitution into user-defined templates - `ftemplate` +>> +>> As I mentioned above, the flattening can cause collisions (and in the +>> `pagetemplate` case, even security problems). +>> +>> I wonder whether conflating Page Text Variables with Page Variables +>> causes `field` to be more general than it needs to be? +>> To define a Page Variable (function-like field), you need to write +>> a plugin containing that Perl function; if we assume that `field` +>> or something resembling it gets merged into ikiwiki, then it's +>> reasonable to expect third-party plugins to integrate with whatever +>> scaffolding there is for these (either in an enabled-by-default +>> plugin that most people are expected to leave enabled, like `meta` +>> now, or in the core), and it doesn't seem onerous to expect each +>> plugin that wants to participate in this mechanism to have code to +>> do so. While it's still contrib, `field` could just have a special case +>> for the meta plugin, rather than the converse? +>> +>> If Page Text Variables are limited to being simple strings as you +>> suggest over in [[forum/an_alternative_approach_to_structured_data]], +>> then they're functionally similar to `meta` fields, so one way to +>> get their functionality would be to extend `meta` so that +>> +>> \[[!meta badger="mushroom"]] +>> +>> (for an unrecognised keyword `badger`) would store +>> `$pagestate{$page}{meta}{badger} = "mushroom"`? Getting this to +>> appear in templates might be problematic, because a naive +>> `pagetemplate` hook would have the same problem that `field` combined +>> with `ymlfront` currently does. +>> +>> One disadvantage that would appear if the function-like and +>> meta-like fields weren't in the same namespace would be that it +>> wouldn't be possible to switch a field from being meta-like to being +>> function-like without changing any wiki content that referenced it. +>> +>> Perhaps meta-like fields should just *be* `meta` (with the above +>> enhancement), as a trivial case of function-like fields? That would +>> turn `ymlfront` into an alternative syntax for `meta`, I think? +>> That, in turn, would hopefully solve the special-fields problem, +>> by just delegating it to meta. I've been glad of the ability to define +>> new ad-hoc fields with this plugin without having to write an extra plugin +>> to do so (listing books with a `bookauthor` and sorting them by +>> `"field(bookauthor) title"`), but that'd be just as easy if `meta` +>> accepted ad-hoc fields? +>> +>> --[[smcv]] |