X-Git-Url: http://git.vanrenterghem.biz/git.ikiwiki.info.git/blobdiff_plain/d60c829475123ddb6d258341c270160e4744604a..e71622d233660b5ba305d68e586d7d14ff2124e6:/doc/plugins/contrib/bibtex2html/discussion.mdwn

diff --git a/doc/plugins/contrib/bibtex2html/discussion.mdwn b/doc/plugins/contrib/bibtex2html/discussion.mdwn
index 60fccff9e..3e4207e4e 100644
--- a/doc/plugins/contrib/bibtex2html/discussion.mdwn
+++ b/doc/plugins/contrib/bibtex2html/discussion.mdwn
@@ -35,3 +35,104 @@ Right now, it is not possible for the [[plugins/contrib/compile]] plugin to rend
 >> individual vulnerabilities there involved ImageMagick and GraphicsMagick
 >> running arbitrary shell pipelines from delegates.xml that turned out not
 >> to be hardened against invocation by a hostile user. --[[smcv]]
+
+>>> The `exec` plugin would definitely not be marked as "safe": it
+>>> allows wiki administrators to execute arbitrary code as the wiki
+>>> user.
+>>>
+>>> That said, I believe it is possible to craft a configuration that
+>>> *would* be safe to use for *users* in general. Of course, we can't
+>>> exclude foot-shooting here: if an admin misconfigures the plugin,
+>>> they can introduce new attack vectors. But default and sample
+>>> configurations should be secure.
+>>>
+>>> It is with that model in mind that I wrote the bibtex2html plugin: it doesn't
+>>> use the shell to execute bibtex2html:
+>>>
+>>> [[!format perl """my @bibtex_cmd = (qw[bibtex2html -noheader -nofooter -nobibsource -nodoc -q -o -], $near); open(PIPE, "-|", @bibtex_cmd) || error "can't open pipe to @bibtex_cmd: $!";"""]]
+>>>
+>>> I specifically tried to address that case, to make sure users
+>>> can't execute arbitrary code even if the plugin is enabled.
+>>>
+>>> Still: it is tricky! The above pipeline could *still* be
+>>> vulnerable to certain attacks if bibtex2html does some dangerous
+>>> stuff on its own. For example, it could call other executables
+>>> with the shell without checking arguments, and then the filename
+>>> would be expanded into hostile shell commands. Even worse and
+>>> trickier, the filename could be something like `-oclobberfile` and
+>>> one file would be destroyed!
+>>>
+>>> bibtex2html is probably vulnerable to such an attack right now. We
+>>> should check attachments for weird filenames and restrict what is
+>>> allowed to upload and pass to the plugin.
+>>>
+>>> In case you haven't reviewed the [[compile]] plugin in detail,
+>>> what struck me as an interesting model is the way it allows admin
+>>> to configure extensions to pipeline mappings. What I had in mind
+>>> was something like this:
+>>>
+>>>     exec_pipelines:
+>>>     - bib: 'bibtex2html -o- %s'
+>>>     - svg: 'inkscape -o- %s'
+>>>     - tex:
+>>>       - 'pdflatex %s'
+>>>       - 'bibtex %s'
+>>>       - 'pdflatex %s'
+>>>       - 'pdflatex %s'
+>>>
+>>> (forgive my YAML cluelessness, the idea above is to define a hash
+>>> of extension -> (command) mapping.) The command would be broken up
+>>> on spaces into an array and the `%s` element would be replaced by
+>>> the source file, which would be forbidden to use shell
+>>> metacharacters, including prefixed dashes. I believe such a plugin
+>>> could be crafted to be secure with proper configuration
+>>>
+>>> Of course, it's better if there's a native plugin for
+>>> everything. For bibtex, we need to use Text::Bibtex, for
+>>> example. But that basically means rewriting bibtex2html in Perl,
+>>> which not something any user can do easily. And it's an even worse
+>>> problems for documents like Word spreadsheets or Latex
+>>> documents. Only the native commands can do the right thing.
+>>>
+>>> A clever admin can certainly find out about such a command and
+>>> having a way for that admin to easily hook that into ikiwiki would
+>>> be a powerful tool, with all that implies.  --[[anarcat]]
+
+>>>> Concerning the ability to run arbitrary commands, a [[discussion was
+>>>> started|https://ikiwiki.info/plugins/contrib/compile/discussion/]] by someone
+>>>> who wanted a secure version of this plugin. The idea I had (which has some
+>>>> similarities with what is being discussed here) was to provide a
+>>>> `compile_secure` boolean option to restrict what the user can do (if
+>>>> false, users can run arbitrary commands; if true, users can only run a set of
+>>>> predefined commands). However, since [[fr33domlover]], who started the
+>>>> discussion, did not answer, nothing was implemented.
+>>>>
+>>>> Concerning arbitrary commands, I do not know Perl, but I think it can run
+>>>> commands using something similar to [exec](http://linux.die.net/man/3/exec),
+>>>> which prevents (?) shell injections. This adds the burden of manipulating
+>>>> arrays instead of strings, but security should be improved.
+>>>>
+>>>> But none of those ideas solve the problems you mentionned, being that
+>>>> external commands can do nasty things (the `-oclobberfile` option of
+>>>> `bibtex2html`) or contain bugs (like ImageMagick).
+>>>>
+>>>> If we want to merge this plugin and compile, I think a better idea than the one
+>>>> I proposed at the beginning of the discussion would be to provide two different
+>>>> directives: a `\[[!compile "foo.bar"]]` would compile the file and render it as a
+>>>> link to the compiled file (what the compile plugin does right now), while
+>>>> `\[[!render "foo.bar"]]` would compile the file,
+>>>> and render its content in the current page (whath the bibtex2html plugin
+>>>> does). In fact, providing this
+>>>> `\[[!render ...]]` directive (without the security considerations) seems
+>>>> easy enough to implement, and I might implement it some day (soon, if it
+>>>> solves [[anarcat]] problem and closes the discussion).
+>>>>
+>>>> While I am really happy to see that my plugin sparks some interest, I fear I
+>>>> won't be able to implement what is discussed here, apart from the quick
+>>>> feature I mentionned in the previous paragraph (I have a baby at home, I am
+>>>> moving to another city in a few weeks, and the only code I ever wrote in Perl
+>>>> was to contribute to IkiWiki). However, you have my blessing for making
+>>>> whatever you want with my code: contribute, write a version 2 of it, write a
+>>>> new plugin that makes it obsolete, copy the good ideas and dump the rest, etc.
+>>>>
+>>>> --[[Louis|spalax]]