diff options
Diffstat (limited to 'doc/plugins')
| -rw-r--r-- | doc/plugins/po.mdwn | 289 |
1 files changed, 266 insertions, 23 deletions
diff --git a/doc/plugins/po.mdwn b/doc/plugins/po.mdwn index 923ccd63a..544c7ef62 100644 --- a/doc/plugins/po.mdwn +++ b/doc/plugins/po.mdwn @@ -6,6 +6,8 @@ gettext, using [po4a](http://po4a.alioth.debian.org/). It depends on the Perl `Locale::Po4a::Po` library (`apt-get install po4a`). +[[!toc levels=2]] + Introduction ============ @@ -127,6 +129,10 @@ Usage Templates --------- +When `po_link_to` is not set to `negotiated`, one should replace some +occurrences of `BASEURL` with `HOMEPAGEURL` to get correct links to +the wiki homepage. + The `ISTRANSLATION` and `ISTRANSLATABLE` variables can be used to display things only on translatable or translation pages. @@ -215,10 +221,229 @@ TODO Security checks --------------- -- Can any sort of directives be put in po files that will - cause mischief (ie, include other files, run commands, crash gettext, - whatever). -- Any security issues on running po4a on untrusted content? +### Security history + +The only past security issues I could find in GNU gettext and po4a +are: + +- [CVE-2004-0966](http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2004-0966), + *i.e.* [Debian bug #278283](http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=278283): + the autopoint and gettextize scripts in the GNU gettext package + 1.14 and later versions, as used in Trustix Secure Linux 1.5 + through 2.1 and other operating systems, allows local users to + overwrite files via a symlink attack on temporary files. +- [CVE-2007-4462](http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-4462): + `lib/Locale/Po4a/Po.pm` in po4a before 0.32 allows local users to + overwrite arbitrary files via a symlink attack on the + gettextization.failed.po temporary file. + +**FIXME**: check whether this plugin would have been a possible attack +vector to exploit these vulnerabilities. + +Depending on my mood, the lack of found security issues can either +indicate that there are none, or reveal that no-one ever bothered to +find (and publish) them. + +### PO file features + +Can any sort of directives be put in po files that will cause mischief +(ie, include other files, run commands, crash gettext, whatever)? + +> No [documented](http://www.gnu.org/software/gettext/manual/gettext.html#PO-Files) +> directive is supposed to do so. [[--intrigeri]] + +### Running po4a on untrusted content + +Are there any security issues on running po4a on untrusted content? + +To say the least, this issue is not well covered, at least publicly: + +- the documentation does not talk about it; +- grep'ing the source code for `security` or `trust` gives no answer. + +On the other hand, a po4a developer answered my questions in +a convincing manner, stating that processing untrusted content was not +an initial goal, and analysing in detail the possible issues. + +#### Already checked + +- the core (`Po.pm`, `Transtractor.pm`) should be safe +- po4a source code was fully checked for other potential symlink + attacks, after discovery of one such issue +- the only external program run by the core is `diff`, in `Po.pm` (in + parts of its code we don't use) +- `Locale::gettext`: only used to display translated error messages +- Nicolas François "hopes" `DynaLoader` is safe, and has "no reason to + think that `Encode` is not safe" +- Nicolas François has "no reason to think that `Encode::Guess` is not + safe". The po plugin nevertheless avoids using it by defining the + input charset (`file_in_charset`) before asking `Transtractor` to + read any file. NB: this hack depends on po4a internals to stay + the same. + +#### To be checked + +##### Locale::Po4a modules + +The modules we want to use have to be checked, as not all are safe +(e.g. the LaTeX module's behaviour is changed by commands included in +the content); they may use regexps generated from the content. + +`Chooser.pm` only loads the plugin we tell it too: currently, this +means the `Text` module only. + +`Text` module (I checked the CVS version): + +- it does not run any external program +- only `do_paragraph()` builds regexp's that expand untrusted + variables; they seem safe to me, but someone more expert than me + will need to check. Joey? + +##### Text::WrapI18N + +`Text::WrapI18N` can cause DoS (see the +[Debian bug #470250](http://bugs.debian.org/470250)), but it is +optional and we do not need the features it provides. + +It is loaded if available by `Locale::Po4a::Common`; looking at the +code, I'm not sure we can prevent this at all, but maybe some symbol +table manipulation tricks could work; overriding +`Locale::Po4a::Common::wrapi18n` may be easier. I'm no expert at all +in this field. Joey? [[--intrigeri]] + +> Update: Nicolas François suggests we add an option to po4a to +> disable it. It would do the trick, but only for people running +> a brand new po4a (probably too late for Lenny). Anyway, this option +> would have to take effect in a `BEGIN` / `eval` that I'm not +> familiar with. I can learn and do it, in case no Perl wizard +> volunteers to provide the po4a patch. [[--intrigeri]] + +##### Term::ReadKey + +`Term::ReadKey` is not a hard dependency in our case, *i.e.* po4a +works nicely without it. But the po4a Debian package recommends +`libterm-readkey-perl`, so it will probably be installed on most +systems using the po plugin. + +If `$ENV{COLUMNS}` is not set, `Locale::Po4a::Common` uses +`Term::ReadKey::GetTerminalSize()` to get the terminal size. How safe +is this? + +Part of `Term::ReadKey` is written in C. Depending on the runtime +platform, this function use ioctl, environment, or C library function +calls, and may end up running the `resize` command (without +arguments). + +IMHO, using Term::ReadKey has too far reaching implications for us to +be able to guarantee anything wrt. security. Since it is anyway of no +use in our case, I suggest we define `ENV{COLUMNS}` before loading +`Locale::Po4a::Common`, just to be on the safe side. Joey? +[[--intrigeri]] + +> Update: adding an option to disable `Text::WrapI18N`, as Nicolas +> François suggested, would as a bonus disable `Term::ReadKey` +> as well. [[--intrigeri]] + +### msgmerge + +`refreshpofiles()` runs this external program. A po4a developer +answered he does "not expect any security issues from it". + +### Fuzzing input + +I was not able to find any public information about gettext or po4a +having been tested with a fuzzing program, such as `zzuf` or `fusil`. +Moreover, some gettext parsers seem to be quite +[easy to crash](http://fusil.hachoir.org/trac/browser/trunk/fuzzers/fusil-gettext), +so it might be useful to bang msgmerge/po4a's heads against such +a program in order to easily detect some of the most obvious DoS. +[[--intrigeri]] + +> po4a was not fuzzy-tested, but according to one of its developers, +> "it would be really appreciated". [[--intrigeri]] + +Test conditions: + +- a 21M file containing 100 concatenated copies of all the files in my + `/usr/share/common-licenses/`; I had no existing PO file or + translated versions at hand, which renders these tests + quite incomplete. +- po4a was the Debian 0.34-2 package; the same tests were also run + after replacing the `Text` module with the CVS one (the core was not + changed in CVS since 0.34-2 was released), without any significant + difference in the results. +- Perl 5.10.0-16 + +#### po4a-gettextize + +`po4a-gettextize` uses more or less the same po4a features as our +`refreshpot` function. + +Without specifying an input charset, zzuf'ed `po4a-gettextize` quickly +errors out, complaining it was not able to detect the input charset; +it leaves no incomplete file on disk. + +So I had to pretend the input was in UTF-8, as does the po plugin. + +Two ways of crashing were revealed by this command-line: + + zzuf -vc -s 0:100 -r 0.1:0.5 \ + po4a-gettextize -f text -o markdown -M utf-8 -L utf-8 \ + -m LICENSES >/dev/null + +They are: + + Malformed UTF-8 character (UTF-16 surrogate 0xdcc9) in substitution iterator at /usr/share/perl5/Locale/Po4a/Po.pm line 1443. + Malformed UTF-8 character (fatal) at /usr/share/perl5/Locale/Po4a/Po.pm line 1443. + +and + + Malformed UTF-8 character (UTF-16 surrogate 0xdcec) in substitution (s///) at /usr/share/perl5/Locale/Po4a/Po.pm line 1443. + Malformed UTF-8 character (fatal) at /usr/share/perl5/Locale/Po4a/Po.pm line 1443. + +Perl seems to exit cleanly, and an incomplete PO file is written on +disk. I not sure whether if this is a bug in Perl or in `Po.pm`. + +#### po4a-translate + +`po4a-translate` uses more or less the same po4a features as our +`filter` function. + +Without specifying an input charset, same behaviour as +`po4a-gettextize`, so let's specify UTF-8 as input charset as of now. + + zzuf -cv \ + po4a-translate -d -f text -o markdown -M utf-8 -L utf-8 \ + -k 0 -m LICENSES -p LICENSES.fr.po -l test.fr + +... prints tons of occurences of the following error, but a complete +translated document is written (obviously with some weird chars +inside): + + Use of uninitialized value in string ne at /usr/share/perl5/Locale/Po4a/TransTractor.pm line 854. + Use of uninitialized value in string ne at /usr/share/perl5/Locale/Po4a/TransTractor.pm line 840. + Use of uninitialized value in pattern match (m//) at /usr/share/perl5/Locale/Po4a/Po.pm line 1002. + +While: + + zzuf -cv -s 0:10 -r 0.001:0.3 \ + po4a-translate -d -f text -o markdown -M utf-8 -L utf-8 \ + -k 0 -m LICENSES -p LICENSES.fr.po -l test.fr + +... seems to lose the fight, at the `readpo(LICENSES.fr.po)` step, +against some kind of infinite loop, deadlock, or any similar beast. +It does not seem to eat memory, though. + +Whatever format module is used does not change anything. This is thus +probably a bug in po4a's core or in a lib it depends on. + +The sub `read`, in `TransTractor.pm`, seems to be a good debugging +starting point. + +#### msgmerge + +`msgmerge` is run in our `refreshpofiles` function. I did not manage +to crash it with `zzuf`. gettext/po4a rough corners -------------------------- @@ -227,37 +452,43 @@ gettext/po4a rough corners live in different directories): say bla.fr.po has been updated in repo2; pulling repo2 from repo1 seems to trigger a PO update, that changes bla.fr.po in repo1; then pushing repo1 to repo2 triggers - a PO update, that changes bla.fr.po in repo2; etc.; fixed in - `629968fc89bced6727981c0a1138072631751fee`? + a PO update, that changes bla.fr.po in repo2; etc.; quickly fixed in + `629968fc89bced6727981c0a1138072631751fee`, by disabling references + in Pot files. Using `Locale::Po4a::write_if_needed` might be + a cleaner solution. (warning: this function runs the external + `diff` program, have to check security) - new translations created in the web interface must get proper charset/encoding gettext metadata, else the next automatic PO update removes any non-ascii chars; possible solution: put such metadata into the Pot file, and let it propagate; should be fixed in `773de05a7a1ee68d2bed173367cf5e716884945a`, time will tell. -Misc. improvements ------------------- - -### page titles +Page titles in links +-------------------- -Use nice page titles from meta plugin in links, as inline already -does. This is actually a duplicate for -[[bugs/pagetitle_function_does_not_respect_meta_titles]], which might -be fixed by something like [[todo/using_meta_titles_for_parentlinks]]. +To use the page titles set with the [meta](plugins/meta) plugin when +rendering links would be very much nicer, than the current +"filename.LL" format. This is actually a duplicate for +[[bugs/pagetitle_function_does_not_respect_meta_titles]]. -### backlinks +Page formats +------------ -`po_link_to = negotiated`: if a given translatable `sourcepage.mdwn` -links to \[[destpage]], `sourcepage.LL.po` also link to \[[destpage]], -and the latter has the master page *and* all its translations listed -in the backlinks. +Markdown is well supported, great, but what about others? -`po_link_to = current`: seems to work nicely +The [po](plugins/po) uses `Locale::Po4a::Text` for every page format; +this can be expected to work out of the box with most other wiki-like +formats supported by ikiwiki. Some of their ad-hoc syntax might be +parsed in a strange way, but the worst problems I can imagine would be +wrapping issues; e.g. there is code in po4a dedicated to prevent +re-wrapping the underlined Markdown headers. -### parentlinks +While it would be easy to better support formats such as [[html]] or +LaTeX, by using for each one the dedicated po4a module, this can be +problematic from a security point of view. -When `usedirs` is disabled and the home page is translatable, the -parent link to the wiki home page is broken (`/index.html`). +**TODO**: test the more popular formats and write proper documentation +about it. Translation quality assurance ----------------------------- @@ -270,3 +501,15 @@ A new `cansave` type of hook would be needed to implement this. Note: committing to the underlying repository is a way to bypass this check. + +Broken links +------------ + +See [[contrib/po]]. + +Documentation +------------- + +Maybe write separate documentation depending on the people it targets: +translators, wiki administrators, hackers. This plugin is maybe +complex enough to deserve this. |