I've started reviewing this, and the main thing I don't like is the
post-commit wrapper wrapper that ikiwiki-makerepo is patched to set up.
That just seems unnecessarily complicated. Why can't ikiwiki itself detect
the "cvs add " call and avoid doing anything in that case?
--[[Joey]]
The wrapper wrapper does three things:
- It ignores
cvs add <directory>, since this is a weird CVS
behavior that ikiwiki gets confused by and doesn't need to act on.
- It prevents
cvs locking against itself: cvs commit takes a
write lock and runs the post-commit hook, which runs cvs update,
which wants a read lock and sleeps forever -- unless the post-commit
hook runs in the background so the commit can "finish".
- It fails silently if the ikiwiki post-commit hook is missing.
CVS doesn't have any magic post-commit filenames, so hooks have to
be configured explicitly. I don't think a commit will actually fail
if a configured post-commit hook is missing (though I can't test
this at the moment).
Thing 1 can probably be handled within ikiwiki, if that seems less
gross to you.
It seems like it might be. You can use a getopt hook to check
@ARGV to see how it was called. --[[Joey]]
This does the trick iff the post-commit wrapper passes its args
along. Committed on my branch. This seems potentially dangerous,
since the args passed to ikiwiki are influenced by web commits.
I don't see an exploit, but for paranoia's sake, maybe the wrapper
should only be built with execv() if the cvs plugin is loaded?
--[[schmonz]]
Hadn't considered that. While in wrapper mode the normal getopt is not
done, plugin getopt still runs, and so any unsafe options that
other plugins support could be a problem if another user runs
the setuid wrapper and passes those options through. --[[Joey]]
I've tried compiling the argument check into the wrapper as
the first thing main() does, and was surprised to find that
this doesn't prevent the cvs add <dir> deadlock in a web
commit. I was convinced this'd be a reasonable solution,
especially if conditionalized on the cvs plugin being loaded,
but it doesn't work. And I stuck debug printfs at the beginning
of all the rcs_foo() subs, and whatever cvs add <dir> is
doing to ikiwiki isn't visible to my plugin, because none of
those subs are getting called. Nuts. Can you think of anything
else that might solve the problem, or should I go back to
generating a minimal wrapper wrapper that checks for just
this one thing? --[[schmonz]]
I don't see how there could possibly be a difference between
ikiwiki's C wrapper and your shell wrapper wrapper here. --[[Joey]]
I was comparing strings overly precisely. Fixed on my branch.
I've also knocked off the two most pressing to-do items. I
think the plugin's ready for prime time. --[[schmonz]]
Thing 2 I'm less sure of. (I'd like to see the web UI return
immediately on save anyway, to a temporary "rebuilding, please wait
if you feel like knowing when it's done" page, but this problem
with CVS happens with any kind of commit, and could conceivably
happen with some other VCS.)
None of the other VCSes let a write lock block a read lock, apparently.
Anyway, re the backgrounding, when committing via the web, the
post-commit hook doesn't run anyway; the rendering is done via the
ikiwiki CGI. It would certianly be nice if it popped up a quick "working"
page and replaced it with the updated page when done, but that's
unrelated; the post-commit
hook only does rendering when committing using the VCS directly. The
backgrounding you do actually seems safe enough -- but tacking
on a " &" to the ikiwiki wrapper call doesn't need a wrapper script,
does it? --[[Joey]]
Nope, it works fine to append it to the CVSROOT/loginfo line.
Fixed on my branch. --[[schmonz]]
Thing 3 I think I did in order to squelch the error messages that
were bollixing up the CGI. It was easy to do this in the wrapper
wrapper, but if that's going away, it can be done just as easily
with output redirection in CVSROOT/loginfo.
--[[schmonz]]
If the error messages screw up the CGI they must go to stdout.
I thought we had stderr even in the the CVS dark ages. ;-) --[[Joey]]
Some messages go to stderr, but definitely not all. That's why
I wound up reaching for IPC::Cmd, to execute the command line
safely while shutting CVS up. Anyway, I've tested what happens
if a configured post-commit hook is missing, and it seems fine,
probably also thanks to IPC::Cmd.
--[[schmonz]]
Further review.. --[[Joey]]
I don't understand what cvs_shquote_commit is
trying to do with the test message, but it seems
highly likely to be insecure; I never trust anything
that relies on safely quoting user input passed to the shell.
(As an aside, shell_quote can die on certian inputs.)
Seems to me that, if IPC::Cmd exposes input to the shell
(which I have not verified but its docs don't specify; a bad sign)
you chose the wrong tool and ended up doing down the wrong
route, dragging in shell quoting problems and fixes. Since you
chose to use IPC::Cmd just because you wanted to shut
up CVS stderr, my suggestion would be to use plain system
to run the command, with stderr temporarily sent to /dev/null:
open(my $savederr, ">&STDERR");
open(STDERR, ">", "/dev/null");
my $ret=system("cvs", "-Q", @_);
open(STDERR, ">$savederr");
cvs_runcvs should not take an array reference. It's
usual for this type of function to take a list of parameters
to pass to the command.
Thanks for reading carefully. I've tested your suggestions and
applied them on my branch. --[[schmonz]]
I've abstracted out CVS's involvement in the wrapper, adding a new
"wrapperargcheck" hook to examine argc/argv and return success or
failure (failure causes the wrapper to terminate) and implementing
this hook in the plugin. In the non-CVS case, the check immediately
returns success, so the added overhead is just a function call.
Given how rarely anything should need to reach in and modify the
wrapper -- I'd go so far as to say we shouldn't make it too easy
-- I don't think it's worth the effort to try and design a more
general-purpose way to do so. If and when some other problem thinks
it wants to be solved by a new wrapper hook, it's easy enough to add
one. Until then, I'd say it's more important to keep the wrapper as
short and clear as possible. --[[schmonz]]
I've committed a slightly different hook, which should be general enough
that IkiWiki::Receive can also use it, so please adapt your code to
that. --[[Joey]]
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