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diff --git a/doc/rcs/cvs/discussion.mdwn b/doc/rcs/cvs/discussion.mdwn new file mode 100644 index 000000000..645b2388b --- /dev/null +++ b/doc/rcs/cvs/discussion.mdwn @@ -0,0 +1,149 @@ +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 <directory>" call and avoid doing anything in that case? +--[[Joey]] + +> The wrapper wrapper does three things: +> +> 7. It ignores `cvs add <directory>`, since this is a weird CVS +> behavior that ikiwiki gets confused by and doesn't need to act on. +> 7. 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". +> 7. 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]] + +>> Done. --[[schmonz]]. |