cgit and symlinks

[john at keeping.me.uk (John Keeping)]

On Wed, Mar 08, 2017 at 02:28:11PM +0100, MonkZ wrote:
> 
> 
> Am 08.03.2017 um 13:30 schrieb John Keeping:
> > On Wed, Mar 08, 2017 at 12:38:38PM +0100, MonkZ wrote:
> >> Am 07.03.2017 um 00:35 schrieb John Keeping:
> >>> We can't reliably follow the link because there is no guarantee that the
> >>> target lies within the repository and I don't know what we would output
> >>> for the case where we can't display the target.
> >>
> >> INADH (I'm not a dev here)
> >>
> >> I would recommend to continue ignoring it or returning the blob, because
> >> following symlinks (internally) might result -  if not done carefully -
> >> in directory traversal security issues. Maybe resolving a symlink to a
> >> HTTP301 could work.
> >>
> >> For the UI there might be a html-link (in a notification box "This is a
> >> symlink that points to ...") to the symlink-destination below or above
> >> the blob, to get a user via click to a file/directory.
> > 
> > We're talking about the "plain" UI here (for example [0]), so we don't
> > have anywhere to put additional content and it has to be something
> > basic.
> Of course. It would be handled like a content-rewrite to return a http301.
> 
> Pseudocode:
> handle_symlinks = True # new config item
> if this_file_is_a_symlink and symlink_is_relative and handle_symlinks:
> 	if plain_ui:
> 		# rewrite blob to http301
> 		# by attaching the path to the end of current basedir
> 		# cgit is already able to handle ../ in a path
> 	if !plain_ui:
> 		# show blob
> 		# show notification that this is a symlink
> 		# show a link to a url
> 		# 	like the one that would be used in plain_ui
> 
> > 
> > I'm not actually too worried about directory traversal if we were to try
> > following links because we're looking things up in a Git tree at a
> > particular commit and not on the filesystem.  A bigger concern would be
> > whether the internals of Git do anything bad (like invalid memory
> > access) if we give the tree traversal machinery a path that goes up out
> > of the repository; I doubt it but I have not checked.
> If we use url-rewrites (and let the http-client care about getting the
> correct file or directory), this would be a non-issue.

It could also mean that cross-repository symlinks work if the server
layout matches that that is expected for checkouts of the repositories.

But it's not exactly helpful if a repository contains an absolute
symlink and I don't think we want to start figuring out whether a
redirect makes sense - what do we do if we decide it doesn't?