cgit and symlinks

[i at monkz.de (MonkZ)]

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.

MfG
MonkZ

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