full-disclosure - Re: Possibility to exploit bash "*" processing

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Message-ID: <10170.1316543488@turing-police.cc.vt.edu>
Date: Tue, 20 Sep 2011 14:31:28 -0400
From: Valdis.Kletnieks@...edu
To: Kirils Solovjovs <kirils.solovjovs@...ils.com>
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: Possibility to exploit bash "*" processing

On Tue, 20 Sep 2011 13:29:11 +0300, Kirils Solovjovs said:
> Brought this up a year ago. Seems that no attention has been given to
> this so far.

Probably because anybody who's used the various Bourne-style shells for a while
considers it a feature, not a bug.  This is a case where the Principle of Least
Surprise comes up with different answers for novice users and for experts:
"What? A * can expand into an unintended command argument?" "Yeah, what *else*
would it do - the shell is just globbing, it doesn't know for sure what the
command will do with the parameter".

Multics had an alternate solution for this issue - when you issued a command,
it would get invoked right then and there and take over terminal input and
allow guided completions knowing what the command syntax was (think "love child
of getopt and readline" ;) Of course, this doesn't play well with pipes,
especially if the pipe further down the line has a redirection that fails. 

> One solution would be to modify "*" processing so that it ignores
> filenames that start "-" similarly as it ignores filenames that start
> with "."'

No, you don't want to do that.  You want to provide an *optional*
flag, similar to the shopt settings for 'dotglob', 'extglob', 'failglob', 'globstar',
'nocaseglob', and 'nullglob'.

Having said that, a 'shopt dashglob' shouldn't be too hard to implement,
as you can do 98% of it based on the already-existing 'dotglob' code, and
that's probably the way to address the issue.

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