rm(1) bug, possibly serious

[Mark Andrews]

> On Tue, 25 Sep 2007, LI Xin wrote:
>  > Oliver Fromme wrote:
>  > > Nicolas Rachinsky wrote:
>  > >  > Oliver Fromme wrote:
>  > >  > > By the way, an additional confusion is that ".." and "../"
>  > >  > > are handled differently.  Specifying ".." always leads to
>  > >  > > this message:
>  > >  > > 
>  > >  > > rm: "." and ".." may not be removed
>  > >  > > 
>  > >  > > and nothing is actually removed.  It is confusing that
>  > >  > > adding a slash leads to a different error message _and_
>  > >  > > removal of the contents of the parent directory.  Clearly
>  > >  > > a POLA violation.
> 
> Clearly a bug, and well spotted, especially if as old as reported.
> 
>  > >  > 
>  > >  > Adding a slash often leads to different behaviour.
>  > > 
>  > > Yes, I'm aware of that.  I often make use of the feature
>  > > that "find /sys/" expands the symlink, while "find /sys"
>  > > does not.  The same holds true for ls(1).
> 
> But fortunately not for rm(1):
> 
>      The rm utility removes symbolic links, not the files referenced by the
>      links.
> 
>      It is an error to attempt to remove the files /, . or ..
> 
>  > > However, I would still argue that there is no sane reason
>  > > for "rm -rf ../" behaving differently from "rm -rf ..",
>  > > especially because it behaves differently in a destructive
>  > > way.  That's why I call it a POLA violation.
>  > 
>  > Also a POSIX violation IMHO :-)
> 
> Indeed; I can't imagine a situation where removing "." (let alone "..") 
> and so orphaning the pwd might be considered sane, never mind legal .. 
> but maybe I lack imagination :) 

	You lack imagination.

	When you found the directory you want to remove and you are
	in it it is much less error prone to remove "." recursively
	that to go up one directory and try to find the directory
	you were just in.

	The the prohibitions comes from when you literally removed
	directories by unlinking the directory and "." and ".."
	within the directory in user space.  It was easy to stuff
	up a directory structure.

	Mark
 
> Cheers, Ian
> 
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org