rm -r fails to delete entire hierarchy when path goes in and out of it

[Joshua Judson Rosen]

On 2014-09-17 12:52, Cathey, Jim wrote:
> Pretty sure 'our' upstream rm (in a prior life) expressly
> prohibited -r on starting paths that contained .. members.
> Too many weirdo cases where you would get into trouble.

GNU rm opens the top-level directory and uses unlinkat(), fstatat(), etc. to remove
files and subdirectories without having to resolve the paths for every
file/directory processed; so it runs into the problem (that some ".." link no
longer exists) only when it finally reaches that top-level directory.
It still refuses to operate on paths that _end_ in "/.." (or "/.").

I wonder if there's a reason it doesn't go one step further--get dirname()
of the top-level path, open _that_, and then use openat() on the _basename_--
to avoid having to re-resolve the path even when finally removing the top-level dir.

It's not obvious to me at a glance; there's a quite lot of code in there.

-- 
"'tis an ill wind that blows no minds."

> -----Original Message-----
> From: busybox [mailto:busybox-bounces at busybox.net] On Behalf Of Ralf Friedl
> Sent: Wednesday, September 17, 2014 2:02 AM
> To: Gian Ntzik; busybox at busybox.net
> Subject: Re: rm -r fails to delete entire hierarchy when path goes in and out of it
>
> Gian Ntzik wrote:
>> It seems that using rm -r with a path that goes into the hierarchy
>> intended for removal (and back up e.g. using dot-dots) fails to remove
>> the entire hierarchy.
>>
>> For example,
>>
>> $ mkdir -p /tmp/a/b/c
>> $ mkdir -p /tmp/a/e
>> $ rm -r /tmp/a/b/../../a
>> rm: can't remove 'a/b/../../a/e': No such file or directory
>> rm: can't remove 'a/b/../../a': No such file or directory
> GNU rm does this:
> $ mkdir -p /tmp/a/b/c /tmp/a/e
> $ rm -r /tmp/a/b/../../a
> rm: cannot remove '/tmp/a/b/../../a': No such file or directory
>
> In general I think it is not a good idea to pass such arguments to rm.