From: Pixel <pixel@...>
Date: 2002-03-13T20:04:38+09:00
Subject: Re: Some potential RCRs

"Guy N. Hurst" <gnhurst@hurstlinks.com> writes:

> Bob Alexander wrote:
> > 
> > On the topic of whether ".." and "." should be in our directory
> > listings:
> > [...]
> > Can someone suggest an argument as to why having them in the listed
> > entries is useful?
> 
> I often use ls -al in the shell because I also need to see the 
> permissions and/or owner of '.'
> And it is useful in the shell to use '..' as a navigation tool.

be aware that most shells trick on you about '..' [1]:

% mkdir -p dir1/dir2
% ln -s dir1/dir2 link1
% cd link1
% pwd
/tmp/link1

% ls ..
dir2
% (cd .. ; ls)
dir1

% cd ..
% pwd        # should be /tmp/dir1
/tmp


Another extreme argument against the use of ".." is [2]:

# An insecure chdir("..") syscall is done after removing content of a
# subdirectory in order to get back to the upper directory during recursive
# removal of directory tree.
#
# Example of 'rm -fr /tmp/a' removing '/tmp/a/b/c' directory tree:
# 
# (strace output simplified for better readability)
# 
# chdir("/tmp/a")                         = 0
# chdir("b")                              = 0
# chdir("c")                              = 0
# chdir("..")                             = 0
# rmdir("c")                              = 0
# chdir("..")                             = 0
# rmdir("b")                              = 0
# fchdir(3)                               = 0
# rmdir("/tmp/a")                         = 0
# 
# After current directory is changed to /tmp/a/b/c a race condition occurs.
# If we then move /tmp/a/b/c directory to the /tmp/c two subsequent
# chdir("..") syscalls will move to the root directory / and rm will start
# removing files from the whole file systems if it has enough privileges
# (i.e. if called by root user).


> But when I programmatically iterate over directory entries,
> I don't care about '.' or '..'

agreed. get rid of '.' and '..' !!


[1] bash, zsh and pdksh do not really use chdir("..") when asked "cd .."
    tcsh, sash do really use chdir("..") when asked "cd .."

[2] http://online.securityfocus.com/archive/1/260936