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lynx-dev a word from on high
From: |
Philip Webb |
Subject: |
lynx-dev a word from on high |
Date: |
Sat, 10 Oct 1998 15:25:59 -0400 (EDT) |
981009 NHE & TD commented on our system security:
>>> ls -ld /homefs/u7/purslow gives:
>>>
>>> drwx--x--x 9 purslow user 512 Oct 9 07:53 /homefs/u7/purslow
>> ^ ^
>> As an amateur, I find this curious. I have always made permissions
>> on private accounts 700. With a setup like this, couldn't a person
>> logged on to that system exec any of the programs under that directory,
>> e.g., run the private image of lynx within that directory?
> yes - IF they know where it is.
the CHASS sysadmin has replied to my questions very promptly:
(1) why are user home directories world-executable?
reply> A directory being world executable does not mean that programs
> in that directory (or its subdirectories) can be executed by others.
> Access to files (incl programs) is governed by their own set of permissions.
> It may sound a bit confusing, but world executable directories are needed
> solely to gain access to directories (not to files in those directories).
> Now, if you have your web site on ~purslow , that translates
> to /homes/purslow/public_html : without /homes/purslow being
> world executable, nobody would be able to access your personal web pages.
> Within /homes/purslow you can create any number of subdirectories
> as 700 (ie rwx------ ), and nobody will have access to them.
> Even within the home directories, your files can be made 600 or 700
> (ie rw------- or rwx------ ) & again nobody will be able to access them.
(2) why is /homes/purslow a symbolic link (i knew this one already)?
> Every user has a home directory on a file system, in your case /homefs/u7
> Because there are many such file systems on many physical disks
> (and some file systems even span more than one physical disk),
> the standard way of expressing a home directory is by /homes/userid ,
> which means every user is listed in /homes , from which a symbolic link
> points to the actual file system where that home directory is mounted.
> This way we can move disks around, create & delete various file systems etc
> & users will still be able to refer to their home directories
> in a constant manner (ie via /homes/userid ).
(3) why is there a link-to-a-link?
> Oh, but this should be absolutely irrelevant to any program accessing
> your home directory as /homes/purslow. Symbolic links are resolved
> internally by the operating system (NOT by the application).
> /homes could have been put anywhere, depending on where we had disk space
> during various reorganizations of file systems. The whole idea
> of a logical home directory is to isolate users from this kind
> of dependencies. I can't think of a program that would have problems
> with symbolic links.
>
> To specifically answer your question, consider a situation when you are
> rebuilding the root directory ( / ), but don't want users to be affected.
> /homes is made to point elsewhere (eg to /var file system),
> where user home directories are placed, many of them actually dispersed
> accross other file systems (thus the second link). Still, I don't see
> why such things should be of any interest to you (or any other user).
> It's like asking how Canada Post maps your postal code to actual address:
> whether they go through "one link" or many, should be absolutely irrelevant
> to you as long as your letters are delivered.
so where's the potential security hole i'm being protected against
by the piece of programming which prevented my saving .lynxrc ?
--
========================,,============================================
SUPPORT ___________//___, Philip Webb : address@hidden
ELECTRIC /] [] [] [] [] []| Centre for Urban & Community Studies
TRANSIT `-O----------O---' University of Toronto
- Re: lynx-dev Re: who owns what, (continued)
Re: lynx-dev Re: who owns what, Philip Webb, 1998/10/09
Re: lynx-dev Re: who owns what, dickey, 1998/10/09
Re: lynx-dev Re: who owns what, Nelson Henry Eric, 1998/10/09
Re: lynx-dev Re: who owns what, dickey, 1998/10/09
Re: lynx-dev Re: who owns what, Nelson Henry Eric, 1998/10/09
Re: lynx-dev Re: who owns what, Leonid Pauzner, 1998/10/10
Re: lynx-dev Re: who owns what, Bela Lubkin, 1998/10/10
Re: lynx-dev Re: who owns what, David Combs, 1998/10/10
Re: lynx-dev Re: who owns what, Bela Lubkin, 1998/10/11