Path: utzoo!attcan!uunet!husc6!uwvax!tank!uxc!ksuvax1!tar
From: tar@ksuvax1.cis.ksu.edu (Tim Ramsey)
Newsgroups: comp.unix.questions
Subject: Re: PWD gives getwd: couldn't open .. on world r-x root directories
Message-ID: <1181@ksuvax1.cis.ksu.edu>
Date: 6 Nov 88 10:03:05 GMT
References: <1590@sun.soe.clarkson.edu> <1165@ksuvax1.cis.ksu.edu> <1971@cbnews.ATT.COM>
Reply-To: tar@ksuvax1.cis.ksu.edu (Tim Ramsey)
Distribution: na
Organization: Kansas State University, Dept of Computing & Information Sciences
Lines: 39

In article <1165@ksuvax1.cis.ksu.edu> I write:
>It seems odd that the permissions of the mount point affect access to the
>mounted file system.  Is this a bug or feature?

In article <1971@cbnews.ATT.COM> lvc@cbnews.ATT.COM (Lawrence V. Cipriani) writes:
>This is a feature.  The permissions of the mount point determine the permission
>of the directory after the mount.  The permission on the raw disk only control
>access to that disk device as if it was a file.

I think you are referring to the special file in /dev.  I was commenting on
the mount point and the filesystem root directory.

To add to the confusion (this is 4.3BSD):

% ls -ld /mnt
drwxr-xr-x  7 root          512 Aug  7 23:47 /mnt
% umount /mnt
% ls -ld /mnt
drwxr-xr-x  2 root          512 Jan 88 09:12 /mnt
% chmod 000 /mnt
% ls -ld /mnt
d---------  2 root          512 Jan 88 09:12 /mnt
% mount /mnt
% ls -ld /mnt
drwxr-xr-x  2 root          512 Jan 88 09:12 /mnt

The root directory of the mounted filesystem "hides" the mount directory.
So you don't see the 000 permissions.  I spent a goodly amount of time looking
for the problem the first time I ran into this.

It appears that access checks are done for both the mount directory and the
file system root directory.  You have to pass both to read/write/execute.
I dunno, but this seems like a bug.

-- 
Timothy Ramsey, USENET Keeper-Upper  | Ada:
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