Messages in this thread | | | Subject | Re: [Question] mount points on knfsd. | Date | Thu, 10 Sep 1998 08:47:21 -0700 | From | "G. Allen Morris III" <> |
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Bill,
>>>Bill Hawes said: > > Returning the underlying directory avoids inode aliasing problems, but > is otherwise a security problem in that it exposes part of a filesystem > not otherwise visible. (How many sysadmins know what's below the > mountpoints for something that's routinely coverd?)
I think that the solution to this problem is to make sure the mount points are empty and unwritable. On ext2 filesystems the `i' flag can be set for the mount points to solve this security problem.
I really believe that this is the correct way to handle `covered' files. It gives the system administrator more flexability.
As an example: if computer A has /usr all on one partition Computer B mount A:/usr on /usr Computer A then mounts C:/usr/X11R6 on /usr/X11R6
What should a user on computer B see when they execute ls -la /usr/X11R6?
With this patch they will continue to see what they have always seen (A:/usr/X11R6).
With your idea they would see (I think) `.' and `..' and nothing else.
And then some would suggest that C:/usr/X11R6 should be displayed.
> This issue has come up several times before, and people have sent in > patches to let nfsd access the underlying directory. I don't think it's > a good thing to do though.
I hope I have convienced you ;-).
> What would be acceptable is to allow the mounted-over inode to be > visible, but nothing further, so that it could become a mountpoint but > not serve to access any normally invisible directories. >
Also, I think this would be hard!
--------------------------------- G. Allen Morris III
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