Mounting floppies

[Brandon S. Allbery]

As quoted from <404 at hropus.UUCP> by jgy at hropus.UUCP (John Young):
+---------------
| > (I [allbery at ncoast) suggest a secure user floppy mounter)
| 
| No, you cannot rely on a system which attempts to stop bad things
| from being done to removable media, the effort should on defending
| against pressumed bad media.
| Therefore you still need your suid (sgid might be better?)
| mount command to check for s(uid|gid)
| programs and either clear them or refuse to mount.
+---------------

This can be done as well; after all, a linear pass through a floppy's ilist
doesn't take very long... and you *do* have a point, since someone could
build a floppy on an unprotected system and set the proper flags on it, etc.
(A mountable user floppy doesn't need suid/sgid files anyway.  Special files
(i.e. character or block devices, but not necessarily FIFOs or Xenix name
files, etc. [and do BSD AF_UNIX sockets bind()'ed to filenames still work
after the last close on the socket?]) would probably cause a refusal to
mount, since otherwise the mount utility needs to know quite a bit more
about the filesystem.

Now that I think about it, both conditions (my non-modifiability and your
security checking) are necessary, but neither is sufficient by itself.
--Query:  do we need to avoid symlinks as well?  From what I know about
them, it might not be necessary because they can't grant access to otherwise
protected files, but....

BTW, sgid won't work in this case; the kernel returns EPERM if anyone except
root tries to do a mount().

Maybe I'll whip up such a program.  Won't do much for ncoast (no
floppies...) but might be useful on the job.

++Brandon
-- 
Brandon S. Allbery, comp.sources.misc moderator and one admin of ncoast PA UN*X
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