Re: Read only devices (Re: BoS: amodload.tar.gz - ...)

[gdonl () gv ssi1 com (Don Lewis)]

On Jun 20, 11:15pm, Matt Zimmerman wrote:
} Subject: Re: Read only devices (Re: BoS: amodload.tar.gz - ...)
} On Fri, 21 Jun 1996, Sean Vickery wrote:
}
} > Mounting filesystems containing system binaries read-only does not
} > sound as safe as turning on the hardware write-protect on the disks
} > containing those filesystems.
} >
} > Why? If an attacker can alter your system binaries, s/he must have root
} > privileges.  Which means s/he can also unmount the filesystems and
} > remount them read-write.  But to change the disk back to read-write
} > cannot be done over the network.  It requires physical access to the
} > disk(s).
}
} Right...which makes a good case for using NFS instead, and exporting the
} filesystems read-only from a server which is hopefully less accessible to
} the general public and/or intruders (offering a very limited set of
} network services, etc.).  Of course, then you have to deal with the usual
} NFS security issues (most of which can be avoided within reasonable limits
} by well-configured firewalls and TCP wrappers).

I don't think NFS can be made safe enough.  The intruder could inject
NFS responses onto the network that would substitute his own pieces
for pieces of the system binaries that you're trying to protect.  This
would be similar to the potential attack against the Netscape browser
cryptographic machinery that was reported a while back.  Even if the
network is secured and only contains the read-only NFS server and the
"diskless" client, if the attacker has root privileges on the client
and is able to gain access to something like NIT or BPF, the attack
could be carried out from the client machine.

                        ---  Truck