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SubjectRe: autofs vs. Sun automount -- new fs proposal
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Richard Gooch writes ("Re: autofs vs. Sun automount -- new fs proposal"):
> Peter Benie writes:
> > Richard Gooch writes ("Re: autofs vs. Sun automount -- new fs proposal"):
> > > Peter Benie writes:
> > > > I don't actually see the point of implementing a read-only loopback
> > > I guess you never notice the CERT security notices, then?
> >
> > Are you suggesting that on Linux, one user can write to another's
> > files? (I'm assuming that people aren't stupid enough to have world
> > writable files etc.) If so, that's a bug that should be fixed.
>
> I'm pointing out that network servers are commonly attacked because
> they have bugs in them. Some of these bugs allow crackers to write
> files they shouldn't.

If the server is running as one uid, and the file is owned by a
different uid, then no amount of cracking will allow the server to
write to the file (at least, not directly).
A server might write to the file indirectly by exploiting bugs in
privileged programs on the same machine. Chroot guards against most of
those attacks.

> Sometimes network servers have to run as root.

For most network servers, the part that must run as root is very
small. Many servers are misdesigned and run all their code as root,
but read-only lofs is not a quick fix for that problem.

> One of the most common bugs I see in CERT announcements is that some
> or other server isn't preventing unauthorised writing to some file. A
> read-only lofs offers strong protection against that.

root can change the mount options for the loopback mount, or it can
access /root/.rhosts, /etc/shadow etc. without going through the
loopback mount. read-only loopback mounts offer no protection from
programs running as root.

Do you have any real applications for read-only loopback mounts that
cannot be solved using conventional, portable techniques?

Peter

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