Does NFS support Linux Capabilities

[Chuck Lever III]

> On Sep 9, 2022, at 9:13 AM, J. Bruce Fields <bfields at fieldses.org> wrote:
> 
> On Fri, Sep 09, 2022 at 05:23:46AM -0400, Theodore Ts'o wrote:
>> On Thu, Sep 08, 2022 at 08:24:02PM +0000, Chuck Lever III wrote:
>>> Given these enormous challenges, who would be willing to pay for
>>> standardization and implementation? I'm not saying it can't or
>>> shouldn't be done, just that it would be a mighty heavy lift.
>>> But maybe other folks on the Cc: list have ideas that could
>>> make this easier than I believe it to be.
>> 
>> ... and this is why the C2 by '92 initiative was doomed to failure,
>> and why Posix.1e never completed the standardization process.  :-)
>> 
>> Honestly, capabilities are super coarse-grained, and I'm not sure they
>> are all that useful if we were create blank slate requirements for a
>> modern high-security system.  So I'm not convinced the costs are
>> sufficient to balance the benefits.
> 
> I seem to recall the immediate practical problem people have hit is that
> some rpms will fail if it can't set file capabilities.

Indeed, that is the most common reason for a request to implement
capabilities for NFS files.


> So in practice NFS may not work any more for root filesystems.

"may not work any more" -- well let's be precise. NFS works for root,
but doesn't support distributions that require file capabilities on
certain executables. Thus it cannot be used in those cases.


> Maybe there's some workaround.

The workaround I'm familiar with is to use a local filesystem that
implements extended attributes, but store it on network-attached
block storage (eg iSCSI).


> Taking a quick look at my laptop, there's not as many as I expected:
> 
> [root at parkour bfields]# getcap -r /usr
> /usr/bin/arping cap_net_raw=p
> /usr/bin/clockdiff cap_net_raw=p
> /usr/bin/dumpcap cap_net_admin,cap_net_raw=ep
> /usr/bin/newgidmap cap_setgid=ep
> /usr/bin/newuidmap cap_setuid=ep
> /usr/sbin/mtr-packet cap_net_raw=ep
> /usr/sbin/suexec cap_setgid,cap_setuid=ep

Yep, it's still a short list.


--
Chuck Lever