Re: Possible issue with linux xattr support?

On 8/29/23 14:02, Shawn Webb wrote:
> On Tue, Aug 29, 2023 at 05:45:51PM +0300, Dmitry Chagin wrote:
>> On Tue, Aug 29, 2023 at 12:59:11PM +0200, Felix Palmen wrote:
>>> * Dmitry Chagin <dchagin@freebsd.org> [20230828 18:57]:
>>>> On Mon, Aug 28, 2023 at 08:03:33AM +0200, Felix Palmen wrote:
>>>>> * Cy Schubert <Cy.Schubert@cschubert.com> [20230827 16:59]:
>>>>>>
>>>>>> If we are to break it to fix a problem, maybe a sysctl to enable/disable then?
>>>>>
>>>>> IMHO depends on the exact nature of the problem. If it's confirmed that
>>>>> it (always and only) breaks for jailed processes, just disabling it for
>>>>> them would be the better workaround. "No-op" calls won't break anything.
>>>>>
>>>>
>>>> please, try: https://people.freebsd.org/~dchagin/xattrerror.patch
>>>
>>> Thanks, I can confirm this avoids the issue in both cases I experienced
>>> (install from GNU coreutils and python).
>>>
>> thanks, this is the first half of the fix, it works for you due to you
>> are running tools under unprivileged user, afaiu. The second I have
>> tested by myself :)
>>
>>> If I understand this patch correctly, it completely avoids EPERM,
>>> masking it as not supported, so callers should consider it non-fatal,
>>> allowing to silently ignore writing of "system" attributes while still
>>> keeping other functionality?
>>>
>> system namespace is accessible only for privileged user, for others Linux
>> returns ENOTSUP. So many tools ignores this error, eg ls.
>>
>> the second: https://people.freebsd.org/~dchagin/sea_jailed.patch
>>
>> Try this under privileged user, please.
> 
> Back in 2019, I had a similar issue: I needed access to be able to
> read/write to the system extended attribute namespace from within a
> jailed context. I wrote a rather simple patch that provides that
> support on a per-jail basis:
> 
> https://git.hardenedbsd.org/hardenedbsd/HardenedBSD/-/commit/96c85982b45e44a6105664c7068a92d0a61da2a3
> 
> Hopefully that's useful to someone.
> 
> Thanks,
> 

FWIW (which likely isn't much), I like this approach much better; it 
makes more sense to me that it's a feature controlled by the creator of 
the jail and not one allowed just by using a compat ABI within a jail.

Thanks,

Kyle Evans