Re: Possible issue with linux xattr support?

* Dmitry Chagin <dchagin@freebsd.org> [20230829 17:45]:
> On Tue, Aug 29, 2023 at 12:59:11PM +0200, Felix Palmen wrote:
> > 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 :)

Sure, poudriere is running all builds as "nobody" by default.

> > 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

Ok, I did some tests in a poudriere jail using Linux bash, as root.
First, with only the first patch:

| bash-5.2# getfattr -d /bin/sh
| getfattr: /bin/sh: Operation not supported
| bash-5.2# setfattr -n user.foo -v bar /bin/sh
| bash-5.2# getfattr -n user.foo /bin/sh
| getfattr: Removing leading '/' from absolute path names
| # file: bin/sh
| user.foo="bar"
| bash-5.2# setfattr -x user.foo /bin/sh
| bash-5.2# setfattr -x system.foo /bin/sh
| setfattr: /bin/sh: Operation not supported

So, using user.* works, using system.* doesn't, and maybe a bit
surprising(?), dumping all attributes which by default excludes the
system namespace doesn't work either.

Then with the second patch applied as well:

| bash-5.2# getfattr -d /bin/sh
| bash-5.2# setfattr -n system.foo -v bar /bin/sh
| bash-5.2# getfattr -d /bin/sh -m-
| getfattr: Removing leading '/' from absolute path names
| # file: bin/sh
| system.foo="bar"
| 
| bash-5.2# setfattr -x system.foo /bin/sh
| bash-5.2# getfattr -d /bin/sh -m-
| bash-5.2#

This looks perfectly fine, thanks a lot!

I still wonder, is the first patch needed anyways? Maybe I fail to
understand something here. Won't it map *every* EPERM to ENOSUP and
can't this be an issue?

Cheers, Felix

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