Re: [PATCH v2 1/1] xattr: Allow user.* xattr on symlink and special files

From: Vivek Goyal
Date: Mon Jul 12 2021 - 10:03:10 EST


On Fri, Jul 09, 2021 at 04:10:16PM -0400, Bruce Fields wrote:
> On Fri, Jul 9, 2021 at 1:59 PM Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> > nfs seems to have some issues.
>
> I'm not sure what the expected behavior is for nfs. All I have for
> now is some generic troubleshooting ideas, sorry:
>
> > - I can set user.foo xattr on symlink and query it back using xattr name.
> >
> > getfattr -h -n user.foo foo-link.txt
> >
> > But when I try to dump all xattrs on this file, user.foo is being
> > filtered out it looks like. Not sure why.
>
> Logging into the server and seeing what's set there could help confirm
> whether it's the client or server that's at fault. (Or watching the
> traffic in wireshark; there are GET/SET/LISTXATTR ops that should be
> easy to spot.)
>
> > - I can't set "user.foo" xattr on a device node on nfs and I get
> > "Permission denied". I am assuming nfs server is returning this.
>
> Wireshark should tell you whether it's the server or client doing that.
>
> The RFC is https://datatracker.ietf.org/doc/html/rfc8276, and I don't
> see any explicit statement about what the server should do in the case
> of symlinks or device nodes, but I do see "Any regular file or
> directory may have a set of extended attributes", so that was clearly
> the assumption. Also, NFS4ERR_WRONG_TYPE is listed as a possible
> error return for the xattr ops. But on a quick skim I don't see any
> explicit checks in the nfsd code, so I *think* it's just relying on
> the vfs for any file type checks.

Hi Bruce,

Thanks for the response. I am just trying to do set a user.foo xattr on
a device node on nfs.

setfattr -n "user.foo" -v "bar" /mnt/nfs/test-dev

and I get -EACCESS.

I put some printk() statements and EACCESS is being returned from here.

nfs4_xattr_set_nfs4_user() {
if (!nfs_access_get_cached(inode, current_cred(), &cache, true)) {
if (!(cache.mask & NFS_ACCESS_XAWRITE)) {
return -EACCES;
}
}
}

Value of cache.mask=0xd at the time of error.

Thanks
Vivek