We also have a way of achieving this in ganesha with the help of “is_superuser” FSAL API.

- Sriram

From: Frank Filz <ffilzlnx@mindspring.com>
Date: Wednesday, March 11, 2020 at 9:45 AM
To: Deepthi Shivaramu <des@vmware.com>, "devel@lists.nfs-ganesha.org" <devel@lists.nfs-ganesha.org>
Subject: [NFS-Ganesha-Devel] Re: chown on a file with 777 permission does not work for any non-root user, not even the owner of the file

Is there some documentation on how this works on other servers you can point us to? I wasn’t aware this was allowed outside the context of ACLs, though obviously if you can allow the action with ACLs, there might be a case for allowing it otherwise, though ACLs allow it on a per-file basis (and Windows only allows an administrator to set “take ownership” flag on a file so the user can take ownership of a file as opposed to the administrator changing the ownership).

Frank

From: Deepthi Shivaramu [mailto:des@vmware.com]
Sent: Wednesday, March 11, 2020 8:08 AM
To: Frank Filz <ffilzlnx@mindspring.com>; devel@lists.nfs-ganesha.org
Subject: [NFS-Ganesha-Devel] Re: chown on a file with 777 permission does not work for any non-root user, not even the owner of the file

Frank,

Thanks for the reply. I got your point.

Most of the enterprise NFS servers provide a hook to allow chown by non root users. Can we implement a hook which when set allow NFSv3 setattr by non root to change owner of the file when file has write permission. ACLs are anyway a solution with NFSv4.

regards,

Deepthi

On 11 Mar 2020 19:55, Frank Filz <ffilzlnx@mindspring.com> wrote:

> I have NFSv3 mount on linux client and trying to change the owner of the file:
>
> [root@sc-rdops-vm07-dhcp-212-202 mnt]# ls -la new.txt -rwxrwxrwx. 1 testu2
> testg2 7 Mar 11 04:00 new.txt
> [root@sc-rdops-vm07-dhcp-212-202 mnt]# su testu2
> [testu2@sc-rdops-vm07-dhcp-212-202 mnt]$ id
> uid=2222(testu2) gid=8888(testg2) groups=8888(testg2)
> [testu2@sc-rdops-vm07-dhcp-212-202 mnt]$
> [testu2@sc-rdops-vm07-dhcp-212-202 mnt]$ chown testu1 new.txt
> chown: changing ownership of ‘new.txt’: Operation not permitted
> [testu2@sc-rdops-vm07-dhcp-212-202 mnt]$
> [root@sc-rdops-vm07-dhcp-212-202 mnt]# su testu1
> [testu1@sc-rdops-vm07-dhcp-212-202 mnt]$ id
> uid=1111(testu1) gid=8888(testg2) groups=8888(testg2)
> [testu1@sc-rdops-vm07-dhcp-212-202 mnt]$
> [testu1@sc-rdops-vm07-dhcp-212-202 mnt]$ chown testu1 new.txt
> chown: changing ownership of ‘new.txt’: Operation not permitted
> [testu1@sc-rdops-vm07-dhcp-212-202 mnt]$
>
> The file belongs to testu2 and when I try to change the owner to testu1 logged
> in as testu2, it hits this error :
>
> 2020-03-11T11:12:08Z : epoch 5e5f8af3 : vdfsops0aa0d27c.vsanfs-sh.prv :
> ganesha.nfsd-50332[::ffff:10.160.212.202] [svc_46] 354
> :fsal_check_setattr_perms :FSAL :Access check returned Forbidden action (new
> OWNER was not user)
>
>         if (FSAL_TEST_MASK(attr->valid_mask, ATTR_OWNER)) {
>                 /* non-root is only allowed to "take ownership of file" */ .    <--- It says
> owner of file cannot change the ownership to someone else. Someone else
> needs to take ownership.
>                 if (attr->owner != creds->caller_uid) {
>                         status = fsalstat(ERR_FSAL_PERM, 0);
>                         note = " (new OWNER was not user)";
>                         goto out;
>                 }
>
>
> So I login as non-owner, testu1 and try chown, it proceeds from this check but
> fails here:
>
> 2020-03-11T11:11:01Z : epoch 5e5f8af3 : vdfsops0aa0d27c.vsanfs-sh.prv :
> ganesha.nfsd-50332[::ffff:10.160.212.202] [svc_41] 354
> :fsal_check_setattr_perms :FSAL :Access check returned Forbidden action (no
> ACL to check)
>
>        if (current->acl) {
>                 status = obj->obj_ops->test_access(obj, access_check, NULL,
>                                                   NULL, false);
>                 note = " (checked ACL)";
>                 goto out;
>         }
>
>         if (access_check != FSAL_ACE4_MASK_SET(FSAL_ACE_PERM_WRITE_DATA))
> {
>                 /* Without an ACL, this user is not allowed some operation */
>                 status = fsalstat(ERR_FSAL_PERM, 0);
>                 note = " (no ACL to check)";
>                 goto out;
>         }
>
> access_check variable starts with 0 and we put in only
> FSAL_ACE_PERM_WRITE_OWNER in first block for chown case. So obviously it
> does not contain FSAL_ACE_PERM_WRITE_DATA which we are checking here.
> So how do we expect this to proceed? We do not support ACLs yet and anyway
> this is NFSv3 case, I believe we should not have any dependency on ACL support
> for this usecase.

In POSIX systems, only root can change ownership of files (and owner of a file may change the group owner of the file to one of that user's groups). Of course in Linux a non-root user MIGHT be given a CAP to allow it to change ownership, but NFS is not really set up to deal with CAPs.

Only with NFSv4 ACLs or RichACLs are non-root users allowed to change ownership of files.

Frank