ceph: take a cred reference instead of tracking individual uid/gid

Replace req->r_uid/r_gid with an r_cred pointer and take a reference to
that at the point where we previously would sample the two.  Use that to
populate the uid and gid in the header and release the reference when
the request is freed.

This should enable us to later add support for sending supplementary
group lists in MDS requests.

[ idryomov: break unnecessarily long lines ]
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/mds_client.c

@@ -833,6 +833,7 @@ void ceph_mdsc_release_request(struct kref *kref)
 	}
 	kfree(req->r_path1);
 	kfree(req->r_path2);
+	put_cred(req->r_cred);
 	if (req->r_pagelist)
 		ceph_pagelist_release(req->r_pagelist);
 	put_request_session(req);
@@ -888,8 +889,7 @@ static void __register_request(struct ceph_mds_client *mdsc,
 	ceph_mdsc_get_request(req);
 	insert_request(&mdsc->request_tree, req);
 
-	req->r_uid = current_fsuid();
-	req->r_gid = current_fsgid();
+	req->r_cred = get_current_cred();
 
 	if (mdsc->oldest_tid == 0 && req->r_op != CEPH_MDS_OP_SETFILELOCK)
 		mdsc->oldest_tid = req->r_tid;
@@ -2542,8 +2542,10 @@ static struct ceph_msg *create_request_message(struct ceph_mds_client *mdsc,
 
 	head->mdsmap_epoch = cpu_to_le32(mdsc->mdsmap->m_epoch);
 	head->op = cpu_to_le32(req->r_op);
-	head->caller_uid = cpu_to_le32(from_kuid(&init_user_ns, req->r_uid));
-	head->caller_gid = cpu_to_le32(from_kgid(&init_user_ns, req->r_gid));
+	head->caller_uid = cpu_to_le32(from_kuid(&init_user_ns,
+						 req->r_cred->fsuid));
+	head->caller_gid = cpu_to_le32(from_kgid(&init_user_ns,
+						 req->r_cred->fsgid));
 	head->ino = cpu_to_le64(req->r_deleg_ino);
 	head->args = req->r_args;
 

fs/ceph/mds_client.h

@@ -275,8 +275,7 @@ struct ceph_mds_request {
 
 	union ceph_mds_request_args r_args;
 	int r_fmode;        /* file mode, if expecting cap */
-	kuid_t r_uid;
-	kgid_t r_gid;
+	const struct cred *r_cred;
 	int r_request_release_offset;
 	struct timespec64 r_stamp;