122 lines
3.6 KiB
Go
122 lines
3.6 KiB
Go
// Copyright 2018 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package auth
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import (
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"math"
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)
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// UID is a user ID in an unspecified user namespace.
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type UID uint32
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// GID is a group ID in an unspecified user namespace.
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type GID uint32
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// In the root user namespace, user/group IDs have a 1-to-1 relationship with
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// the users/groups they represent. In other user namespaces, this is not the
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// case; for example, two different unmapped users may both "have" the overflow
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// UID. This means that it is generally only valid to compare user and group
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// IDs in the root user namespace. We assign distinct types, KUID/KGID, to such
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// IDs to emphasize this distinction. ("k" is for "key", as in "unique key".
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// Linux also uses the prefix "k", but I think they mean "kernel".)
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// KUID is a user ID in the root user namespace.
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type KUID uint32
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// KGID is a group ID in the root user namespace.
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type KGID uint32
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const (
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// NoID is uint32(-1). -1 is consistently used as a special value, in Linux
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// and by extension in the auth package, to mean "no ID":
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//
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// - ID mapping returns -1 if the ID is not mapped.
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//
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// - Most set*id() syscalls accept -1 to mean "do not change this ID".
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NoID = math.MaxUint32
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// OverflowUID is the default value of /proc/sys/kernel/overflowuid. The
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// "overflow UID" is usually [1] used when translating a user ID between
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// namespaces fails because the ID is not mapped. (We don't implement this
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// file, so the overflow UID is constant.)
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//
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// [1] "There is one notable case where unmapped user and group IDs are not
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// converted to the corresponding overflow ID value. When viewing a uid_map
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// or gid_map file in which there is no mapping for the second field, that
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// field is displayed as 4294967295 (-1 as an unsigned integer);" -
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// user_namespaces(7)
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OverflowUID = UID(65534)
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OverflowGID = GID(65534)
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// NobodyKUID is the user ID usually reserved for the least privileged user
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// "nobody".
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NobodyKUID = KUID(65534)
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NobodyKGID = KGID(65534)
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// RootKUID is the user ID usually used for the most privileged user "root".
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RootKUID = KUID(0)
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RootKGID = KGID(0)
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RootUID = UID(0)
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RootGID = GID(0)
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)
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// Ok returns true if uid is not -1.
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func (uid UID) Ok() bool {
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return uid != NoID
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}
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// Ok returns true if gid is not -1.
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func (gid GID) Ok() bool {
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return gid != NoID
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}
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// Ok returns true if kuid is not -1.
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func (kuid KUID) Ok() bool {
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return kuid != NoID
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}
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// Ok returns true if kgid is not -1.
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func (kgid KGID) Ok() bool {
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return kgid != NoID
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}
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// OrOverflow returns uid if it is valid and the overflow UID otherwise.
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func (uid UID) OrOverflow() UID {
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if uid.Ok() {
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return uid
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}
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return OverflowUID
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}
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// OrOverflow returns gid if it is valid and the overflow GID otherwise.
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func (gid GID) OrOverflow() GID {
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if gid.Ok() {
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return gid
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}
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return OverflowGID
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}
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// In translates kuid into user namespace ns. If kuid is not mapped in ns, In
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// returns NoID.
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func (kuid KUID) In(ns *UserNamespace) UID {
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return ns.MapFromKUID(kuid)
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}
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// In translates kgid into user namespace ns. If kgid is not mapped in ns, In
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// returns NoID.
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func (kgid KGID) In(ns *UserNamespace) GID {
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return ns.MapFromKGID(kgid)
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}
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