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// Copyright 2018 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package auth
import (
"gvisor.googlesource.com/gvisor/pkg/abi/linux"
"gvisor.googlesource.com/gvisor/pkg/syserror"
)
// Credentials contains information required to authorize privileged operations
// in a user namespace.
//
// +stateify savable
type Credentials struct {
// Real/effective/saved user/group IDs in the root user namespace. None of
// these should ever be NoID.
RealKUID KUID
EffectiveKUID KUID
SavedKUID KUID
RealKGID KGID
EffectiveKGID KGID
SavedKGID KGID
// Filesystem user/group IDs are not implemented. "... setfsuid() is
// nowadays unneeded and should be avoided in new applications (likewise
// for setfsgid(2))." - setfsuid(2)
// Supplementary groups used by set/getgroups.
//
// ExtraKGIDs slices are immutable, allowing multiple Credentials with the
// same ExtraKGIDs to share the same slice.
ExtraKGIDs []KGID
// The capability sets applicable to this set of credentials.
PermittedCaps CapabilitySet
InheritableCaps CapabilitySet
EffectiveCaps CapabilitySet
BoundingCaps CapabilitySet
// Ambient capabilities are not introduced until Linux 4.3.
// KeepCaps is the flag for PR_SET_KEEPCAPS which allow capabilities to be
// maintained after a switch from root user to non-root user via setuid().
KeepCaps bool
// The user namespace associated with the owner of the credentials.
UserNamespace *UserNamespace
}
// NewAnonymousCredentials returns a set of credentials with no capabilities in
// any user namespace.
func NewAnonymousCredentials() *Credentials {
// Create a new root user namespace. Since the new namespace's owner is
// KUID 0 and the returned credentials have non-zero KUID/KGID, the
// returned credentials do not have any capabilities in the new namespace.
// Since the new namespace is not part of any existing user namespace
// hierarchy, the returned credentials do not have any capabilities in any
// other namespace.
return &Credentials{
RealKUID: NobodyKUID,
EffectiveKUID: NobodyKUID,
SavedKUID: NobodyKUID,
RealKGID: NobodyKGID,
EffectiveKGID: NobodyKGID,
SavedKGID: NobodyKGID,
UserNamespace: NewRootUserNamespace(),
}
}
// NewRootCredentials returns a set of credentials with KUID and KGID 0 (i.e.
// global root) in user namespace ns.
func NewRootCredentials(ns *UserNamespace) *Credentials {
// I can't find documentation for this anywhere, but it's correct for the
// inheritable capability set to be initially empty (the capabilities test
// checks for this property).
return &Credentials{
RealKUID: RootKUID,
EffectiveKUID: RootKUID,
SavedKUID: RootKUID,
RealKGID: RootKGID,
EffectiveKGID: RootKGID,
SavedKGID: RootKGID,
PermittedCaps: AllCapabilities,
EffectiveCaps: AllCapabilities,
BoundingCaps: AllCapabilities,
UserNamespace: ns,
}
}
// NewUserCredentials returns a set of credentials based on the given UID, GIDs,
// and capabilities in a given namespace. If all arguments are their zero
// values, this returns the same credentials as NewRootCredentials.
func NewUserCredentials(kuid KUID, kgid KGID, extraKGIDs []KGID, capabilities *TaskCapabilities, ns *UserNamespace) *Credentials {
creds := NewRootCredentials(ns)
// Set the UID.
uid := kuid
creds.RealKUID = uid
creds.EffectiveKUID = uid
creds.SavedKUID = uid
// Set GID.
gid := kgid
creds.RealKGID = gid
creds.EffectiveKGID = gid
creds.SavedKGID = gid
// Set additional GIDs.
creds.ExtraKGIDs = append(creds.ExtraKGIDs, extraKGIDs...)
// Set capabilities.
if capabilities != nil {
creds.PermittedCaps = capabilities.PermittedCaps
creds.EffectiveCaps = capabilities.EffectiveCaps
creds.BoundingCaps = capabilities.BoundingCaps
creds.InheritableCaps = capabilities.InheritableCaps
// TODO: Support ambient capabilities.
} else {
// If no capabilities are specified, grant capabilities consistent with
// setresuid + setresgid from NewRootCredentials to the given uid and
// gid.
if kuid == RootKUID {
creds.PermittedCaps = AllCapabilities
creds.EffectiveCaps = AllCapabilities
} else {
creds.PermittedCaps = 0
creds.EffectiveCaps = 0
}
creds.BoundingCaps = AllCapabilities
}
return creds
}
// Fork generates an identical copy of a set of credentials.
func (c *Credentials) Fork() *Credentials {
nc := new(Credentials)
*nc = *c // Copy-by-value; this is legal for all fields.
return nc
}
// InGroup returns true if c is in group kgid. Compare Linux's
// kernel/groups.c:in_group_p().
func (c *Credentials) InGroup(kgid KGID) bool {
if c.EffectiveKGID == kgid {
return true
}
for _, extraKGID := range c.ExtraKGIDs {
if extraKGID == kgid {
return true
}
}
return false
}
// HasCapabilityIn returns true if c has capability cp in ns.
func (c *Credentials) HasCapabilityIn(cp linux.Capability, ns *UserNamespace) bool {
for {
// "1. A process has a capability inside a user namespace if it is a member
// of that namespace and it has the capability in its effective capability
// set." - user_namespaces(7)
if c.UserNamespace == ns {
return CapabilitySetOf(cp)&c.EffectiveCaps != 0
}
// "3. ... A process that resides in the parent of the user namespace and
// whose effective user ID matches the owner of the namespace has all
// capabilities in the namespace."
if c.UserNamespace == ns.parent && c.EffectiveKUID == ns.owner {
return true
}
// "2. If a process has a capability in a user namespace, then it has that
// capability in all child (and further removed descendant) namespaces as
// well."
if ns.parent == nil {
return false
}
ns = ns.parent
}
}
// HasCapability returns true if c has capability cp in its user namespace.
func (c *Credentials) HasCapability(cp linux.Capability) bool {
return c.HasCapabilityIn(cp, c.UserNamespace)
}
// UseUID checks that c can use uid in its user namespace, then translates it
// to the root user namespace.
//
// The checks UseUID does are common, but you should verify that it's doing
// exactly what you want.
func (c *Credentials) UseUID(uid UID) (KUID, error) {
// uid must be mapped.
kuid := c.UserNamespace.MapToKUID(uid)
if !kuid.Ok() {
return NoID, syserror.EINVAL
}
// If c has CAP_SETUID, then it can use any UID in its user namespace.
if c.HasCapability(linux.CAP_SETUID) {
return kuid, nil
}
// Otherwise, c must already have the UID as its real, effective, or saved
// set-user-ID.
if kuid == c.RealKUID || kuid == c.EffectiveKUID || kuid == c.SavedKUID {
return kuid, nil
}
return NoID, syserror.EPERM
}
// UseGID checks that c can use gid in its user namespace, then translates it
// to the root user namespace.
func (c *Credentials) UseGID(gid GID) (KGID, error) {
kgid := c.UserNamespace.MapToKGID(gid)
if !kgid.Ok() {
return NoID, syserror.EINVAL
}
if c.HasCapability(linux.CAP_SETGID) {
return kgid, nil
}
if kgid == c.RealKGID || kgid == c.EffectiveKGID || kgid == c.SavedKGID {
return kgid, nil
}
return NoID, syserror.EPERM
}
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