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capability_set.go
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/
capability_set.go
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// Copyright 2018 The gVisor Authors.
//
// 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 (
"encoding/binary"
"fmt"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/bits"
"gvisor.dev/gvisor/pkg/errors/linuxerr"
)
// A CapabilitySet is a set of capabilities implemented as a bitset. The zero
// value of CapabilitySet is a set containing no capabilities.
type CapabilitySet uint64
// VfsCapData is equivalent to Linux's cpu_vfs_cap_data, defined
// in Linux's include/linux/capability.h.
type VfsCapData struct {
MagicEtc uint32
RootID uint32
Permitted CapabilitySet
Inheritable CapabilitySet
}
// AllCapabilities is a CapabilitySet containing all valid capabilities.
var AllCapabilities = CapabilitySetOf(linux.CAP_LAST_CAP+1) - 1
// CapabilitySetOf returns a CapabilitySet containing only the given
// capability.
func CapabilitySetOf(cp linux.Capability) CapabilitySet {
return CapabilitySet(bits.MaskOf64(int(cp)))
}
// CapabilitySetOfMany returns a CapabilitySet containing the given capabilities.
func CapabilitySetOfMany(cps []linux.Capability) CapabilitySet {
var cs uint64
for _, cp := range cps {
cs |= bits.MaskOf64(int(cp))
}
return CapabilitySet(cs)
}
// VfsCapDataOf returns a VfsCapData containing the file capabilities for the given slice of bytes.
// For each field of the cap data, which are in the structure of either vfs_cap_data or vfs_ns_cap_data,
// the bytes are ordered in little endian.
func VfsCapDataOf(data []byte) (VfsCapData, error) {
var capData VfsCapData
size := len(data)
if size < linux.XATTR_CAPS_SZ_1 {
return capData, fmt.Errorf("the size of security.capability is too small, actual size: %v", size)
}
capData.MagicEtc = binary.LittleEndian.Uint32(data[:4])
capData.Permitted = CapabilitySet(binary.LittleEndian.Uint32(data[4:8]))
capData.Inheritable = CapabilitySet(binary.LittleEndian.Uint32(data[8:12]))
// The version of the file capabilities takes first 4 bytes of the given
// slice.
version := capData.MagicEtc & linux.VFS_CAP_REVISION_MASK
switch {
case version == linux.VFS_CAP_REVISION_3 && size >= linux.XATTR_CAPS_SZ_3:
// Like version 2 file capabilities, version 3 capability
// masks are 64 bits in size. In addition, version 3 has
// the root user ID of namespace, which is encoded in the
// security.capability extended attribute.
capData.RootID = binary.LittleEndian.Uint32(data[20:24])
fallthrough
case version == linux.VFS_CAP_REVISION_2 && size >= linux.XATTR_CAPS_SZ_2:
capData.Permitted += CapabilitySet(binary.LittleEndian.Uint32(data[12:16])) << 32
capData.Inheritable += CapabilitySet(binary.LittleEndian.Uint32(data[16:20])) << 32
default:
return VfsCapData{}, fmt.Errorf("VFS_CAP_REVISION_%v with cap data size %v is not supported", version, size)
}
return capData, nil
}
// CapsFromVfsCaps returns a copy of the given creds with new capability sets
// by applying the file capability that is specified by capData.
func CapsFromVfsCaps(capData VfsCapData, creds *Credentials) (*Credentials, error) {
// If the real or effective user ID of the process is root,
// the file inheritable and permitted sets are ignored from
// `Capabilities and execution of programs by root` at capabilities(7).
if root := creds.UserNamespace.MapToKUID(RootUID); creds.EffectiveKUID == root || creds.RealKUID == root {
return creds, nil
}
effective := (capData.MagicEtc & linux.VFS_CAP_FLAGS_EFFECTIVE) > 0
permittedCaps := (capData.Permitted & creds.BoundingCaps) |
(capData.Inheritable & creds.InheritableCaps)
// P'(effective) = effective ? P'(permitted) : P'(ambient).
// The ambient capabilities has not supported yet in gVisor,
// set effective capabilities to 0 when effective bit is false.
effectiveCaps := CapabilitySet(0)
if effective {
effectiveCaps = permittedCaps
}
// Insufficient to execute correctly.
if (capData.Permitted & ^permittedCaps) != 0 {
return nil, linuxerr.EPERM
}
// If the capabilities don't change, it will return the creds'
// original copy.
if creds.PermittedCaps == permittedCaps && creds.EffectiveCaps == effectiveCaps {
return creds, nil
}
// The credentials object is immutable.
newCreds := creds.Fork()
newCreds.PermittedCaps = permittedCaps
newCreds.EffectiveCaps = effectiveCaps
return newCreds, nil
}
// TaskCapabilities represents all the capability sets for a task. Each of these
// sets is explained in greater detail in capabilities(7).
type TaskCapabilities struct {
// Permitted is a limiting superset for the effective capabilities that
// the thread may assume.
PermittedCaps CapabilitySet
// Inheritable is a set of capabilities preserved across an execve(2).
InheritableCaps CapabilitySet
// Effective is the set of capabilities used by the kernel to perform
// permission checks for the thread.
EffectiveCaps CapabilitySet
// Bounding is a limiting superset for the capabilities that a thread
// can add to its inheritable set using capset(2).
BoundingCaps CapabilitySet
// Ambient is a set of capabilities that are preserved across an
// execve(2) of a program that is not privileged.
AmbientCaps CapabilitySet
}