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// Copyright 2021 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 ipc
import (
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/errors/linuxerr"
"gvisor.dev/gvisor/pkg/log"
"gvisor.dev/gvisor/pkg/sentry/fs"
"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
)
// Registry is similar to Object, but for registries. It represent an abstract
// SysV IPC registry with fields common to all SysV registries. Registry is not
// thread-safe, and should be protected using a mutex.
//
// +stateify savable
type Registry struct {
// UserNS owning the IPC namespace this registry belongs to. Immutable.
UserNS *auth.UserNamespace
// objects is a map of IDs to IPC mechanisms.
objects map[ID]Mechanism
// KeysToIDs maps a lookup key to an ID.
keysToIDs map[Key]ID
// lastIDUsed is used to find the next available ID for object creation.
lastIDUsed ID
}
// NewRegistry return a new, initialized ipc.Registry.
func NewRegistry(userNS *auth.UserNamespace) *Registry {
return &Registry{
UserNS: userNS,
objects: make(map[ID]Mechanism),
keysToIDs: make(map[Key]ID),
}
}
// Find uses key to search for and return a SysV mechanism. Find returns an
// error if an object is found by shouldn't be, or if the user doesn't have
// permission to use the object. If no object is found, Find checks create
// flag, and returns an error only if it's false.
func (r *Registry) Find(ctx context.Context, key Key, mode linux.FileMode, create, exclusive bool) (Mechanism, error) {
if id, ok := r.keysToIDs[key]; ok {
mech := r.objects[id]
mech.Lock()
defer mech.Unlock()
obj := mech.Object()
creds := auth.CredentialsFromContext(ctx)
if !obj.CheckPermissions(creds, fs.PermsFromMode(mode)) {
// The [calling process / user] does not have permission to access
// the set, and does not have the CAP_IPC_OWNER capability in the
// user namespace that governs its IPC namespace.
return nil, linuxerr.EACCES
}
if create && exclusive {
// IPC_CREAT and IPC_EXCL were specified, but an object already
// exists for key.
return nil, linuxerr.EEXIST
}
return mech, nil
}
if !create {
// No object exists for key and msgflg did not specify IPC_CREAT.
return nil, linuxerr.ENOENT
}
return nil, nil
}
// Register adds the given object into Registry.Objects, and assigns it a new
// ID. It returns an error if all IDs are exhausted.
func (r *Registry) Register(m Mechanism) error {
id, err := r.newID()
if err != nil {
return err
}
obj := m.Object()
obj.ID = id
r.objects[id] = m
r.keysToIDs[obj.Key] = id
return nil
}
// newID finds the first unused ID in the registry, and returns an error if
// non is found.
func (r *Registry) newID() (ID, error) {
// Find the next available ID.
for id := r.lastIDUsed + 1; id != r.lastIDUsed; id++ {
// Handle wrap around.
if id < 0 {
id = 0
continue
}
if r.objects[id] == nil {
r.lastIDUsed = id
return id, nil
}
}
log.Warningf("ids exhausted, they may be leaking")
// The man pages for shmget(2) mention that ENOSPC should be used if "All
// possible shared memory IDs have been taken (SHMMNI)". Other SysV
// mechanisms don't have a specific errno for running out of IDs, but they
// return ENOSPC if the max number of objects is exceeded, so we assume that
// it's the same case.
return 0, linuxerr.ENOSPC
}
// Remove removes the mechanism with the given id from the registry, and calls
// mechanism.Destroy to perform mechanism-specific removal.
func (r *Registry) Remove(id ID, creds *auth.Credentials) error {
mech := r.objects[id]
if mech == nil {
return linuxerr.EINVAL
}
mech.Lock()
defer mech.Unlock()
obj := mech.Object()
// The effective user ID of the calling process must match the creator or
// owner of the [mechanism], or the caller must be privileged.
if !obj.CheckOwnership(creds) {
return linuxerr.EPERM
}
delete(r.objects, obj.ID)
delete(r.keysToIDs, obj.Key)
mech.Destroy()
return nil
}
// ForAllObjects executes a given function for all given objects.
func (r *Registry) ForAllObjects(f func(o Mechanism)) {
for _, o := range r.objects {
f(o)
}
}
// FindByID returns the mechanism with the given ID, nil if non exists.
func (r *Registry) FindByID(id ID) Mechanism {
return r.objects[id]
}
// DissociateKey removes the association between a mechanism and its key
// (deletes it from r.keysToIDs), preventing it from being discovered by any new
// process, but not necessarily destroying it. If the given key doesn't exist,
// nothing is changed.
func (r *Registry) DissociateKey(key Key) {
delete(r.keysToIDs, key)
}
// DissociateID removes the association between a mechanism and its ID (deletes
// it from r.objects). An ID can't be removed unless the associated key is
// removed already, this is done to prevent the users from acquiring nil a
// Mechanism.
//
// Precondition: must be preceded by a call to r.DissociateKey.
func (r *Registry) DissociateID(id ID) {
delete(r.objects, id)
}
// ObjectCount returns the number of registered objects.
func (r *Registry) ObjectCount() int {
return len(r.objects)
}
// LastIDUsed returns the last used ID.
func (r *Registry) LastIDUsed() ID {
return r.lastIDUsed
}
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