1 files changed, 475 insertions, 0 deletions
diff --git a/pkg/sentry/kernel/task_clone.go b/pkg/sentry/kernel/task_clone.go
new file mode 100644
index 000000000..3a74abdfb
--- /dev/null
+++ b/pkg/sentry/kernel/task_clone.go
@@ -0,0 +1,475 @@
+// Copyright 2018 Google Inc.
+//
+// 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 kernel
+
+import (
+	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
+	"gvisor.googlesource.com/gvisor/pkg/bpf"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+	"gvisor.googlesource.com/gvisor/pkg/syserror"
+)
+
+// SharingOptions controls what resources are shared by a new task created by
+// Task.Clone, or an existing task affected by Task.Unshare.
+type SharingOptions struct {
+	// If NewAddressSpace is true, the task should have an independent virtual
+	// address space.
+	NewAddressSpace bool
+
+	// If NewSignalHandlers is true, the task should use an independent set of
+	// signal handlers.
+	NewSignalHandlers bool
+
+	// If NewThreadGroup is true, the task should be the leader of its own
+	// thread group. TerminationSignal is the signal that the thread group
+	// will send to its parent when it exits. If NewThreadGroup is false,
+	// TerminationSignal is ignored.
+	NewThreadGroup    bool
+	TerminationSignal linux.Signal
+
+	// If NewPIDNamespace is true:
+	//
+	// - In the context of Task.Clone, the new task should be the init task
+	// (TID 1) in a new PID namespace.
+	//
+	// - In the context of Task.Unshare, the task should create a new PID
+	// namespace, and all subsequent clones of the task should be members of
+	// the new PID namespace.
+	NewPIDNamespace bool
+
+	// If NewUserNamespace is true, the task should have an independent user
+	// namespace.
+	NewUserNamespace bool
+
+	// If NewNetworkNamespace is true, the task should have an independent
+	// network namespace. (Note that network namespaces are not really
+	// implemented; see comment on Task.netns for details.)
+	NewNetworkNamespace bool
+
+	// If NewFiles is true, the task should use an independent file descriptor
+	// table.
+	NewFiles bool
+
+	// If NewFSContext is true, the task should have an independent FSContext.
+	NewFSContext bool
+
+	// If NewUTSNamespace is true, the task should have an independent UTS
+	// namespace.
+	NewUTSNamespace bool
+
+	// If NewIPCNamespace is true, the task should have an independent IPC
+	// namespace.
+	NewIPCNamespace bool
+}
+
+// CloneOptions controls the behavior of Task.Clone.
+type CloneOptions struct {
+	// SharingOptions defines the set of resources that the new task will share
+	// with its parent.
+	SharingOptions
+
+	// Stack is the initial stack pointer of the new task. If Stack is 0, the
+	// new task will start with the same stack pointer as its parent.
+	Stack usermem.Addr
+
+	// If SetTLS is true, set the new task's TLS (thread-local storage)
+	// descriptor to TLS. If SetTLS is false, TLS is ignored.
+	SetTLS bool
+	TLS    usermem.Addr
+
+	// If ChildClearTID is true, when the child exits, 0 is written to the
+	// address ChildTID in the child's memory, and if the write is successful a
+	// futex wake on the same address is performed.
+	//
+	// If ChildSetTID is true, the child's thread ID (in the child's PID
+	// namespace) is written to address ChildTID in the child's memory. (As in
+	// Linux, failed writes are silently ignored.)
+	ChildClearTID bool
+	ChildSetTID   bool
+	ChildTID      usermem.Addr
+
+	// If ParentSetTID is true, the child's thread ID (in the parent's PID
+	// namespace) is written to address ParentTID in the parent's memory. (As
+	// in Linux, failed writes are silently ignored.)
+	//
+	// Older versions of the clone(2) man page state that CLONE_PARENT_SETTID
+	// causes the child's thread ID to be written to ptid in both the parent
+	// and child's memory, but this is a documentation error fixed by
+	// 87ab04792ced ("clone.2: Fix description of CLONE_PARENT_SETTID").
+	ParentSetTID bool
+	ParentTID    usermem.Addr
+
+	// If Vfork is true, place the parent in vforkStop until the cloned task
+	// releases its TaskContext.
+	Vfork bool
+
+	// If Untraced is true, do not report PTRACE_EVENT_CLONE/FORK/VFORK for
+	// this clone(), and do not ptrace-attach the caller's tracer to the new
+	// task. (PTRACE_EVENT_VFORK_DONE will still be reported if appropriate).
+	Untraced bool
+
+	// If InheritTracer is true, ptrace-attach the caller's tracer to the new
+	// task, even if no PTRACE_EVENT_CLONE/FORK/VFORK event would be reported
+	// for it. If both Untraced and InheritTracer are true, no event will be
+	// reported, but tracer inheritance will still occur.
+	InheritTracer bool
+}
+
+// Clone implements the clone(2) syscall and returns the thread ID of the new
+// task in t's PID namespace. Clone may return both a non-zero thread ID and a
+// non-nil error.
+//
+// Preconditions: The caller must be running Task.doSyscallInvoke on the task
+// goroutine.
+func (t *Task) Clone(opts *CloneOptions) (ThreadID, *SyscallControl, error) {
+	// Since signal actions may refer to application signal handlers by virtual
+	// address, any set of signal handlers must refer to the same address
+	// space.
+	if !opts.NewSignalHandlers && opts.NewAddressSpace {
+		return 0, nil, syserror.EINVAL
+	}
+	// In order for the behavior of thread-group-directed signals to be sane,
+	// all tasks in a thread group must share signal handlers.
+	if !opts.NewThreadGroup && opts.NewSignalHandlers {
+		return 0, nil, syserror.EINVAL
+	}
+	// All tasks in a thread group must be in the same PID namespace.
+	if !opts.NewThreadGroup && (opts.NewPIDNamespace || t.childPIDNamespace != nil) {
+		return 0, nil, syserror.EINVAL
+	}
+	// The two different ways of specifying a new PID namespace are
+	// incompatible.
+	if opts.NewPIDNamespace && t.childPIDNamespace != nil {
+		return 0, nil, syserror.EINVAL
+	}
+	// Thread groups and FS contexts cannot span user namespaces.
+	if opts.NewUserNamespace && (!opts.NewThreadGroup || !opts.NewFSContext) {
+		return 0, nil, syserror.EINVAL
+	}
+
+	// "If CLONE_NEWUSER is specified along with other CLONE_NEW* flags in a
+	// single clone(2) or unshare(2) call, the user namespace is guaranteed to
+	// be created first, giving the child (clone(2)) or caller (unshare(2))
+	// privileges over the remaining namespaces created by the call." -
+	// user_namespaces(7)
+	creds := t.Credentials()
+	var userns *auth.UserNamespace
+	if opts.NewUserNamespace {
+		var err error
+		// "EPERM (since Linux 3.9): CLONE_NEWUSER was specified in flags and
+		// the caller is in a chroot environment (i.e., the caller's root
+		// directory does not match the root directory of the mount namespace
+		// in which it resides)." - clone(2). Neither chroot(2) nor
+		// user_namespaces(7) document this.
+		if t.IsChrooted() {
+			return 0, nil, syserror.EPERM
+		}
+		userns, err = creds.NewChildUserNamespace()
+		if err != nil {
+			return 0, nil, err
+		}
+	}
+	if (opts.NewPIDNamespace || opts.NewNetworkNamespace || opts.NewUTSNamespace) && !creds.HasCapability(linux.CAP_SYS_ADMIN) {
+		return 0, nil, syserror.EPERM
+	}
+
+	utsns := t.UTSNamespace()
+	if opts.NewUTSNamespace {
+		// Note that this must happen after NewUserNamespace so we get
+		// the new userns if there is one.
+		utsns = t.UTSNamespace().Clone(userns)
+	}
+
+	ipcns := t.IPCNamespace()
+	if opts.NewIPCNamespace {
+		// Note that "If CLONE_NEWIPC is set, then create the process in a new IPC
+		// namespace"
+		ipcns = NewIPCNamespace()
+	}
+
+	tc, err := t.tc.Fork(t, !opts.NewAddressSpace)
+	if err != nil {
+		return 0, nil, err
+	}
+	// clone() returns 0 in the child.
+	tc.Arch.SetReturn(0)
+	if opts.Stack != 0 {
+		tc.Arch.SetStack(uintptr(opts.Stack))
+	}
+	if opts.SetTLS {
+		tc.Arch.StateData().Regs.Fs_base = uint64(opts.TLS)
+	}
+
+	pidns := t.tg.pidns
+	if t.childPIDNamespace != nil {
+		pidns = t.childPIDNamespace
+	} else if opts.NewPIDNamespace {
+		pidns = pidns.NewChild(userns)
+	}
+	tg := t.tg
+	parent := t.parent
+	if opts.NewThreadGroup {
+		sh := t.tg.signalHandlers
+		if opts.NewSignalHandlers {
+			sh = sh.Fork()
+		}
+		tg = NewThreadGroup(pidns, sh, opts.TerminationSignal, tg.limits.GetCopy(), t.k.monotonicClock)
+		parent = t
+	}
+	cfg := &TaskConfig{
+		Kernel:            t.k,
+		Parent:            parent,
+		ThreadGroup:       tg,
+		TaskContext:       tc,
+		TaskResources:     t.tr.Fork(!opts.NewFiles, !opts.NewFSContext),
+		Niceness:          t.Niceness(),
+		Credentials:       creds.Fork(),
+		NetworkNamespaced: t.netns,
+		AllowedCPUMask:    t.CPUMask(),
+		UTSNamespace:      utsns,
+		IPCNamespace:      ipcns,
+	}
+	if opts.NewNetworkNamespace {
+		cfg.NetworkNamespaced = true
+	}
+	nt, err := t.tg.pidns.owner.NewTask(cfg)
+	if err != nil {
+		if opts.NewThreadGroup {
+			tg.release()
+		}
+		return 0, nil, err
+	}
+
+	// "A child process created via fork(2) inherits a copy of its parent's
+	// alternate signal stack settings" - sigaltstack(2).
+	//
+	// However kernel/fork.c:copy_process() adds a limitation to this:
+	// "sigaltstack should be cleared when sharing the same VM".
+	if opts.NewAddressSpace || opts.Vfork {
+		nt.SetSignalStack(t.SignalStack())
+	}
+
+	if userns != nil {
+		if err := nt.SetUserNamespace(userns); err != nil {
+			// This shouldn't be possible: userns was created from nt.creds, so
+			// nt should have CAP_SYS_ADMIN in userns.
+			panic("Task.Clone: SetUserNamespace failed: " + err.Error())
+		}
+	}
+
+	// This has to happen last, because e.g. ptraceClone may send a SIGSTOP to
+	// nt that it must receive before its task goroutine starts running.
+	tid := nt.k.tasks.Root.IDOfTask(nt)
+	defer nt.Start(tid)
+
+	// "If fork/clone and execve are allowed by @prog, any child processes will
+	// be constrained to the same filters and system call ABI as the parent." -
+	// Documentation/prctl/seccomp_filter.txt
+	nt.syscallFilters = append([]bpf.Program(nil), t.syscallFilters...)
+	if opts.Vfork {
+		nt.vforkParent = t
+	}
+
+	if opts.ChildClearTID {
+		nt.SetClearTID(opts.ChildTID)
+	}
+	if opts.ChildSetTID {
+		// Can't use Task.CopyOut, which assumes AddressSpaceActive.
+		usermem.CopyObjectOut(t, nt.MemoryManager(), opts.ChildTID, nt.ThreadID(), usermem.IOOpts{})
+	}
+	ntid := t.tg.pidns.IDOfTask(nt)
+	if opts.ParentSetTID {
+		t.CopyOut(opts.ParentTID, ntid)
+	}
+
+	kind := ptraceCloneKindClone
+	if opts.Vfork {
+		kind = ptraceCloneKindVfork
+	} else if opts.TerminationSignal == linux.SIGCHLD {
+		kind = ptraceCloneKindFork
+	}
+	if t.ptraceClone(kind, nt, opts) {
+		if opts.Vfork {
+			return ntid, &SyscallControl{next: &runSyscallAfterPtraceEventClone{vforkChild: nt, vforkChildTID: ntid}}, nil
+		}
+		return ntid, &SyscallControl{next: &runSyscallAfterPtraceEventClone{}}, nil
+	}
+	if opts.Vfork {
+		t.maybeBeginVforkStop(nt)
+		return ntid, &SyscallControl{next: &runSyscallAfterVforkStop{childTID: ntid}}, nil
+	}
+	return ntid, nil, nil
+}
+
+// maybeBeginVforkStop checks if a previously-started vfork child is still
+// running and has not yet released its MM, such that its parent t should enter
+// a vforkStop.
+//
+// Preconditions: The caller must be running on t's task goroutine.
+func (t *Task) maybeBeginVforkStop(child *Task) {
+	t.tg.pidns.owner.mu.RLock()
+	defer t.tg.pidns.owner.mu.RUnlock()
+	t.tg.signalHandlers.mu.Lock()
+	defer t.tg.signalHandlers.mu.Unlock()
+	if t.killedLocked() {
+		child.vforkParent = nil
+		return
+	}
+	if child.vforkParent == t {
+		t.beginInternalStopLocked((*vforkStop)(nil))
+	}
+}
+
+func (t *Task) unstopVforkParent() {
+	t.tg.pidns.owner.mu.RLock()
+	defer t.tg.pidns.owner.mu.RUnlock()
+	if p := t.vforkParent; p != nil {
+		p.tg.signalHandlers.mu.Lock()
+		defer p.tg.signalHandlers.mu.Unlock()
+		if _, ok := p.stop.(*vforkStop); ok {
+			p.endInternalStopLocked()
+		}
+		// Parent no longer needs to be unstopped.
+		t.vforkParent = nil
+	}
+}
+
+type runSyscallAfterPtraceEventClone struct {
+	vforkChild *Task
+
+	// If vforkChild is not nil, vforkChildTID is its thread ID in the parent's
+	// PID namespace. vforkChildTID must be stored since the child may exit and
+	// release its TID before the PTRACE_EVENT stop ends.
+	vforkChildTID ThreadID
+}
+
+func (r *runSyscallAfterPtraceEventClone) execute(t *Task) taskRunState {
+	if r.vforkChild != nil {
+		t.maybeBeginVforkStop(r.vforkChild)
+		return &runSyscallAfterVforkStop{r.vforkChildTID}
+	}
+	return (*runSyscallExit)(nil)
+}
+
+type runSyscallAfterVforkStop struct {
+	// childTID has the same meaning as
+	// runSyscallAfterPtraceEventClone.vforkChildTID.
+	childTID ThreadID
+}
+
+func (r *runSyscallAfterVforkStop) execute(t *Task) taskRunState {
+	t.ptraceVforkDone(r.childTID)
+	return (*runSyscallExit)(nil)
+}
+
+// Unshare changes the set of resources t shares with other tasks, as specified
+// by opts.
+//
+// Preconditions: The caller must be running on the task goroutine.
+func (t *Task) Unshare(opts *SharingOptions) error {
+	// In Linux unshare(2), NewThreadGroup implies NewSignalHandlers and
+	// NewSignalHandlers implies NewAddressSpace. All three flags are no-ops if
+	// t is the only task using its MM, which due to clone(2)'s rules imply
+	// that it is also the only task using its signal handlers / in its thread
+	// group, and cause EINVAL to be returned otherwise.
+	//
+	// Since we don't count the number of tasks using each address space or set
+	// of signal handlers, we reject NewSignalHandlers and NewAddressSpace
+	// altogether, and interpret NewThreadGroup as requiring that t be the only
+	// member of its thread group. This seems to be logically coherent, in the
+	// sense that clone(2) allows a task to share signal handlers and address
+	// spaces with tasks in other thread groups.
+	if opts.NewAddressSpace || opts.NewSignalHandlers {
+		return syserror.EINVAL
+	}
+	if opts.NewThreadGroup {
+		t.tg.signalHandlers.mu.Lock()
+		if t.tg.tasksCount != 1 {
+			t.tg.signalHandlers.mu.Unlock()
+			return syserror.EINVAL
+		}
+		t.tg.signalHandlers.mu.Unlock()
+		// This isn't racy because we're the only living task, and therefore
+		// the only task capable of creating new ones, in our thread group.
+	}
+	if opts.NewUserNamespace {
+		if t.IsChrooted() {
+			return syserror.EPERM
+		}
+		// This temporary is needed because Go.
+		creds := t.Credentials()
+		newUserNS, err := creds.NewChildUserNamespace()
+		if err != nil {
+			return err
+		}
+		err = t.SetUserNamespace(newUserNS)
+		if err != nil {
+			return err
+		}
+	}
+	haveCapSysAdmin := t.HasCapability(linux.CAP_SYS_ADMIN)
+	if opts.NewPIDNamespace {
+		if !haveCapSysAdmin {
+			return syserror.EPERM
+		}
+		t.childPIDNamespace = t.tg.pidns.NewChild(t.UserNamespace())
+	}
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	if opts.NewNetworkNamespace {
+		if !haveCapSysAdmin {
+			return syserror.EPERM
+		}
+		t.netns = true
+	}
+	if opts.NewUTSNamespace {
+		if !haveCapSysAdmin {
+			return syserror.EPERM
+		}
+		// Note that this must happen after NewUserNamespace, so the
+		// new user namespace is used if there is one.
+		t.utsns = t.utsns.Clone(t.creds.UserNamespace)
+	}
+	if opts.NewIPCNamespace {
+		if !haveCapSysAdmin {
+			return syserror.EPERM
+		}
+		// Note that "If CLONE_NEWIPC is set, then create the process in a new IPC
+		// namespace"
+		t.ipcns = NewIPCNamespace()
+	}
+	if opts.NewFiles {
+		oldFDMap := t.tr.FDMap
+		t.tr.FDMap = oldFDMap.Fork()
+		oldFDMap.DecRef()
+	}
+	if opts.NewFSContext {
+		oldFS := t.tr.FSContext
+		t.tr.FSContext = oldFS.Fork()
+		oldFS.DecRef()
+	}
+	return nil
+}
+
+// vforkStop is a TaskStop imposed on a task that creates a child with
+// CLONE_VFORK or vfork(2), that ends when the child task ceases to use its
+// current MM. (Normally, CLONE_VFORK is used in conjunction with CLONE_VM, so
+// that the child and parent share mappings until the child execve()s into a
+// new process image or exits.)
+type vforkStop struct{}
+
+// StopIgnoresKill implements TaskStop.Killable.
+func (*vforkStop) Killable() bool { return true }