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- // Copyright 2011 The Go Authors. All rights reserved.
- // Use of this source code is governed by a BSD-style
- // license that can be found in the LICENSE file.
- //go:build linux
- package syscall
- import (
- "internal/itoa"
- "unsafe"
- )
- //sysnb raw_prctl(option int, arg2 int, arg3 int, arg4 int, arg5 int) (ret int, err Errno)
- //prctl(option _C_int, arg2 _C_long, arg3 _C_long, arg4 _C_long, arg5 _C_long) _C_int
- //sysnb rawUnshare(flags int) (err Errno)
- //unshare(flags _C_int) _C_int
- //sysnb rawMount(source *byte, target *byte, fstype *byte, flags uintptr, data *byte) (err Errno)
- //mount(source *byte, target *byte, fstype *byte, flags _C_long, data *byte) _C_int
- //sysnb rawOpenat(dirfd int, pathname *byte, flags int, perm uint32) (fd int, err Errno)
- //__go_openat(dirfd _C_int, pathname *byte, flags _C_int, perm Mode_t) _C_int
- // SysProcIDMap holds Container ID to Host ID mappings used for User Namespaces in Linux.
- // See user_namespaces(7).
- type SysProcIDMap struct {
- ContainerID int // Container ID.
- HostID int // Host ID.
- Size int // Size.
- }
- type SysProcAttr struct {
- Chroot string // Chroot.
- Credential *Credential // Credential.
- // Ptrace tells the child to call ptrace(PTRACE_TRACEME).
- // Call runtime.LockOSThread before starting a process with this set,
- // and don't call UnlockOSThread until done with PtraceSyscall calls.
- Ptrace bool
- Setsid bool // Create session.
- // Setpgid sets the process group ID of the child to Pgid,
- // or, if Pgid == 0, to the new child's process ID.
- Setpgid bool
- // Setctty sets the controlling terminal of the child to
- // file descriptor Ctty. Ctty must be a descriptor number
- // in the child process: an index into ProcAttr.Files.
- // This is only meaningful if Setsid is true.
- Setctty bool
- Noctty bool // Detach fd 0 from controlling terminal
- Ctty int // Controlling TTY fd
- // Foreground places the child process group in the foreground.
- // This implies Setpgid. The Ctty field must be set to
- // the descriptor of the controlling TTY.
- // Unlike Setctty, in this case Ctty must be a descriptor
- // number in the parent process.
- Foreground bool
- Pgid int // Child's process group ID if Setpgid.
- Pdeathsig Signal // Signal that the process will get when its parent dies (Linux and FreeBSD only)
- Cloneflags uintptr // Flags for clone calls (Linux only)
- Unshareflags uintptr // Flags for unshare calls (Linux only)
- UidMappings []SysProcIDMap // User ID mappings for user namespaces.
- GidMappings []SysProcIDMap // Group ID mappings for user namespaces.
- // GidMappingsEnableSetgroups enabling setgroups syscall.
- // If false, then setgroups syscall will be disabled for the child process.
- // This parameter is no-op if GidMappings == nil. Otherwise for unprivileged
- // users this should be set to false for mappings work.
- GidMappingsEnableSetgroups bool
- AmbientCaps []uintptr // Ambient capabilities (Linux only)
- }
- var (
- none = [...]byte{'n', 'o', 'n', 'e', 0}
- slash = [...]byte{'/', 0}
- )
- // Implemented in runtime package.
- func runtime_BeforeFork()
- func runtime_AfterFork()
- func runtime_AfterForkInChild()
- // Implemented in clone_linux.c
- //go:noescape
- func rawClone(flags _C_ulong, child_stack *byte, ptid *Pid_t, ctid *Pid_t, regs unsafe.Pointer) _C_long
- // Fork, dup fd onto 0..len(fd), and exec(argv0, argvv, envv) in child.
- // If a dup or exec fails, write the errno error to pipe.
- // (Pipe is close-on-exec so if exec succeeds, it will be closed.)
- // In the child, this function must not acquire any locks, because
- // they might have been locked at the time of the fork. This means
- // no rescheduling, no malloc calls, and no new stack segments.
- // For the same reason compiler does not race instrument it.
- // The calls to RawSyscall are okay because they are assembly
- // functions that do not grow the stack.
- //go:norace
- func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (pid int, err Errno) {
- // Set up and fork. This returns immediately in the parent or
- // if there's an error.
- r1, err1, p, locked := forkAndExecInChild1(argv0, argv, envv, chroot, dir, attr, sys, pipe)
- if locked {
- runtime_AfterFork()
- }
- if err1 != 0 {
- return 0, err1
- }
- // parent; return PID
- pid = int(r1)
- if sys.UidMappings != nil || sys.GidMappings != nil {
- Close(p[0])
- var err2 Errno
- // uid/gid mappings will be written after fork and unshare(2) for user
- // namespaces.
- if sys.Unshareflags&CLONE_NEWUSER == 0 {
- if err := writeUidGidMappings(pid, sys); err != nil {
- err2 = err.(Errno)
- }
- }
- raw_write(p[1], (*byte)(unsafe.Pointer(&err2)), int(unsafe.Sizeof(err2)))
- Close(p[1])
- }
- return pid, 0
- }
- const _LINUX_CAPABILITY_VERSION_3 = 0x20080522
- type capHeader struct {
- version uint32
- pid int32
- }
- type capData struct {
- effective uint32
- permitted uint32
- inheritable uint32
- }
- type caps struct {
- hdr capHeader
- data [2]capData
- }
- // See CAP_TO_INDEX in linux/capability.h:
- func capToIndex(cap uintptr) uintptr { return cap >> 5 }
- // See CAP_TO_MASK in linux/capability.h:
- func capToMask(cap uintptr) uint32 { return 1 << uint(cap&31) }
- // forkAndExecInChild1 implements the body of forkAndExecInChild up to
- // the parent's post-fork path. This is a separate function so we can
- // separate the child's and parent's stack frames if we're using
- // vfork.
- //
- // This is go:noinline because the point is to keep the stack frames
- // of this and forkAndExecInChild separate.
- //
- //go:noinline
- //go:norace
- func forkAndExecInChild1(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (r1 uintptr, err1 Errno, p [2]int, locked bool) {
- // Defined in linux/prctl.h starting with Linux 4.3.
- const (
- PR_CAP_AMBIENT = 0x2f
- PR_CAP_AMBIENT_RAISE = 0x2
- )
- // vfork requires that the child not touch any of the parent's
- // active stack frames. Hence, the child does all post-fork
- // processing in this stack frame and never returns, while the
- // parent returns immediately from this frame and does all
- // post-fork processing in the outer frame.
- // Declare all variables at top in case any
- // declarations require heap allocation (e.g., err1).
- var (
- err2 Errno
- nextfd int
- i int
- r2 int
- caps caps
- fd1 int
- puid, psetgroups, pgid []byte
- uidmap, setgroups, gidmap []byte
- )
- if sys.UidMappings != nil {
- puid = []byte("/proc/self/uid_map\000")
- uidmap = formatIDMappings(sys.UidMappings)
- }
- if sys.GidMappings != nil {
- psetgroups = []byte("/proc/self/setgroups\000")
- pgid = []byte("/proc/self/gid_map\000")
- if sys.GidMappingsEnableSetgroups {
- setgroups = []byte("allow\000")
- } else {
- setgroups = []byte("deny\000")
- }
- gidmap = formatIDMappings(sys.GidMappings)
- }
- // Record parent PID so child can test if it has died.
- ppid := raw_getpid()
- // Guard against side effects of shuffling fds below.
- // Make sure that nextfd is beyond any currently open files so
- // that we can't run the risk of overwriting any of them.
- fd := make([]int, len(attr.Files))
- nextfd = len(attr.Files)
- for i, ufd := range attr.Files {
- if nextfd < int(ufd) {
- nextfd = int(ufd)
- }
- fd[i] = int(ufd)
- }
- nextfd++
- // Allocate another pipe for parent to child communication for
- // synchronizing writing of User ID/Group ID mappings.
- if sys.UidMappings != nil || sys.GidMappings != nil {
- if err := forkExecPipe(p[:]); err != nil {
- err1 = err.(Errno)
- return
- }
- }
- // About to call fork.
- // No more allocation or calls of non-assembly functions.
- runtime_BeforeFork()
- locked = true
- r2 = int(rawClone(_C_ulong(uintptr(SIGCHLD)|sys.Cloneflags), nil, nil, nil, unsafe.Pointer(nil)))
- if r2 < 0 {
- err1 = GetErrno()
- }
- if r2 != 0 {
- // If we're in the parent, we must return immediately
- // so we're not in the same stack frame as the child.
- // This can at most use the return PC, which the child
- // will not modify, and the results of
- // rawVforkSyscall, which must have been written after
- // the child was replaced.
- r1 = uintptr(r2)
- return
- }
- // Fork succeeded, now in child.
- // Enable the "keep capabilities" flag to set ambient capabilities later.
- if len(sys.AmbientCaps) > 0 {
- _, err1 = raw_prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0)
- if err1 != 0 {
- goto childerror
- }
- }
- // Wait for User ID/Group ID mappings to be written.
- if sys.UidMappings != nil || sys.GidMappings != nil {
- if err1 = raw_close(p[1]); err1 != 0 {
- goto childerror
- }
- r2, err1 = raw_read(p[0], (*byte)(unsafe.Pointer(&err2)), int(unsafe.Sizeof(err2)))
- if err1 != 0 {
- goto childerror
- }
- if r2 != int(unsafe.Sizeof(err2)) {
- err1 = EINVAL
- goto childerror
- }
- if err2 != 0 {
- err1 = err2
- goto childerror
- }
- }
- // Session ID
- if sys.Setsid {
- err1 = raw_setsid()
- if err1 != 0 {
- goto childerror
- }
- }
- // Set process group
- if sys.Setpgid || sys.Foreground {
- // Place child in process group.
- err1 = raw_setpgid(0, sys.Pgid)
- if err1 != 0 {
- goto childerror
- }
- }
- if sys.Foreground {
- pgrp := Pid_t(sys.Pgid)
- if pgrp == 0 {
- pgrp = raw_getpid()
- }
- // Place process group in foreground.
- _, err1 = raw_ioctl_ptr(sys.Ctty, TIOCSPGRP, unsafe.Pointer(&pgrp))
- if err1 != 0 {
- goto childerror
- }
- }
- // Restore the signal mask. We do this after TIOCSPGRP to avoid
- // having the kernel send a SIGTTOU signal to the process group.
- runtime_AfterForkInChild()
- // Unshare
- if sys.Unshareflags != 0 {
- err1 = rawUnshare(int(sys.Unshareflags))
- if err1 != 0 {
- goto childerror
- }
- if sys.Unshareflags&CLONE_NEWUSER != 0 && sys.GidMappings != nil {
- dirfd := int(_AT_FDCWD)
- if fd1, err1 = rawOpenat(dirfd, &psetgroups[0], O_WRONLY, 0); err1 != 0 {
- goto childerror
- }
- _, err1 = raw_write(fd1, &setgroups[0], len(setgroups))
- if err1 != 0 {
- goto childerror
- }
- if err1 = raw_close(fd1); err1 != 0 {
- goto childerror
- }
- if fd1, err1 = rawOpenat(dirfd, &pgid[0], O_WRONLY, 0); err1 != 0 {
- goto childerror
- }
- _, err1 = raw_write(fd1, &gidmap[0], len(gidmap))
- if err1 != 0 {
- goto childerror
- }
- if err1 = raw_close(fd1); err1 != 0 {
- goto childerror
- }
- }
- if sys.Unshareflags&CLONE_NEWUSER != 0 && sys.UidMappings != nil {
- dirfd := int(_AT_FDCWD)
- if fd1, err1 = rawOpenat(dirfd, &puid[0], O_WRONLY, 0); err1 != 0 {
- goto childerror
- }
- _, err1 = raw_write(fd1, &uidmap[0], len(uidmap))
- if err1 != 0 {
- goto childerror
- }
- if err1 = raw_close(fd1); err1 != 0 {
- goto childerror
- }
- }
- // The unshare system call in Linux doesn't unshare mount points
- // mounted with --shared. Systemd mounts / with --shared. For a
- // long discussion of the pros and cons of this see debian bug 739593.
- // The Go model of unsharing is more like Plan 9, where you ask
- // to unshare and the namespaces are unconditionally unshared.
- // To make this model work we must further mark / as MS_PRIVATE.
- // This is what the standard unshare command does.
- if sys.Unshareflags&CLONE_NEWNS == CLONE_NEWNS {
- err1 = rawMount(&none[0], &slash[0], nil, MS_REC|MS_PRIVATE, nil)
- if err1 != 0 {
- goto childerror
- }
- }
- }
- // Chroot
- if chroot != nil {
- err1 = raw_chroot(chroot)
- if err1 != 0 {
- goto childerror
- }
- }
- // User and groups
- if cred := sys.Credential; cred != nil {
- ngroups := len(cred.Groups)
- var groups unsafe.Pointer
- if ngroups > 0 {
- groups = unsafe.Pointer(&cred.Groups[0])
- }
- if !(sys.GidMappings != nil && !sys.GidMappingsEnableSetgroups && ngroups == 0) && !cred.NoSetGroups {
- err1 = raw_setgroups(ngroups, groups)
- if err1 != 0 {
- goto childerror
- }
- }
- _, _, err1 = RawSyscall(sys_SETGID, uintptr(cred.Gid), 0, 0)
- if err1 != 0 {
- goto childerror
- }
- _, _, err1 = RawSyscall(sys_SETUID, uintptr(cred.Uid), 0, 0)
- if err1 != 0 {
- goto childerror
- }
- }
- if len(sys.AmbientCaps) != 0 {
- // Ambient capabilities were added in the 4.3 kernel,
- // so it is safe to always use _LINUX_CAPABILITY_VERSION_3.
- caps.hdr.version = _LINUX_CAPABILITY_VERSION_3
- if _, _, err1 = RawSyscall(SYS_CAPGET, uintptr(unsafe.Pointer(&caps.hdr)), uintptr(unsafe.Pointer(&caps.data[0])), 0); err1 != 0 {
- goto childerror
- }
- for _, c := range sys.AmbientCaps {
- // Add the c capability to the permitted and inheritable capability mask,
- // otherwise we will not be able to add it to the ambient capability mask.
- caps.data[capToIndex(c)].permitted |= capToMask(c)
- caps.data[capToIndex(c)].inheritable |= capToMask(c)
- }
- if _, _, err1 = RawSyscall(SYS_CAPSET, uintptr(unsafe.Pointer(&caps.hdr)), uintptr(unsafe.Pointer(&caps.data[0])), 0); err1 != 0 {
- goto childerror
- }
- for _, c := range sys.AmbientCaps {
- _, _, err1 = RawSyscall6(SYS_PRCTL, PR_CAP_AMBIENT, uintptr(PR_CAP_AMBIENT_RAISE), c, 0, 0, 0)
- if err1 != 0 {
- goto childerror
- }
- }
- }
- // Chdir
- if dir != nil {
- err1 = raw_chdir(dir)
- if err1 != 0 {
- goto childerror
- }
- }
- // Parent death signal
- if sys.Pdeathsig != 0 {
- _, err1 = raw_prctl(PR_SET_PDEATHSIG, int(sys.Pdeathsig), 0, 0, 0)
- if err1 != 0 {
- goto childerror
- }
- // Signal self if parent is already dead. This might cause a
- // duplicate signal in rare cases, but it won't matter when
- // using SIGKILL.
- r1 := raw_getppid()
- if r1 != ppid {
- pid := raw_getpid()
- err1 = raw_kill(pid, sys.Pdeathsig)
- if err1 != 0 {
- goto childerror
- }
- }
- }
- // Pass 1: look for fd[i] < i and move those up above len(fd)
- // so that pass 2 won't stomp on an fd it needs later.
- if pipe < nextfd {
- err1 = raw_dup3(pipe, nextfd, O_CLOEXEC)
- if err1 != 0 {
- goto childerror
- }
- pipe = nextfd
- nextfd++
- }
- for i = 0; i < len(fd); i++ {
- if fd[i] >= 0 && fd[i] < int(i) {
- if nextfd == pipe { // don't stomp on pipe
- nextfd++
- }
- err1 = raw_dup3(fd[i], nextfd, O_CLOEXEC)
- if err1 != 0 {
- goto childerror
- }
- fd[i] = nextfd
- nextfd++
- }
- }
- // Pass 2: dup fd[i] down onto i.
- for i = 0; i < len(fd); i++ {
- if fd[i] == -1 {
- raw_close(i)
- continue
- }
- if fd[i] == int(i) {
- // dup2(i, i) won't clear close-on-exec flag on Linux,
- // probably not elsewhere either.
- _, err1 = raw_fcntl(fd[i], F_SETFD, 0)
- if err1 != 0 {
- goto childerror
- }
- continue
- }
- // The new fd is created NOT close-on-exec,
- // which is exactly what we want.
- err1 = raw_dup3(fd[i], i, 0)
- if err1 != 0 {
- goto childerror
- }
- }
- // By convention, we don't close-on-exec the fds we are
- // started with, so if len(fd) < 3, close 0, 1, 2 as needed.
- // Programs that know they inherit fds >= 3 will need
- // to set them close-on-exec.
- for i = len(fd); i < 3; i++ {
- raw_close(i)
- }
- // Detach fd 0 from tty
- if sys.Noctty {
- _, err1 = raw_ioctl(0, TIOCNOTTY, 0)
- if err1 != 0 {
- goto childerror
- }
- }
- // Set the controlling TTY to Ctty
- if sys.Setctty {
- _, err1 = raw_ioctl(sys.Ctty, TIOCSCTTY, 1)
- if err1 != 0 {
- goto childerror
- }
- }
- // Enable tracing if requested.
- // Do this right before exec so that we don't unnecessarily trace the runtime
- // setting up after the fork. See issue #21428.
- if sys.Ptrace {
- err1 = raw_ptrace(_PTRACE_TRACEME, 0, 0, 0)
- if err1 != 0 {
- goto childerror
- }
- }
- // Time to exec.
- err1 = raw_execve(argv0, &argv[0], &envv[0])
- childerror:
- // send error code on pipe
- raw_write(pipe, (*byte)(unsafe.Pointer(&err1)), int(unsafe.Sizeof(err1)))
- for {
- raw_exit(253)
- }
- }
- // Try to open a pipe with O_CLOEXEC set on both file descriptors.
- func forkExecPipe(p []int) (err error) {
- return Pipe2(p, O_CLOEXEC)
- }
- func formatIDMappings(idMap []SysProcIDMap) []byte {
- var data []byte
- for _, im := range idMap {
- data = append(data, []byte(itoa.Itoa(im.ContainerID)+" "+itoa.Itoa(im.HostID)+" "+itoa.Itoa(im.Size)+"\n")...)
- }
- return data
- }
- // writeIDMappings writes the user namespace User ID or Group ID mappings to the specified path.
- func writeIDMappings(path string, idMap []SysProcIDMap) error {
- fd, err := Open(path, O_RDWR, 0)
- if err != nil {
- return err
- }
- if _, err := Write(fd, formatIDMappings(idMap)); err != nil {
- Close(fd)
- return err
- }
- if err := Close(fd); err != nil {
- return err
- }
- return nil
- }
- // writeSetgroups writes to /proc/PID/setgroups "deny" if enable is false
- // and "allow" if enable is true.
- // This is needed since kernel 3.19, because you can't write gid_map without
- // disabling setgroups() system call.
- func writeSetgroups(pid int, enable bool) error {
- sgf := "/proc/" + itoa.Itoa(pid) + "/setgroups"
- fd, err := Open(sgf, O_RDWR, 0)
- if err != nil {
- return err
- }
- var data []byte
- if enable {
- data = []byte("allow")
- } else {
- data = []byte("deny")
- }
- if _, err := Write(fd, data); err != nil {
- Close(fd)
- return err
- }
- return Close(fd)
- }
- // writeUidGidMappings writes User ID and Group ID mappings for user namespaces
- // for a process and it is called from the parent process.
- func writeUidGidMappings(pid int, sys *SysProcAttr) error {
- if sys.UidMappings != nil {
- uidf := "/proc/" + itoa.Itoa(pid) + "/uid_map"
- if err := writeIDMappings(uidf, sys.UidMappings); err != nil {
- return err
- }
- }
- if sys.GidMappings != nil {
- // If the kernel is too old to support /proc/PID/setgroups, writeSetGroups will return ENOENT; this is OK.
- if err := writeSetgroups(pid, sys.GidMappingsEnableSetgroups); err != nil && err != ENOENT {
- return err
- }
- gidf := "/proc/" + itoa.Itoa(pid) + "/gid_map"
- if err := writeIDMappings(gidf, sys.GidMappings); err != nil {
- return err
- }
- }
- return nil
- }
|