Imported Upstream version 1.4upstream/1.4

1 files changed, 363 insertions, 0 deletions

diff --git a/src/syscall/exec_linux.go b/src/syscall/exec_linux.go
new file mode 100644
index 000000000..042c20a46
--- /dev/null
+++ b/src/syscall/exec_linux.go
@@ -0,0 +1,363 @@
+// 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.
+
+// +build linux
+
+package syscall
+
+import (
+	"unsafe"
+)
+
+// 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      bool           // Enable tracing.
+	Setsid      bool           // Create session.
+	Setpgid     bool           // Set process group ID to new pid (SYSV setpgrp)
+	Setctty     bool           // Set controlling terminal to fd Ctty (only meaningful if Setsid is set)
+	Noctty      bool           // Detach fd 0 from controlling terminal
+	Ctty        int            // Controlling TTY fd (Linux only)
+	Pdeathsig   Signal         // Signal that the process will get when its parent dies (Linux only)
+	Cloneflags  uintptr        // Flags for clone calls (Linux only)
+	UidMappings []SysProcIDMap // User ID mappings for user namespaces.
+	GidMappings []SysProcIDMap // Group ID mappings for user namespaces.
+}
+
+// Implemented in runtime package.
+func runtime_BeforeFork()
+func runtime_AfterFork()
+
+// 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.
+func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (pid int, err Errno) {
+	// Declare all variables at top in case any
+	// declarations require heap allocation (e.g., err1).
+	var (
+		r1     uintptr
+		err1   Errno
+		err2   Errno
+		nextfd int
+		i      int
+		p      [2]int
+	)
+
+	// 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 {
+			return 0, err.(Errno)
+		}
+	}
+
+	// About to call fork.
+	// No more allocation or calls of non-assembly functions.
+	runtime_BeforeFork()
+	r1, _, err1 = RawSyscall6(SYS_CLONE, uintptr(SIGCHLD)|sys.Cloneflags, 0, 0, 0, 0, 0)
+	if err1 != 0 {
+		runtime_AfterFork()
+		return 0, err1
+	}
+
+	if r1 != 0 {
+		// parent; return PID
+		runtime_AfterFork()
+		pid = int(r1)
+
+		if sys.UidMappings != nil || sys.GidMappings != nil {
+			Close(p[0])
+			err := writeUidGidMappings(pid, sys)
+			if err != nil {
+				err2 = err.(Errno)
+			}
+			RawSyscall(SYS_WRITE, uintptr(p[1]), uintptr(unsafe.Pointer(&err2)), unsafe.Sizeof(err2))
+			Close(p[1])
+		}
+
+		return pid, 0
+	}
+
+	// Fork succeeded, now in child.
+
+	// Wait for User ID/Group ID mappings to be written.
+	if sys.UidMappings != nil || sys.GidMappings != nil {
+		if _, _, err1 = RawSyscall(SYS_CLOSE, uintptr(p[1]), 0, 0); err1 != 0 {
+			goto childerror
+		}
+		r1, _, err1 = RawSyscall(SYS_READ, uintptr(p[0]), uintptr(unsafe.Pointer(&err2)), unsafe.Sizeof(err2))
+		if err1 != 0 {
+			goto childerror
+		}
+		if r1 != unsafe.Sizeof(err2) {
+			err1 = EINVAL
+			goto childerror
+		}
+		if err2 != 0 {
+			err1 = err2
+			goto childerror
+		}
+	}
+
+	// Parent death signal
+	if sys.Pdeathsig != 0 {
+		_, _, err1 = RawSyscall6(SYS_PRCTL, PR_SET_PDEATHSIG, uintptr(sys.Pdeathsig), 0, 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, _, _ = RawSyscall(SYS_GETPPID, 0, 0, 0)
+		if r1 == 1 {
+			pid, _, _ := RawSyscall(SYS_GETPID, 0, 0, 0)
+			_, _, err1 := RawSyscall(SYS_KILL, pid, uintptr(sys.Pdeathsig), 0)
+			if err1 != 0 {
+				goto childerror
+			}
+		}
+	}
+
+	// Enable tracing if requested.
+	if sys.Ptrace {
+		_, _, err1 = RawSyscall(SYS_PTRACE, uintptr(PTRACE_TRACEME), 0, 0)
+		if err1 != 0 {
+			goto childerror
+		}
+	}
+
+	// Session ID
+	if sys.Setsid {
+		_, _, err1 = RawSyscall(SYS_SETSID, 0, 0, 0)
+		if err1 != 0 {
+			goto childerror
+		}
+	}
+
+	// Set process group
+	if sys.Setpgid {
+		_, _, err1 = RawSyscall(SYS_SETPGID, 0, 0, 0)
+		if err1 != 0 {
+			goto childerror
+		}
+	}
+
+	// Chroot
+	if chroot != nil {
+		_, _, err1 = RawSyscall(SYS_CHROOT, uintptr(unsafe.Pointer(chroot)), 0, 0)
+		if err1 != 0 {
+			goto childerror
+		}
+	}
+
+	// User and groups
+	if cred := sys.Credential; cred != nil {
+		ngroups := uintptr(len(cred.Groups))
+		var groups unsafe.Pointer
+		if ngroups > 0 {
+			groups = unsafe.Pointer(&cred.Groups[0])
+		}
+		_, _, err1 = RawSyscall(SYS_SETGROUPS, ngroups, uintptr(groups), 0)
+		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
+		}
+	}
+
+	// Chdir
+	if dir != nil {
+		_, _, err1 = RawSyscall(SYS_CHDIR, uintptr(unsafe.Pointer(dir)), 0, 0)
+		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 = RawSyscall(SYS_DUP2, uintptr(pipe), uintptr(nextfd), 0)
+		if err1 != 0 {
+			goto childerror
+		}
+		RawSyscall(SYS_FCNTL, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
+		pipe = nextfd
+		nextfd++
+	}
+	for i = 0; i < len(fd); i++ {
+		if fd[i] >= 0 && fd[i] < int(i) {
+			_, _, err1 = RawSyscall(SYS_DUP2, uintptr(fd[i]), uintptr(nextfd), 0)
+			if err1 != 0 {
+				goto childerror
+			}
+			RawSyscall(SYS_FCNTL, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
+			fd[i] = nextfd
+			nextfd++
+			if nextfd == pipe { // don't stomp on pipe
+				nextfd++
+			}
+		}
+	}
+
+	// Pass 2: dup fd[i] down onto i.
+	for i = 0; i < len(fd); i++ {
+		if fd[i] == -1 {
+			RawSyscall(SYS_CLOSE, uintptr(i), 0, 0)
+			continue
+		}
+		if fd[i] == int(i) {
+			// dup2(i, i) won't clear close-on-exec flag on Linux,
+			// probably not elsewhere either.
+			_, _, err1 = RawSyscall(SYS_FCNTL, uintptr(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 = RawSyscall(SYS_DUP2, uintptr(fd[i]), uintptr(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++ {
+		RawSyscall(SYS_CLOSE, uintptr(i), 0, 0)
+	}
+
+	// Detach fd 0 from tty
+	if sys.Noctty {
+		_, _, err1 = RawSyscall(SYS_IOCTL, 0, uintptr(TIOCNOTTY), 0)
+		if err1 != 0 {
+			goto childerror
+		}
+	}
+
+	// Set the controlling TTY to Ctty
+	if sys.Setctty && sys.Ctty >= 0 {
+		_, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSCTTY), 0)
+		if err1 != 0 {
+			goto childerror
+		}
+	}
+
+	// Time to exec.
+	_, _, err1 = RawSyscall(SYS_EXECVE,
+		uintptr(unsafe.Pointer(argv0)),
+		uintptr(unsafe.Pointer(&argv[0])),
+		uintptr(unsafe.Pointer(&envv[0])))
+
+childerror:
+	// send error code on pipe
+	RawSyscall(SYS_WRITE, uintptr(pipe), uintptr(unsafe.Pointer(&err1)), unsafe.Sizeof(err1))
+	for {
+		RawSyscall(SYS_EXIT, 253, 0, 0)
+	}
+}
+
+// Try to open a pipe with O_CLOEXEC set on both file descriptors.
+func forkExecPipe(p []int) (err error) {
+	err = Pipe2(p, O_CLOEXEC)
+	// pipe2 was added in 2.6.27 and our minimum requirement is 2.6.23, so it
+	// might not be implemented.
+	if err == ENOSYS {
+		if err = Pipe(p); err != nil {
+			return
+		}
+		if _, err = fcntl(p[0], F_SETFD, FD_CLOEXEC); err != nil {
+			return
+		}
+		_, err = fcntl(p[1], F_SETFD, FD_CLOEXEC)
+	}
+	return
+}
+
+// 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
+	}
+
+	data := ""
+	for _, im := range idMap {
+		data = data + itoa(im.ContainerID) + " " + itoa(im.HostID) + " " + itoa(im.Size) + "\n"
+	}
+
+	bytes, err := ByteSliceFromString(data)
+	if err != nil {
+		Close(fd)
+		return err
+	}
+
+	if _, err := Write(fd, bytes); err != nil {
+		Close(fd)
+		return err
+	}
+
+	if err := Close(fd); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// 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(pid) + "/uid_map"
+		if err := writeIDMappings(uidf, sys.UidMappings); err != nil {
+			return err
+		}
+	}
+
+	if sys.GidMappings != nil {
+		gidf := "/proc/" + itoa(pid) + "/gid_map"
+		if err := writeIDMappings(gidf, sys.GidMappings); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}