| // 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 |
| } |