| // Copyright 2021 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. |
| |
| package syscall |
| |
| import ( |
| "runtime" |
| "unsafe" |
| ) |
| |
| type SysProcAttr struct { |
| Chroot string // Chroot. |
| Credential *Credential // Credential. |
| Ptrace bool // Enable tracing. |
| 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) |
| Jail int // Jail to which the child process is attached (FreeBSD only). |
| } |
| |
| const ( |
| _P_PID = 0 |
| |
| _PROC_PDEATHSIG_CTL = 11 |
| ) |
| |
| // Implemented in runtime package. |
| func runtime_BeforeFork() |
| func runtime_AfterFork() |
| func runtime_AfterForkInChild() |
| |
| // 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) { |
| // Declare all variables at top in case any |
| // declarations require heap allocation (e.g., err1). |
| var ( |
| r1 uintptr |
| err1 Errno |
| nextfd int |
| i int |
| pgrp _C_int |
| cred *Credential |
| ngroups, groups uintptr |
| upid uintptr |
| ) |
| |
| rlim := origRlimitNofile.Load() |
| |
| // Record parent PID so child can test if it has died. |
| ppid, _, _ := RawSyscall(SYS_GETPID, 0, 0, 0) |
| |
| // 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++ |
| |
| // About to call fork. |
| // No more allocation or calls of non-assembly functions. |
| runtime_BeforeFork() |
| r1, _, err1 = RawSyscall(SYS_FORK, 0, 0, 0) |
| if err1 != 0 { |
| runtime_AfterFork() |
| return 0, err1 |
| } |
| |
| if r1 != 0 { |
| // parent; return PID |
| runtime_AfterFork() |
| return int(r1), 0 |
| } |
| |
| // Fork succeeded, now in child. |
| |
| // Attach to the given jail, if any. The system call also changes the |
| // process' root and working directories to the jail's path directory. |
| if sys.Jail > 0 { |
| _, _, err1 = RawSyscall(SYS_JAIL_ATTACH, uintptr(sys.Jail), 0, 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 || sys.Foreground { |
| // Place child in process group. |
| _, _, err1 = RawSyscall(SYS_SETPGID, 0, uintptr(sys.Pgid), 0) |
| if err1 != 0 { |
| goto childerror |
| } |
| } |
| |
| if sys.Foreground { |
| // This should really be pid_t, however _C_int (aka int32) is |
| // generally equivalent. |
| pgrp = _C_int(sys.Pgid) |
| if pgrp == 0 { |
| r1, _, err1 = RawSyscall(SYS_GETPID, 0, 0, 0) |
| if err1 != 0 { |
| goto childerror |
| } |
| |
| pgrp = _C_int(r1) |
| } |
| |
| // Place process group in foreground. |
| _, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSPGRP), uintptr(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() |
| |
| // 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)) |
| groups = uintptr(0) |
| if ngroups > 0 { |
| groups = uintptr(unsafe.Pointer(&cred.Groups[0])) |
| } |
| if !cred.NoSetGroups { |
| _, _, err1 = RawSyscall(SYS_SETGROUPS, ngroups, 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 |
| } |
| } |
| |
| // Parent death signal |
| if sys.Pdeathsig != 0 { |
| switch runtime.GOARCH { |
| case "386", "arm": |
| _, _, err1 = RawSyscall6(SYS_PROCCTL, _P_PID, 0, 0, _PROC_PDEATHSIG_CTL, uintptr(unsafe.Pointer(&sys.Pdeathsig)), 0) |
| default: |
| _, _, err1 = RawSyscall6(SYS_PROCCTL, _P_PID, 0, _PROC_PDEATHSIG_CTL, uintptr(unsafe.Pointer(&sys.Pdeathsig)), 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 != ppid { |
| upid, _, _ = RawSyscall(SYS_GETPID, 0, 0, 0) |
| _, _, err1 = RawSyscall(SYS_KILL, upid, uintptr(sys.Pdeathsig), 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_FCNTL, uintptr(pipe), F_DUP2FD_CLOEXEC, uintptr(nextfd)) |
| if err1 != 0 { |
| goto childerror |
| } |
| pipe = nextfd |
| nextfd++ |
| } |
| for i = 0; i < len(fd); i++ { |
| if fd[i] >= 0 && fd[i] < i { |
| if nextfd == pipe { // don't stomp on pipe |
| nextfd++ |
| } |
| _, _, err1 = RawSyscall(SYS_FCNTL, uintptr(fd[i]), F_DUP2FD_CLOEXEC, uintptr(nextfd)) |
| 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 { |
| RawSyscall(SYS_CLOSE, uintptr(i), 0, 0) |
| continue |
| } |
| if fd[i] == 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 { |
| _, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSCTTY), 0) |
| if err1 != 0 { |
| goto childerror |
| } |
| } |
| |
| // Restore original rlimit. |
| if rlim != nil { |
| RawSyscall(SYS_SETRLIMIT, uintptr(RLIMIT_NOFILE), uintptr(unsafe.Pointer(rlim)), 0) |
| } |
| |
| // 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) |
| } |
| } |
| |
| // forkAndExecFailureCleanup cleans up after an exec failure. |
| func forkAndExecFailureCleanup(attr *ProcAttr, sys *SysProcAttr) { |
| // Nothing to do. |
| } |