libgo/go/syscall/exec_bsd.go

   1 // Copyright 2011 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // +build aix darwin dragonfly freebsd netbsd openbsd solaris
   6
   7 package syscall
   8
   9 import (
  10         "unsafe"
  11 )
  12
  13 type SysProcAttr struct {
  14         Chroot     string      // Chroot.
  15         Credential *Credential // Credential.
  16         Ptrace     bool        // Enable tracing.
  17         Setsid     bool        // Create session.
  18         Setpgid    bool        // Set process group ID to Pgid, or, if Pgid == 0, to new pid.
  19         Setctty    bool        // Set controlling terminal to fd Ctty
  20         Noctty     bool        // Detach fd 0 from controlling terminal
  21         Ctty       int         // Controlling TTY fd
  22         Foreground bool        // Place child's process group in foreground. (Implies Setpgid. Uses Ctty as fd of controlling TTY)
  23         Pgid       int         // Child's process group ID if Setpgid.
  24 }
  25
  26 // Implemented in runtime package.
  27 func runtime_BeforeFork()
  28 func runtime_AfterFork()
  29
  30 // Fork, dup fd onto 0..len(fd), and exec(argv0, argvv, envv) in child.
  31 // If a dup or exec fails, write the errno error to pipe.
  32 // (Pipe is close-on-exec so if exec succeeds, it will be closed.)
  33 // In the child, this function must not acquire any locks, because
  34 // they might have been locked at the time of the fork. This means
  35 // no rescheduling, no malloc calls, and no new stack segments.
  36 // For the same reason compiler does not race instrument it.
  37 // The calls to RawSyscall are okay because they are assembly
  38 // functions that do not grow the stack.
  39 //go:norace
  40 func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (pid int, err Errno) {
  41         // Declare all variables at top in case any
  42         // declarations require heap allocation (e.g., err1).
  43         var (
  44                 r1     Pid_t
  45                 err1   Errno
  46                 nextfd int
  47                 i      int
  48         )
  49
  50         // guard against side effects of shuffling fds below.
  51         // Make sure that nextfd is beyond any currently open files so
  52         // that we can't run the risk of overwriting any of them.
  53         fd := make([]int, len(attr.Files))
  54         nextfd = len(attr.Files)
  55         for i, ufd := range attr.Files {
  56                 if nextfd < int(ufd) {
  57                         nextfd = int(ufd)
  58                 }
  59                 fd[i] = int(ufd)
  60         }
  61         nextfd++
  62
  63         // About to call fork.
  64         // No more allocation or calls of non-assembly functions.
  65         runtime_BeforeFork()
  66         r1, err1 = raw_fork()
  67         if err1 != 0 {
  68                 runtime_AfterFork()
  69                 return 0, err1
  70         }
  71
  72         if r1 != 0 {
  73                 // parent; return PID
  74                 runtime_AfterFork()
  75                 return int(r1), 0
  76         }
  77
  78         // Fork succeeded, now in child.
  79
  80         // Enable tracing if requested.
  81         if sys.Ptrace {
  82                 err1 = raw_ptrace(_PTRACE_TRACEME, 0, nil, nil)
  83                 if err1 != 0 {
  84                         goto childerror
  85                 }
  86         }
  87
  88         // Session ID
  89         if sys.Setsid {
  90                 err1 = raw_setsid()
  91                 if err1 != 0 {
  92                         goto childerror
  93                 }
  94         }
  95
  96         // Set process group
  97         if sys.Setpgid || sys.Foreground {
  98                 // Place child in process group.
  99                 err1 = raw_setpgid(0, sys.Pgid)
 100                 if err1 != 0 {
 101                         goto childerror
 102                 }
 103         }
 104
 105         if sys.Foreground {
 106                 pgrp := Pid_t(sys.Pgid)
 107                 if pgrp == 0 {
 108                         pgrp = raw_getpid()
 109                 }
 110
 111                 // Place process group in foreground.
 112                 _, err1 = raw_ioctl_ptr(sys.Ctty, TIOCSPGRP, unsafe.Pointer(&pgrp))
 113                 if err1 != 0 {
 114                         goto childerror
 115                 }
 116         }
 117
 118         // Chroot
 119         if chroot != nil {
 120                 err1 = raw_chroot(chroot)
 121                 if err1 != 0 {
 122                         goto childerror
 123                 }
 124         }
 125
 126         // User and groups
 127         if cred := sys.Credential; cred != nil {
 128                 ngroups := len(cred.Groups)
 129                 if ngroups == 0 {
 130                         err2 := setgroups(0, nil)
 131                         if err2 == nil {
 132                                 err1 = 0
 133                         } else {
 134                                 err1 = err2.(Errno)
 135                         }
 136                 } else {
 137                         groups := make([]Gid_t, ngroups)
 138                         for i, v := range cred.Groups {
 139                                 groups[i] = Gid_t(v)
 140                         }
 141                         err2 := setgroups(ngroups, &groups[0])
 142                         if err2 == nil {
 143                                 err1 = 0
 144                         } else {
 145                                 err1 = err2.(Errno)
 146                         }
 147                 }
 148                 if err1 != 0 {
 149                         goto childerror
 150                 }
 151                 err2 := Setgid(int(cred.Gid))
 152                 if err2 != nil {
 153                         err1 = err2.(Errno)
 154                         goto childerror
 155                 }
 156                 err2 = Setuid(int(cred.Uid))
 157                 if err2 != nil {
 158                         err1 = err2.(Errno)
 159                         goto childerror
 160                 }
 161         }
 162
 163         // Chdir
 164         if dir != nil {
 165                 err1 = raw_chdir(dir)
 166                 if err1 != 0 {
 167                         goto childerror
 168                 }
 169         }
 170
 171         // Pass 1: look for fd[i] < i and move those up above len(fd)
 172         // so that pass 2 won't stomp on an fd it needs later.
 173         if pipe < nextfd {
 174                 err1 = raw_dup2(pipe, nextfd)
 175                 if err1 != 0 {
 176                         goto childerror
 177                 }
 178                 raw_fcntl(nextfd, F_SETFD, FD_CLOEXEC)
 179                 pipe = nextfd
 180                 nextfd++
 181         }
 182         for i = 0; i < len(fd); i++ {
 183                 if fd[i] >= 0 && fd[i] < int(i) {
 184                         if nextfd == pipe { // don't stomp on pipe
 185                                 nextfd++
 186                         }
 187                         err1 = raw_dup2(fd[i], nextfd)
 188                         if err1 != 0 {
 189                                 goto childerror
 190                         }
 191                         raw_fcntl(nextfd, F_SETFD, FD_CLOEXEC)
 192                         fd[i] = nextfd
 193                         nextfd++
 194                 }
 195         }
 196
 197         // Pass 2: dup fd[i] down onto i.
 198         for i = 0; i < len(fd); i++ {
 199                 if fd[i] == -1 {
 200                         raw_close(i)
 201                         continue
 202                 }
 203                 if fd[i] == int(i) {
 204                         // dup2(i, i) won't clear close-on-exec flag on Linux,
 205                         // probably not elsewhere either.
 206                         _, err1 = raw_fcntl(fd[i], F_SETFD, 0)
 207                         if err1 != 0 {
 208                                 goto childerror
 209                         }
 210                         continue
 211                 }
 212                 // The new fd is created NOT close-on-exec,
 213                 // which is exactly what we want.
 214                 err1 = raw_dup2(fd[i], i)
 215                 if err1 != 0 {
 216                         goto childerror
 217                 }
 218         }
 219
 220         // By convention, we don't close-on-exec the fds we are
 221         // started with, so if len(fd) < 3, close 0, 1, 2 as needed.
 222         // Programs that know they inherit fds >= 3 will need
 223         // to set them close-on-exec.
 224         for i = len(fd); i < 3; i++ {
 225                 raw_close(i)
 226         }
 227
 228         // Detach fd 0 from tty
 229         if sys.Noctty {
 230                 _, err1 = raw_ioctl(0, TIOCNOTTY, 0)
 231                 if err1 != 0 {
 232                         goto childerror
 233                 }
 234         }
 235
 236         // Set the controlling TTY to Ctty
 237         if sys.Setctty {
 238                 if TIOCSCTTY == 0 {
 239                         err1 = ENOSYS
 240                         goto childerror
 241                 }
 242                 _, err1 = raw_ioctl(sys.Ctty, TIOCSCTTY, 0)
 243                 if err1 != 0 {
 244                         goto childerror
 245                 }
 246         }
 247
 248         // Time to exec.
 249         err1 = raw_execve(argv0, &argv[0], &envv[0])
 250
 251 childerror:
 252         // send error code on pipe
 253         raw_write(pipe, (*byte)(unsafe.Pointer(&err1)), int(unsafe.Sizeof(err1)))
 254         for {
 255                 raw_exit(253)
 256         }
 257 }
 258
 259 // Try to open a pipe with O_CLOEXEC set on both file descriptors.
 260 func forkExecPipe(p []int) error {
 261         err := Pipe(p)
 262         if err != nil {
 263                 return err
 264         }
 265         _, err = fcntl(p[0], F_SETFD, FD_CLOEXEC)
 266         if err != nil {
 267                 return err
 268         }
 269         _, err = fcntl(p[1], F_SETFD, FD_CLOEXEC)
 270         return err
 271 }