libgo/go/syscall/exec_linux.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 linux
   6
   7 package syscall
   8
   9 import (
  10         "unsafe"
  11 )
  12
  13 //sysnb raw_prctl(option int, arg2 int, arg3 int, arg4 int, arg5 int) (ret int, err Errno)
  14 //prctl(option _C_int, arg2 _C_long, arg3 _C_long, arg4 _C_long, arg5 _C_long) _C_int
  15
  16 type SysProcAttr struct {
  17         Chroot     string      // Chroot.
  18         Credential *Credential // Credential.
  19         Ptrace     bool        // Enable tracing.
  20         Setsid     bool        // Create session.
  21         Setpgid    bool        // Set process group ID to new pid (SYSV setpgrp)
  22         Setctty    bool        // Set controlling terminal to fd Ctty (only meaningful if Setsid is set)
  23         Noctty     bool        // Detach fd 0 from controlling terminal
  24         Ctty       int         // Controlling TTY fd (Linux only)
  25         Pdeathsig  Signal      // Signal that the process will get when its parent dies (Linux only)
  26         Cloneflags uintptr     // Flags for clone calls (Linux only)
  27 }
  28
  29 // Implemented in runtime package.
  30 func runtime_BeforeFork()
  31 func runtime_AfterFork()
  32
  33 // Fork, dup fd onto 0..len(fd), and exec(argv0, argvv, envv) in child.
  34 // If a dup or exec fails, write the errno error to pipe.
  35 // (Pipe is close-on-exec so if exec succeeds, it will be closed.)
  36 // In the child, this function must not acquire any locks, because
  37 // they might have been locked at the time of the fork.  This means
  38 // no rescheduling, no malloc calls, and no new stack segments.
  39 // For the same reason compiler does not race instrument it.
  40 // The calls to RawSyscall are okay because they are assembly
  41 // functions that do not grow the stack.
  42 func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (pid int, err Errno) {
  43         // Declare all variables at top in case any
  44         // declarations require heap allocation (e.g., err1).
  45         var (
  46                 r1     Pid_t
  47                 err1   Errno
  48                 nextfd int
  49                 i      int
  50         )
  51
  52         // Guard against side effects of shuffling fds below.
  53         // Make sure that nextfd is beyond any currently open files so
  54         // that we can't run the risk of overwriting any of them.
  55         fd := make([]int, len(attr.Files))
  56         nextfd = len(attr.Files)
  57         for i, ufd := range attr.Files {
  58                 if nextfd < int(ufd) {
  59                         nextfd = int(ufd)
  60                 }
  61                 fd[i] = int(ufd)
  62         }
  63         nextfd++
  64
  65         // About to call fork.
  66         // No more allocation or calls of non-assembly functions.
  67         runtime_BeforeFork()
  68         r1, err1 = raw_fork()
  69         if err1 != 0 {
  70                 runtime_AfterFork()
  71                 return 0, err1
  72         }
  73
  74         if r1 != 0 {
  75                 // parent; return PID
  76                 runtime_AfterFork()
  77                 return int(r1), 0
  78         }
  79
  80         // Fork succeeded, now in child.
  81
  82         // Parent death signal
  83         if sys.Pdeathsig != 0 {
  84                 _, err1 = raw_prctl(PR_SET_PDEATHSIG, int(sys.Pdeathsig), 0, 0, 0)
  85                 if err1 != 0 {
  86                         goto childerror
  87                 }
  88
  89                 // Signal self if parent is already dead. This might cause a
  90                 // duplicate signal in rare cases, but it won't matter when
  91                 // using SIGKILL.
  92                 ppid := Getppid()
  93                 if ppid == 1 {
  94                         pid = Getpid()
  95                         err2 := Kill(pid, sys.Pdeathsig)
  96                         if err2 != nil {
  97                                 err1 = err2.(Errno)
  98                                 goto childerror
  99                         }
 100                 }
 101         }
 102
 103         // Enable tracing if requested.
 104         if sys.Ptrace {
 105                 err1 = raw_ptrace(_PTRACE_TRACEME, 0, nil, nil)
 106                 if err1 != 0 {
 107                         goto childerror
 108                 }
 109         }
 110
 111         // Session ID
 112         if sys.Setsid {
 113                 err1 = raw_setsid()
 114                 if err1 != 0 {
 115                         goto childerror
 116                 }
 117         }
 118
 119         // Set process group
 120         if sys.Setpgid {
 121                 err1 = raw_setpgid(0, 0)
 122                 if err1 != 0 {
 123                         goto childerror
 124                 }
 125         }
 126
 127         // Chroot
 128         if chroot != nil {
 129                 err1 = raw_chroot(chroot)
 130                 if err1 != 0 {
 131                         goto childerror
 132                 }
 133         }
 134
 135         // User and groups
 136         if cred := sys.Credential; cred != nil {
 137                 ngroups := len(cred.Groups)
 138                 if ngroups == 0 {
 139                         err2 := setgroups(0, nil)
 140                         if err2 == nil {
 141                                 err1 = 0
 142                         } else {
 143                                 err1 = err2.(Errno)
 144                         }
 145                 } else {
 146                         groups := make([]Gid_t, ngroups)
 147                         for i, v := range cred.Groups {
 148                                 groups[i] = Gid_t(v)
 149                         }
 150                         err2 := setgroups(ngroups, &groups[0])
 151                         if err2 == nil {
 152                                 err1 = 0
 153                         } else {
 154                                 err1 = err2.(Errno)
 155                         }
 156                 }
 157                 if err1 != 0 {
 158                         goto childerror
 159                 }
 160                 err2 := Setgid(int(cred.Gid))
 161                 if err2 != nil {
 162                         err1 = err2.(Errno)
 163                         goto childerror
 164                 }
 165                 err2 = Setuid(int(cred.Uid))
 166                 if err2 != nil {
 167                         err1 = err2.(Errno)
 168                         goto childerror
 169                 }
 170         }
 171
 172         // Chdir
 173         if dir != nil {
 174                 err1 = raw_chdir(dir)
 175                 if err1 != 0 {
 176                         goto childerror
 177                 }
 178         }
 179
 180         // Pass 1: look for fd[i] < i and move those up above len(fd)
 181         // so that pass 2 won't stomp on an fd it needs later.
 182         if pipe < nextfd {
 183                 err1 = raw_dup2(pipe, nextfd)
 184                 if err1 != 0 {
 185                         goto childerror
 186                 }
 187                 raw_fcntl(nextfd, F_SETFD, FD_CLOEXEC)
 188                 pipe = nextfd
 189                 nextfd++
 190         }
 191         for i = 0; i < len(fd); i++ {
 192                 if fd[i] >= 0 && fd[i] < int(i) {
 193                         err1 = raw_dup2(fd[i], nextfd)
 194                         if err1 != 0 {
 195                                 goto childerror
 196                         }
 197                         raw_fcntl(nextfd, F_SETFD, FD_CLOEXEC)
 198                         fd[i] = nextfd
 199                         nextfd++
 200                         if nextfd == pipe { // don't stomp on pipe
 201                                 nextfd++
 202                         }
 203                 }
 204         }
 205
 206         // Pass 2: dup fd[i] down onto i.
 207         for i = 0; i < len(fd); i++ {
 208                 if fd[i] == -1 {
 209                         raw_close(i)
 210                         continue
 211                 }
 212                 if fd[i] == int(i) {
 213                         // dup2(i, i) won't clear close-on-exec flag on Linux,
 214                         // probably not elsewhere either.
 215                         _, err1 = raw_fcntl(fd[i], F_SETFD, 0)
 216                         if err1 != 0 {
 217                                 goto childerror
 218                         }
 219                         continue
 220                 }
 221                 // The new fd is created NOT close-on-exec,
 222                 // which is exactly what we want.
 223                 err1 = raw_dup2(fd[i], i)
 224                 if err1 != 0 {
 225                         goto childerror
 226                 }
 227         }
 228
 229         // By convention, we don't close-on-exec the fds we are
 230         // started with, so if len(fd) < 3, close 0, 1, 2 as needed.
 231         // Programs that know they inherit fds >= 3 will need
 232         // to set them close-on-exec.
 233         for i = len(fd); i < 3; i++ {
 234                 raw_close(i)
 235         }
 236
 237         // Detach fd 0 from tty
 238         if sys.Noctty {
 239                 _, err1 = raw_ioctl(0, TIOCNOTTY, 0)
 240                 if err1 != 0 {
 241                         goto childerror
 242                 }
 243         }
 244
 245         // Make fd 0 the tty
 246         if sys.Setctty && sys.Ctty >= 0 {
 247                 _, err1 = raw_ioctl(0, TIOCSCTTY, sys.Ctty)
 248                 if err1 != 0 {
 249                         goto childerror
 250                 }
 251         }
 252
 253         // Time to exec.
 254         err1 = raw_execve(argv0, &argv[0], &envv[0])
 255
 256 childerror:
 257         // send error code on pipe
 258         raw_write(pipe, (*byte)(unsafe.Pointer(&err1)), int(unsafe.Sizeof(err1)))
 259         for {
 260                 raw_exit(253)
 261         }
 262 }
 263
 264 // Try to open a pipe with O_CLOEXEC set on both file descriptors.
 265 func forkExecPipe(p []int) (err error) {
 266         err = Pipe2(p, O_CLOEXEC)
 267         // pipe2 was added in 2.6.27 and our minimum requirement is 2.6.23, so it
 268         // might not be implemented.
 269         if err == ENOSYS {
 270                 if err = Pipe(p); err != nil {
 271                         return
 272                 }
 273                 if _, err = fcntl(p[0], F_SETFD, FD_CLOEXEC); err != nil {
 274                         return
 275                 }
 276                 _, err = fcntl(p[1], F_SETFD, FD_CLOEXEC)
 277         }
 278         return
 279 }