libgo/go/syscall/exec_unix.go

   1 // Copyright 2009 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 linux netbsd openbsd solaris
   6
   7 // Fork, exec, wait, etc.
   8
   9 package syscall
  10
  11 import (
  12         "runtime"
  13         "sync"
  14         "unsafe"
  15 )
  16
  17 //sysnb raw_fork() (pid Pid_t, err Errno)
  18 //fork() Pid_t
  19
  20 //sysnb raw_getpid() (pid Pid_t)
  21 //getpid() Pid_t
  22
  23 //sysnb raw_getppid() (pid Pid_t)
  24 //getppid() Pid_t
  25
  26 //sysnb raw_setsid() (err Errno)
  27 //setsid() Pid_t
  28
  29 //sysnb raw_setpgid(pid int, pgid int) (err Errno)
  30 //setpgid(pid Pid_t, pgid Pid_t) _C_int
  31
  32 //sysnb raw_chroot(path *byte) (err Errno)
  33 //chroot(path *byte) _C_int
  34
  35 //sysnb raw_chdir(path *byte) (err Errno)
  36 //chdir(path *byte) _C_int
  37
  38 //sysnb raw_fcntl(fd int, cmd int, arg int) (val int, err Errno)
  39 //__go_fcntl(fd _C_int, cmd _C_int, arg _C_int) _C_int
  40
  41 //sysnb raw_close(fd int) (err Errno)
  42 //close(fd _C_int) _C_int
  43
  44 //sysnb raw_ioctl(fd int, cmd uintptr, val int) (rval int, err Errno)
  45 //__go_ioctl(fd _C_int, cmd _C_int, val _C_int) _C_int
  46
  47 //sysnb raw_ioctl_ptr(fd int, cmd uintptr, val unsafe.Pointer) (rval int, err Errno)
  48 //__go_ioctl_ptr(fd _C_int, cmd _C_int, val unsafe.Pointer) _C_int
  49
  50 //sysnb raw_execve(argv0 *byte, argv **byte, envv **byte) (err Errno)
  51 //execve(argv0 *byte, argv **byte, envv **byte) _C_int
  52
  53 //sysnb raw_write(fd int, buf *byte, count int) (err Errno)
  54 //write(fd _C_int, buf *byte, count Size_t) Ssize_t
  55
  56 //sysnb raw_exit(status int)
  57 //_exit(status _C_int)
  58
  59 //sysnb raw_dup2(oldfd int, newfd int) (err Errno)
  60 //dup2(oldfd _C_int, newfd _C_int) _C_int
  61
  62 //sysnb raw_kill(pid Pid_t, sig Signal) (err Errno)
  63 //kill(pid Pid_t, sig _C_int) _C_int
  64
  65 //sysnb raw_setgroups(size int, list unsafe.Pointer) (err Errno)
  66 //setgroups(size Size_t, list *Gid_t) _C_int
  67
  68 // Lock synchronizing creation of new file descriptors with fork.
  69 //
  70 // We want the child in a fork/exec sequence to inherit only the
  71 // file descriptors we intend. To do that, we mark all file
  72 // descriptors close-on-exec and then, in the child, explicitly
  73 // unmark the ones we want the exec'ed program to keep.
  74 // Unix doesn't make this easy: there is, in general, no way to
  75 // allocate a new file descriptor close-on-exec. Instead you
  76 // have to allocate the descriptor and then mark it close-on-exec.
  77 // If a fork happens between those two events, the child's exec
  78 // will inherit an unwanted file descriptor.
  79 //
  80 // This lock solves that race: the create new fd/mark close-on-exec
  81 // operation is done holding ForkLock for reading, and the fork itself
  82 // is done holding ForkLock for writing. At least, that's the idea.
  83 // There are some complications.
  84 //
  85 // Some system calls that create new file descriptors can block
  86 // for arbitrarily long times: open on a hung NFS server or named
  87 // pipe, accept on a socket, and so on. We can't reasonably grab
  88 // the lock across those operations.
  89 //
  90 // It is worse to inherit some file descriptors than others.
  91 // If a non-malicious child accidentally inherits an open ordinary file,
  92 // that's not a big deal. On the other hand, if a long-lived child
  93 // accidentally inherits the write end of a pipe, then the reader
  94 // of that pipe will not see EOF until that child exits, potentially
  95 // causing the parent program to hang. This is a common problem
  96 // in threaded C programs that use popen.
  97 //
  98 // Luckily, the file descriptors that are most important not to
  99 // inherit are not the ones that can take an arbitrarily long time
 100 // to create: pipe returns instantly, and the net package uses
 101 // non-blocking I/O to accept on a listening socket.
 102 // The rules for which file descriptor-creating operations use the
 103 // ForkLock are as follows:
 104 //
 105 // 1) Pipe. Does not block. Use the ForkLock.
 106 // 2) Socket. Does not block. Use the ForkLock.
 107 // 3) Accept. If using non-blocking mode, use the ForkLock.
 108 //             Otherwise, live with the race.
 109 // 4) Open. Can block. Use O_CLOEXEC if available (GNU/Linux).
 110 //             Otherwise, live with the race.
 111 // 5) Dup. Does not block. Use the ForkLock.
 112 //             On GNU/Linux, could use fcntl F_DUPFD_CLOEXEC
 113 //             instead of the ForkLock, but only for dup(fd, -1).
 114
 115 var ForkLock sync.RWMutex
 116
 117 // StringSlicePtr converts a slice of strings to a slice of pointers
 118 // to NUL-terminated byte arrays. If any string contains a NUL byte
 119 // this function panics instead of returning an error.
 120 //
 121 // Deprecated: Use SlicePtrFromStrings instead.
 122 func StringSlicePtr(ss []string) []*byte {
 123         bb := make([]*byte, len(ss)+1)
 124         for i := 0; i < len(ss); i++ {
 125                 bb[i] = StringBytePtr(ss[i])
 126         }
 127         bb[len(ss)] = nil
 128         return bb
 129 }
 130
 131 // SlicePtrFromStrings converts a slice of strings to a slice of
 132 // pointers to NUL-terminated byte arrays. If any string contains
 133 // a NUL byte, it returns (nil, EINVAL).
 134 func SlicePtrFromStrings(ss []string) ([]*byte, error) {
 135         var err error
 136         bb := make([]*byte, len(ss)+1)
 137         for i := 0; i < len(ss); i++ {
 138                 bb[i], err = BytePtrFromString(ss[i])
 139                 if err != nil {
 140                         return nil, err
 141                 }
 142         }
 143         bb[len(ss)] = nil
 144         return bb, nil
 145 }
 146
 147 func CloseOnExec(fd int) { fcntl(fd, F_SETFD, FD_CLOEXEC) }
 148
 149 func SetNonblock(fd int, nonblocking bool) (err error) {
 150         flag, err := fcntl(fd, F_GETFL, 0)
 151         if err != nil {
 152                 return err
 153         }
 154         if nonblocking {
 155                 flag |= O_NONBLOCK
 156         } else {
 157                 flag &^= O_NONBLOCK
 158         }
 159         _, err = fcntl(fd, F_SETFL, flag)
 160         return err
 161 }
 162
 163 // Credential holds user and group identities to be assumed
 164 // by a child process started by StartProcess.
 165 type Credential struct {
 166         Uid         uint32   // User ID.
 167         Gid         uint32   // Group ID.
 168         Groups      []uint32 // Supplementary group IDs.
 169         NoSetGroups bool     // If true, don't set supplementary groups
 170 }
 171
 172 // ProcAttr holds attributes that will be applied to a new process started
 173 // by StartProcess.
 174 type ProcAttr struct {
 175         Dir   string    // Current working directory.
 176         Env   []string  // Environment.
 177         Files []uintptr // File descriptors.
 178         Sys   *SysProcAttr
 179 }
 180
 181 var zeroProcAttr ProcAttr
 182 var zeroSysProcAttr SysProcAttr
 183
 184 func forkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err error) {
 185         var p [2]int
 186         var n int
 187         var err1 Errno
 188         var wstatus WaitStatus
 189
 190         if attr == nil {
 191                 attr = &zeroProcAttr
 192         }
 193         sys := attr.Sys
 194         if sys == nil {
 195                 sys = &zeroSysProcAttr
 196         }
 197
 198         p[0] = -1
 199         p[1] = -1
 200
 201         // Convert args to C form.
 202         argv0p, err := BytePtrFromString(argv0)
 203         if err != nil {
 204                 return 0, err
 205         }
 206         argvp, err := SlicePtrFromStrings(argv)
 207         if err != nil {
 208                 return 0, err
 209         }
 210         envvp, err := SlicePtrFromStrings(attr.Env)
 211         if err != nil {
 212                 return 0, err
 213         }
 214
 215         if (runtime.GOOS == "freebsd" || runtime.GOOS == "dragonfly") && len(argv[0]) > len(argv0) {
 216                 argvp[0] = argv0p
 217         }
 218
 219         var chroot *byte
 220         if sys.Chroot != "" {
 221                 chroot, err = BytePtrFromString(sys.Chroot)
 222                 if err != nil {
 223                         return 0, err
 224                 }
 225         }
 226         var dir *byte
 227         if attr.Dir != "" {
 228                 dir, err = BytePtrFromString(attr.Dir)
 229                 if err != nil {
 230                         return 0, err
 231                 }
 232         }
 233
 234         // Acquire the fork lock so that no other threads
 235         // create new fds that are not yet close-on-exec
 236         // before we fork.
 237         ForkLock.Lock()
 238
 239         // Allocate child status pipe close on exec.
 240         if err = forkExecPipe(p[:]); err != nil {
 241                 goto error
 242         }
 243
 244         // Kick off child.
 245         pid, err1 = forkAndExecInChild(argv0p, argvp, envvp, chroot, dir, attr, sys, p[1])
 246         if err1 != 0 {
 247                 err = Errno(err1)
 248                 goto error
 249         }
 250         ForkLock.Unlock()
 251
 252         // Read child error status from pipe.
 253         Close(p[1])
 254         n, err = readlen(p[0], (*byte)(unsafe.Pointer(&err1)), int(unsafe.Sizeof(err1)))
 255         Close(p[0])
 256         if err != nil || n != 0 {
 257                 if n == int(unsafe.Sizeof(err1)) {
 258                         err = Errno(err1)
 259                 }
 260                 if err == nil {
 261                         err = EPIPE
 262                 }
 263
 264                 // Child failed; wait for it to exit, to make sure
 265                 // the zombies don't accumulate.
 266                 _, err1 := Wait4(pid, &wstatus, 0, nil)
 267                 for err1 == EINTR {
 268                         _, err1 = Wait4(pid, &wstatus, 0, nil)
 269                 }
 270                 return 0, err
 271         }
 272
 273         // Read got EOF, so pipe closed on exec, so exec succeeded.
 274         return pid, nil
 275
 276 error:
 277         if p[0] >= 0 {
 278                 Close(p[0])
 279                 Close(p[1])
 280         }
 281         ForkLock.Unlock()
 282         return 0, err
 283 }
 284
 285 // Combination of fork and exec, careful to be thread safe.
 286 func ForkExec(argv0 string, argv []string, attr *ProcAttr) (pid int, err error) {
 287         return forkExec(argv0, argv, attr)
 288 }
 289
 290 // StartProcess wraps ForkExec for package os.
 291 func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, handle uintptr, err error) {
 292         pid, err = forkExec(argv0, argv, attr)
 293         return pid, 0, err
 294 }
 295
 296 // Implemented in runtime package.
 297 func runtime_BeforeExec()
 298 func runtime_AfterExec()
 299
 300 // execveSolaris is non-nil on Solaris, set to execve in exec_solaris.go; this
 301 // avoids a build dependency for other platforms.
 302 var execveSolaris func(path uintptr, argv uintptr, envp uintptr) (err Errno)
 303
 304 // Exec invokes the execve(2) system call.
 305 func Exec(argv0 string, argv []string, envv []string) (err error) {
 306         argv0p, err := BytePtrFromString(argv0)
 307         if err != nil {
 308                 return err
 309         }
 310         argvp, err := SlicePtrFromStrings(argv)
 311         if err != nil {
 312                 return err
 313         }
 314         envvp, err := SlicePtrFromStrings(envv)
 315         if err != nil {
 316                 return err
 317         }
 318         runtime_BeforeExec()
 319
 320         err1 := raw_execve(argv0p, &argvp[0], &envvp[0])
 321         runtime_AfterExec()
 322         return Errno(err1)
 323 }