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Source file src/syscall/exec_bsd.go

Documentation: syscall

     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 darwin dragonfly freebsd netbsd openbsd
     6  
     7  package syscall
     8  
     9  import (
    10  	"runtime"
    11  	"unsafe"
    12  )
    13  
    14  type SysProcAttr struct {
    15  	Chroot     string      // Chroot.
    16  	Credential *Credential // Credential.
    17  	Ptrace     bool        // Enable tracing.
    18  	Setsid     bool        // Create session.
    19  	Setpgid    bool        // Set process group ID to Pgid, or, if Pgid == 0, to new pid.
    20  	Setctty    bool        // Set controlling terminal to fd Ctty
    21  	Noctty     bool        // Detach fd 0 from controlling terminal
    22  	Ctty       int         // Controlling TTY fd
    23  	Foreground bool        // Place child's process group in foreground. (Implies Setpgid. Uses Ctty as fd of controlling TTY)
    24  	Pgid       int         // Child's process group ID if Setpgid.
    25  }
    26  
    27  // Implemented in runtime package.
    28  func runtime_BeforeFork()
    29  func runtime_AfterFork()
    30  func runtime_AfterForkInChild()
    31  
    32  // Fork, dup fd onto 0..len(fd), and exec(argv0, argvv, envv) in child.
    33  // If a dup or exec fails, write the errno error to pipe.
    34  // (Pipe is close-on-exec so if exec succeeds, it will be closed.)
    35  // In the child, this function must not acquire any locks, because
    36  // they might have been locked at the time of the fork. This means
    37  // no rescheduling, no malloc calls, and no new stack segments.
    38  // For the same reason compiler does not race instrument it.
    39  // The calls to RawSyscall are okay because they are assembly
    40  // functions that do not grow the stack.
    41  //go:norace
    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, r2 uintptr
    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  	darwin := runtime.GOOS == "darwin"
    66  
    67  	// About to call fork.
    68  	// No more allocation or calls of non-assembly functions.
    69  	runtime_BeforeFork()
    70  	r1, r2, err1 = RawSyscall(SYS_FORK, 0, 0, 0)
    71  	if err1 != 0 {
    72  		runtime_AfterFork()
    73  		return 0, err1
    74  	}
    75  
    76  	// On Darwin:
    77  	//	r1 = child pid in both parent and child.
    78  	//	r2 = 0 in parent, 1 in child.
    79  	// Convert to normal Unix r1 = 0 in child.
    80  	if darwin && r2 == 1 {
    81  		r1 = 0
    82  	}
    83  
    84  	if r1 != 0 {
    85  		// parent; return PID
    86  		runtime_AfterFork()
    87  		return int(r1), 0
    88  	}
    89  
    90  	// Fork succeeded, now in child.
    91  
    92  	runtime_AfterForkInChild()
    93  
    94  	// Enable tracing if requested.
    95  	if sys.Ptrace {
    96  		_, _, err1 = RawSyscall(SYS_PTRACE, uintptr(PTRACE_TRACEME), 0, 0)
    97  		if err1 != 0 {
    98  			goto childerror
    99  		}
   100  	}
   101  
   102  	// Session ID
   103  	if sys.Setsid {
   104  		_, _, err1 = RawSyscall(SYS_SETSID, 0, 0, 0)
   105  		if err1 != 0 {
   106  			goto childerror
   107  		}
   108  	}
   109  
   110  	// Set process group
   111  	if sys.Setpgid || sys.Foreground {
   112  		// Place child in process group.
   113  		_, _, err1 = RawSyscall(SYS_SETPGID, 0, uintptr(sys.Pgid), 0)
   114  		if err1 != 0 {
   115  			goto childerror
   116  		}
   117  	}
   118  
   119  	if sys.Foreground {
   120  		pgrp := sys.Pgid
   121  		if pgrp == 0 {
   122  			r1, _, err1 = RawSyscall(SYS_GETPID, 0, 0, 0)
   123  			if err1 != 0 {
   124  				goto childerror
   125  			}
   126  
   127  			pgrp = int(r1)
   128  		}
   129  
   130  		// Place process group in foreground.
   131  		_, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSPGRP), uintptr(unsafe.Pointer(&pgrp)))
   132  		if err1 != 0 {
   133  			goto childerror
   134  		}
   135  	}
   136  
   137  	// Chroot
   138  	if chroot != nil {
   139  		_, _, err1 = RawSyscall(SYS_CHROOT, uintptr(unsafe.Pointer(chroot)), 0, 0)
   140  		if err1 != 0 {
   141  			goto childerror
   142  		}
   143  	}
   144  
   145  	// User and groups
   146  	if cred := sys.Credential; cred != nil {
   147  		ngroups := uintptr(len(cred.Groups))
   148  		groups := uintptr(0)
   149  		if ngroups > 0 {
   150  			groups = uintptr(unsafe.Pointer(&cred.Groups[0]))
   151  		}
   152  		if !cred.NoSetGroups {
   153  			_, _, err1 = RawSyscall(SYS_SETGROUPS, ngroups, groups, 0)
   154  			if err1 != 0 {
   155  				goto childerror
   156  			}
   157  		}
   158  		_, _, err1 = RawSyscall(SYS_SETGID, uintptr(cred.Gid), 0, 0)
   159  		if err1 != 0 {
   160  			goto childerror
   161  		}
   162  		_, _, err1 = RawSyscall(SYS_SETUID, uintptr(cred.Uid), 0, 0)
   163  		if err1 != 0 {
   164  			goto childerror
   165  		}
   166  	}
   167  
   168  	// Chdir
   169  	if dir != nil {
   170  		_, _, err1 = RawSyscall(SYS_CHDIR, uintptr(unsafe.Pointer(dir)), 0, 0)
   171  		if err1 != 0 {
   172  			goto childerror
   173  		}
   174  	}
   175  
   176  	// Pass 1: look for fd[i] < i and move those up above len(fd)
   177  	// so that pass 2 won't stomp on an fd it needs later.
   178  	if pipe < nextfd {
   179  		_, _, err1 = RawSyscall(SYS_DUP2, uintptr(pipe), uintptr(nextfd), 0)
   180  		if err1 != 0 {
   181  			goto childerror
   182  		}
   183  		RawSyscall(SYS_FCNTL, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
   184  		pipe = nextfd
   185  		nextfd++
   186  	}
   187  	for i = 0; i < len(fd); i++ {
   188  		if fd[i] >= 0 && fd[i] < int(i) {
   189  			if nextfd == pipe { // don't stomp on pipe
   190  				nextfd++
   191  			}
   192  			_, _, err1 = RawSyscall(SYS_DUP2, uintptr(fd[i]), uintptr(nextfd), 0)
   193  			if err1 != 0 {
   194  				goto childerror
   195  			}
   196  			RawSyscall(SYS_FCNTL, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
   197  			fd[i] = nextfd
   198  			nextfd++
   199  		}
   200  	}
   201  
   202  	// Pass 2: dup fd[i] down onto i.
   203  	for i = 0; i < len(fd); i++ {
   204  		if fd[i] == -1 {
   205  			RawSyscall(SYS_CLOSE, uintptr(i), 0, 0)
   206  			continue
   207  		}
   208  		if fd[i] == int(i) {
   209  			// dup2(i, i) won't clear close-on-exec flag on Linux,
   210  			// probably not elsewhere either.
   211  			_, _, err1 = RawSyscall(SYS_FCNTL, uintptr(fd[i]), F_SETFD, 0)
   212  			if err1 != 0 {
   213  				goto childerror
   214  			}
   215  			continue
   216  		}
   217  		// The new fd is created NOT close-on-exec,
   218  		// which is exactly what we want.
   219  		_, _, err1 = RawSyscall(SYS_DUP2, uintptr(fd[i]), uintptr(i), 0)
   220  		if err1 != 0 {
   221  			goto childerror
   222  		}
   223  	}
   224  
   225  	// By convention, we don't close-on-exec the fds we are
   226  	// started with, so if len(fd) < 3, close 0, 1, 2 as needed.
   227  	// Programs that know they inherit fds >= 3 will need
   228  	// to set them close-on-exec.
   229  	for i = len(fd); i < 3; i++ {
   230  		RawSyscall(SYS_CLOSE, uintptr(i), 0, 0)
   231  	}
   232  
   233  	// Detach fd 0 from tty
   234  	if sys.Noctty {
   235  		_, _, err1 = RawSyscall(SYS_IOCTL, 0, uintptr(TIOCNOTTY), 0)
   236  		if err1 != 0 {
   237  			goto childerror
   238  		}
   239  	}
   240  
   241  	// Set the controlling TTY to Ctty
   242  	if sys.Setctty {
   243  		_, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSCTTY), 0)
   244  		if err1 != 0 {
   245  			goto childerror
   246  		}
   247  	}
   248  
   249  	// Time to exec.
   250  	_, _, err1 = RawSyscall(SYS_EXECVE,
   251  		uintptr(unsafe.Pointer(argv0)),
   252  		uintptr(unsafe.Pointer(&argv[0])),
   253  		uintptr(unsafe.Pointer(&envv[0])))
   254  
   255  childerror:
   256  	// send error code on pipe
   257  	RawSyscall(SYS_WRITE, uintptr(pipe), uintptr(unsafe.Pointer(&err1)), unsafe.Sizeof(err1))
   258  	for {
   259  		RawSyscall(SYS_EXIT, 253, 0, 0)
   260  	}
   261  }
   262  

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