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  //go:build dragonfly || netbsd || (openbsd && mips64)
     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 sets the process group ID of the child to Pgid,
    20  	// or, if Pgid == 0, to the new child's process ID.
    21  	Setpgid bool
    22  	// Setctty sets the controlling terminal of the child to
    23  	// file descriptor Ctty. Ctty must be a descriptor number
    24  	// in the child process: an index into ProcAttr.Files.
    25  	// This is only meaningful if Setsid is true.
    26  	Setctty bool
    27  	Noctty  bool // Detach fd 0 from controlling terminal
    28  	Ctty    int  // Controlling TTY fd
    29  	// Foreground places the child process group in the foreground.
    30  	// This implies Setpgid. The Ctty field must be set to
    31  	// the descriptor of the controlling TTY.
    32  	// Unlike Setctty, in this case Ctty must be a descriptor
    33  	// number in the parent process.
    34  	Foreground bool
    35  	Pgid       int // Child's process group ID if Setpgid.
    36  }
    37  
    38  // Implemented in runtime package.
    39  func runtime_BeforeFork()
    40  func runtime_AfterFork()
    41  func runtime_AfterForkInChild()
    42  
    43  // Fork, dup fd onto 0..len(fd), and exec(argv0, argvv, envv) in child.
    44  // If a dup or exec fails, write the errno error to pipe.
    45  // (Pipe is close-on-exec so if exec succeeds, it will be closed.)
    46  // In the child, this function must not acquire any locks, because
    47  // they might have been locked at the time of the fork. This means
    48  // no rescheduling, no malloc calls, and no new stack segments.
    49  // For the same reason compiler does not race instrument it.
    50  // The calls to RawSyscall are okay because they are assembly
    51  // functions that do not grow the stack.
    52  //
    53  //go:norace
    54  func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr *ProcAttr, sys *SysProcAttr, pipe int) (pid int, err Errno) {
    55  	// Declare all variables at top in case any
    56  	// declarations require heap allocation (e.g., err1).
    57  	var (
    58  		r1              uintptr
    59  		err1            Errno
    60  		nextfd          int
    61  		i               int
    62  		pgrp            _C_int
    63  		cred            *Credential
    64  		ngroups, groups uintptr
    65  	)
    66  
    67  	rlim := origRlimitNofile.Load()
    68  
    69  	// guard against side effects of shuffling fds below.
    70  	// Make sure that nextfd is beyond any currently open files so
    71  	// that we can't run the risk of overwriting any of them.
    72  	fd := make([]int, len(attr.Files))
    73  	nextfd = len(attr.Files)
    74  	for i, ufd := range attr.Files {
    75  		if nextfd < int(ufd) {
    76  			nextfd = int(ufd)
    77  		}
    78  		fd[i] = int(ufd)
    79  	}
    80  	nextfd++
    81  
    82  	// About to call fork.
    83  	// No more allocation or calls of non-assembly functions.
    84  	runtime_BeforeFork()
    85  	r1, _, err1 = RawSyscall(SYS_FORK, 0, 0, 0)
    86  	if err1 != 0 {
    87  		runtime_AfterFork()
    88  		return 0, err1
    89  	}
    90  
    91  	if r1 != 0 {
    92  		// parent; return PID
    93  		runtime_AfterFork()
    94  		return int(r1), 0
    95  	}
    96  
    97  	// Fork succeeded, now in child.
    98  
    99  	// Enable tracing if requested.
   100  	if sys.Ptrace {
   101  		_, _, err1 = RawSyscall(SYS_PTRACE, uintptr(PTRACE_TRACEME), 0, 0)
   102  		if err1 != 0 {
   103  			goto childerror
   104  		}
   105  	}
   106  
   107  	// Session ID
   108  	if sys.Setsid {
   109  		_, _, err1 = RawSyscall(SYS_SETSID, 0, 0, 0)
   110  		if err1 != 0 {
   111  			goto childerror
   112  		}
   113  	}
   114  
   115  	// Set process group
   116  	if sys.Setpgid || sys.Foreground {
   117  		// Place child in process group.
   118  		_, _, err1 = RawSyscall(SYS_SETPGID, 0, uintptr(sys.Pgid), 0)
   119  		if err1 != 0 {
   120  			goto childerror
   121  		}
   122  	}
   123  
   124  	if sys.Foreground {
   125  		// This should really be pid_t, however _C_int (aka int32) is
   126  		// generally equivalent.
   127  		pgrp = _C_int(sys.Pgid)
   128  		if pgrp == 0 {
   129  			r1, _, err1 = RawSyscall(SYS_GETPID, 0, 0, 0)
   130  			if err1 != 0 {
   131  				goto childerror
   132  			}
   133  
   134  			pgrp = _C_int(r1)
   135  		}
   136  
   137  		// Place process group in foreground.
   138  		_, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSPGRP), uintptr(unsafe.Pointer(&pgrp)))
   139  		if err1 != 0 {
   140  			goto childerror
   141  		}
   142  	}
   143  
   144  	// Restore the signal mask. We do this after TIOCSPGRP to avoid
   145  	// having the kernel send a SIGTTOU signal to the process group.
   146  	runtime_AfterForkInChild()
   147  
   148  	// Chroot
   149  	if chroot != nil {
   150  		_, _, err1 = RawSyscall(SYS_CHROOT, uintptr(unsafe.Pointer(chroot)), 0, 0)
   151  		if err1 != 0 {
   152  			goto childerror
   153  		}
   154  	}
   155  
   156  	// User and groups
   157  	if cred = sys.Credential; cred != nil {
   158  		ngroups = uintptr(len(cred.Groups))
   159  		groups = uintptr(0)
   160  		if ngroups > 0 {
   161  			groups = uintptr(unsafe.Pointer(&cred.Groups[0]))
   162  		}
   163  		if !cred.NoSetGroups {
   164  			_, _, err1 = RawSyscall(SYS_SETGROUPS, ngroups, groups, 0)
   165  			if err1 != 0 {
   166  				goto childerror
   167  			}
   168  		}
   169  		_, _, err1 = RawSyscall(SYS_SETGID, uintptr(cred.Gid), 0, 0)
   170  		if err1 != 0 {
   171  			goto childerror
   172  		}
   173  		_, _, err1 = RawSyscall(SYS_SETUID, uintptr(cred.Uid), 0, 0)
   174  		if err1 != 0 {
   175  			goto childerror
   176  		}
   177  	}
   178  
   179  	// Chdir
   180  	if dir != nil {
   181  		_, _, err1 = RawSyscall(SYS_CHDIR, uintptr(unsafe.Pointer(dir)), 0, 0)
   182  		if err1 != 0 {
   183  			goto childerror
   184  		}
   185  	}
   186  
   187  	// Pass 1: look for fd[i] < i and move those up above len(fd)
   188  	// so that pass 2 won't stomp on an fd it needs later.
   189  	if pipe < nextfd {
   190  		if runtime.GOOS == "netbsd" || (runtime.GOOS == "openbsd" && runtime.GOARCH == "mips64") {
   191  			_, _, err1 = RawSyscall(_SYS_DUP3, uintptr(pipe), uintptr(nextfd), O_CLOEXEC)
   192  		} else if runtime.GOOS == "dragonfly" {
   193  			_, _, err1 = RawSyscall(SYS_FCNTL, uintptr(pipe), _F_DUP2FD_CLOEXEC, uintptr(nextfd))
   194  		} else {
   195  			_, _, err1 = RawSyscall(SYS_DUP2, uintptr(pipe), uintptr(nextfd), 0)
   196  			if err1 != 0 {
   197  				goto childerror
   198  			}
   199  			_, _, err1 = RawSyscall(SYS_FCNTL, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
   200  		}
   201  		if err1 != 0 {
   202  			goto childerror
   203  		}
   204  		pipe = nextfd
   205  		nextfd++
   206  	}
   207  	for i = 0; i < len(fd); i++ {
   208  		if fd[i] >= 0 && fd[i] < i {
   209  			if nextfd == pipe { // don't stomp on pipe
   210  				nextfd++
   211  			}
   212  			if runtime.GOOS == "netbsd" || (runtime.GOOS == "openbsd" && runtime.GOARCH == "mips64") {
   213  				_, _, err1 = RawSyscall(_SYS_DUP3, uintptr(fd[i]), uintptr(nextfd), O_CLOEXEC)
   214  			} else if runtime.GOOS == "dragonfly" {
   215  				_, _, err1 = RawSyscall(SYS_FCNTL, uintptr(fd[i]), _F_DUP2FD_CLOEXEC, uintptr(nextfd))
   216  			} else {
   217  				_, _, err1 = RawSyscall(SYS_DUP2, uintptr(fd[i]), uintptr(nextfd), 0)
   218  				if err1 != 0 {
   219  					goto childerror
   220  				}
   221  				_, _, err1 = RawSyscall(SYS_FCNTL, uintptr(nextfd), F_SETFD, FD_CLOEXEC)
   222  			}
   223  			if err1 != 0 {
   224  				goto childerror
   225  			}
   226  			fd[i] = nextfd
   227  			nextfd++
   228  		}
   229  	}
   230  
   231  	// Pass 2: dup fd[i] down onto i.
   232  	for i = 0; i < len(fd); i++ {
   233  		if fd[i] == -1 {
   234  			RawSyscall(SYS_CLOSE, uintptr(i), 0, 0)
   235  			continue
   236  		}
   237  		if fd[i] == i {
   238  			// dup2(i, i) won't clear close-on-exec flag on Linux,
   239  			// probably not elsewhere either.
   240  			_, _, err1 = RawSyscall(SYS_FCNTL, uintptr(fd[i]), F_SETFD, 0)
   241  			if err1 != 0 {
   242  				goto childerror
   243  			}
   244  			continue
   245  		}
   246  		// The new fd is created NOT close-on-exec,
   247  		// which is exactly what we want.
   248  		_, _, err1 = RawSyscall(SYS_DUP2, uintptr(fd[i]), uintptr(i), 0)
   249  		if err1 != 0 {
   250  			goto childerror
   251  		}
   252  	}
   253  
   254  	// By convention, we don't close-on-exec the fds we are
   255  	// started with, so if len(fd) < 3, close 0, 1, 2 as needed.
   256  	// Programs that know they inherit fds >= 3 will need
   257  	// to set them close-on-exec.
   258  	for i = len(fd); i < 3; i++ {
   259  		RawSyscall(SYS_CLOSE, uintptr(i), 0, 0)
   260  	}
   261  
   262  	// Detach fd 0 from tty
   263  	if sys.Noctty {
   264  		_, _, err1 = RawSyscall(SYS_IOCTL, 0, uintptr(TIOCNOTTY), 0)
   265  		if err1 != 0 {
   266  			goto childerror
   267  		}
   268  	}
   269  
   270  	// Set the controlling TTY to Ctty
   271  	if sys.Setctty {
   272  		_, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSCTTY), 0)
   273  		if err1 != 0 {
   274  			goto childerror
   275  		}
   276  	}
   277  
   278  	// Restore original rlimit.
   279  	if rlim != nil {
   280  		RawSyscall(SYS_SETRLIMIT, uintptr(RLIMIT_NOFILE), uintptr(unsafe.Pointer(rlim)), 0)
   281  	}
   282  
   283  	// Time to exec.
   284  	_, _, err1 = RawSyscall(SYS_EXECVE,
   285  		uintptr(unsafe.Pointer(argv0)),
   286  		uintptr(unsafe.Pointer(&argv[0])),
   287  		uintptr(unsafe.Pointer(&envv[0])))
   288  
   289  childerror:
   290  	// send error code on pipe
   291  	RawSyscall(SYS_WRITE, uintptr(pipe), uintptr(unsafe.Pointer(&err1)), unsafe.Sizeof(err1))
   292  	for {
   293  		RawSyscall(SYS_EXIT, 253, 0, 0)
   294  	}
   295  }
   296  
   297  // forkAndExecFailureCleanup cleans up after an exec failure.
   298  func forkAndExecFailureCleanup(attr *ProcAttr, sys *SysProcAttr) {
   299  	// Nothing to do.
   300  }
   301
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