github.com/stolowski/snapd@v0.0.0-20210407085831-115137ce5a22/osutil/sys/syscall.go (about)

     1  // -*- Mode: Go; indent-tabs-mode: t -*-
     2  
     3  /*
     4   * Copyright (C) 2017 Canonical Ltd
     5   *
     6   * This program is free software: you can redistribute it and/or modify
     7   * it under the terms of the GNU General Public License version 3 as
     8   * published by the Free Software Foundation.
     9   *
    10   * This program is distributed in the hope that it will be useful,
    11   * but WITHOUT ANY WARRANTY; without even the implied warranty of
    12   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    13   * GNU General Public License for more details.
    14   *
    15   * You should have received a copy of the GNU General Public License
    16   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
    17   *
    18   */
    19  
    20  package sys
    21  
    22  import (
    23  	"os"
    24  	"syscall"
    25  	"unsafe"
    26  )
    27  
    28  // FlagID can be passed to chown-ish functions to mean "no change",
    29  // and can be returned from getuid-ish functions to mean "not found".
    30  const FlagID = 1<<32 - 1
    31  
    32  // UserID is the type of the system's user identifiers (in C, uid_t).
    33  //
    34  // We give it its own explicit type so you don't have to remember that
    35  // it's a uint32 (which lead to the bug this package fixes in the
    36  // first place)
    37  type UserID uint32
    38  
    39  // GroupID is the type of the system's group identifiers (in C, gid_t).
    40  type GroupID uint32
    41  
    42  // uid_t is an unsigned 32-bit integer in linux right now.
    43  // so syscall.Gete?[ug]id are wrong, and break in 32 bits
    44  // (see https://github.com/golang/go/issues/22739)
    45  func Getuid() UserID {
    46  	return UserID(getid(_SYS_GETUID))
    47  }
    48  
    49  func Geteuid() UserID {
    50  	return UserID(getid(_SYS_GETEUID))
    51  }
    52  
    53  func Getgid() GroupID {
    54  	return GroupID(getid(_SYS_GETGID))
    55  }
    56  
    57  func Getegid() GroupID {
    58  	return GroupID(getid(_SYS_GETEGID))
    59  }
    60  
    61  func getid(id uintptr) uint32 {
    62  	// these are documented as not failing, but see golang#22924
    63  	r0, _, errno := syscall.RawSyscall(id, 0, 0, 0)
    64  	if errno != 0 {
    65  		return uint32(-errno)
    66  	}
    67  	return uint32(r0)
    68  }
    69  
    70  func Chown(f *os.File, uid UserID, gid GroupID) error {
    71  	return Fchown(int(f.Fd()), uid, gid)
    72  }
    73  
    74  func Fchown(fd int, uid UserID, gid GroupID) error {
    75  	_, _, errno := syscall.Syscall(syscall.SYS_FCHOWN, uintptr(fd), uintptr(uid), uintptr(gid))
    76  	if errno == 0 {
    77  		return nil
    78  	}
    79  	return errno
    80  }
    81  
    82  func ChownPath(path string, uid UserID, gid GroupID) error {
    83  	AT_FDCWD := -100 // also written as -0x64 in ztypes_linux_*.go (but -100 in sys_linux_*.s, and /usr/include/linux/fcntl.h)
    84  	return FchownAt(uintptr(AT_FDCWD), path, uid, gid, 0)
    85  }
    86  
    87  func FchownAt(dirfd uintptr, path string, uid UserID, gid GroupID, flags int) error {
    88  	p0, err := syscall.BytePtrFromString(path)
    89  	if err != nil {
    90  		return err
    91  	}
    92  	_, _, errno := syscall.Syscall6(_SYS_FCHOWNAT, dirfd, uintptr(unsafe.Pointer(p0)), uintptr(uid), uintptr(gid), uintptr(flags), 0)
    93  	if errno == 0 {
    94  		return nil
    95  	}
    96  	return errno
    97  }
    98  
    99  // As of Go 1.9, the O_PATH constant does not seem to be declared
   100  // uniformly over all archtiectures.
   101  const O_PATH = 0x200000
   102  
   103  func FcntlGetFl(fd int) (int, error) {
   104  	flags, _, errno := syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), uintptr(syscall.F_GETFL), 0)
   105  	if errno != 0 {
   106  		return 0, errno
   107  	}
   108  	return int(flags), nil
   109  }