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// Package syscallcompat wraps Linux-specific syscalls.
package syscallcompat
import (
"fmt"
"runtime"
"sync"
"syscall"
"golang.org/x/sys/unix"
"github.com/hanwen/go-fuse/fuse"
"github.com/rfjakob/gocryptfs/internal/tlog"
)
const (
_FALLOC_FL_KEEP_SIZE = 0x01
// O_DIRECT means oncached I/O on Linux. No direct equivalent on MacOS and defined
// to zero there.
O_DIRECT = syscall.O_DIRECT
// O_PATH is only defined on Linux
O_PATH = unix.O_PATH
)
var preallocWarn sync.Once
// EnospcPrealloc preallocates ciphertext space without changing the file
// size. This guarantees that we don't run out of space while writing a
// ciphertext block (that would corrupt the block).
func EnospcPrealloc(fd int, off int64, len int64) (err error) {
for {
err = syscall.Fallocate(fd, _FALLOC_FL_KEEP_SIZE, off, len)
if err == syscall.EINTR {
// fallocate, like many syscalls, can return EINTR. This is not an
// error and just signifies that the operation was interrupted by a
// signal and we should try again.
continue
}
if err == syscall.EOPNOTSUPP {
// ZFS and ext3 do not support fallocate. Warn but continue anyway.
// https://github.com/rfjakob/gocryptfs/issues/22
preallocWarn.Do(func() {
tlog.Warn.Printf("Warning: The underlying filesystem " +
"does not support fallocate(2). gocryptfs will continue working " +
"but is no longer resistant against out-of-space errors.\n")
})
return nil
}
return err
}
}
// Fallocate wraps the Fallocate syscall.
func Fallocate(fd int, mode uint32, off int64, len int64) (err error) {
return syscall.Fallocate(fd, mode, off, len)
}
// OpenatUser runs the Openat syscall in the context of a different user.
func OpenatUser(dirfd int, path string, flags int, mode uint32, context *fuse.Context) (fd int, err error) {
if context != nil {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
err = syscall.Setregid(-1, int(context.Owner.Gid))
if err != nil {
return -1, err
}
defer syscall.Setregid(-1, 0)
err = syscall.Setreuid(-1, int(context.Owner.Uid))
if err != nil {
return -1, err
}
defer syscall.Setreuid(-1, 0)
}
return Openat(dirfd, path, flags, mode)
}
// Mknodat wraps the Mknodat syscall.
func Mknodat(dirfd int, path string, mode uint32, dev int) (err error) {
return syscall.Mknodat(dirfd, path, mode, dev)
}
// MknodatUser runs the Mknodat syscall in the context of a different user.
func MknodatUser(dirfd int, path string, mode uint32, dev int, context *fuse.Context) (err error) {
if context != nil {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
err = syscall.Setregid(-1, int(context.Owner.Gid))
if err != nil {
return err
}
defer syscall.Setregid(-1, 0)
err = syscall.Setreuid(-1, int(context.Owner.Uid))
if err != nil {
return err
}
defer syscall.Setreuid(-1, 0)
}
return Mknodat(dirfd, path, mode, dev)
}
// Dup3 wraps the Dup3 syscall. We want to use Dup3 rather than Dup2 because Dup2
// is not implemented on arm64.
func Dup3(oldfd int, newfd int, flags int) (err error) {
return syscall.Dup3(oldfd, newfd, flags)
}
// Fchmodat syscall.
func Fchmodat(dirfd int, path string, mode uint32, flags int) (err error) {
// Linux does not support passing flags to Fchmodat! From the man page:
// AT_SYMLINK_NOFOLLOW ... This flag is not currently implemented.
// Linux ignores any flags, but Go stdlib rejects them with EOPNOTSUPP starting
// with Go 1.11. See https://github.com/golang/go/issues/20130 for more info.
// TODO: Use fchmodat2 once available on Linux.
// Why would we ever want to call this without AT_SYMLINK_NOFOLLOW?
if flags&unix.AT_SYMLINK_NOFOLLOW == 0 {
tlog.Warn.Printf("Fchmodat: adding missing AT_SYMLINK_NOFOLLOW flag")
}
// Open handle to the filename (but without opening the actual file).
fd, err := syscall.Openat(dirfd, path, syscall.O_NOFOLLOW|O_PATH, 0)
if err != nil {
return err
}
defer syscall.Close(fd)
// Now we can check the type without the risk of race-conditions.
var st syscall.Stat_t
err = syscall.Fstat(fd, &st)
if err != nil {
return err
}
// Return syscall.ELOOP if path refers to a symlink.
var a fuse.Attr
a.FromStat(&st)
if a.IsSymlink() {
return syscall.ELOOP
}
// Change mode of the actual file. Note that we can neither use
// Fchmodat (since fd is not necessarily a directory) nor Fchmod
// (since we are using O_PATH).
procPath := fmt.Sprintf("/proc/self/fd/%d", fd)
return syscall.Chmod(procPath, mode)
}
// SymlinkatUser runs the Symlinkat syscall in the context of a different user.
func SymlinkatUser(oldpath string, newdirfd int, newpath string, context *fuse.Context) (err error) {
if context != nil {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
err = syscall.Setregid(-1, int(context.Owner.Gid))
if err != nil {
return err
}
defer syscall.Setregid(-1, 0)
err = syscall.Setreuid(-1, int(context.Owner.Uid))
if err != nil {
return err
}
defer syscall.Setreuid(-1, 0)
}
return Symlinkat(oldpath, newdirfd, newpath)
}
// MkdiratUser runs the Mkdirat syscall in the context of a different user.
func MkdiratUser(dirfd int, path string, mode uint32, context *fuse.Context) (err error) {
if context != nil {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
err = syscall.Setregid(-1, int(context.Owner.Gid))
if err != nil {
return err
}
defer syscall.Setregid(-1, 0)
err = syscall.Setreuid(-1, int(context.Owner.Uid))
if err != nil {
return err
}
defer syscall.Setreuid(-1, 0)
}
return Mkdirat(dirfd, path, mode)
}
// Getdents syscall.
func Getdents(fd int) ([]fuse.DirEntry, error) {
return getdents(fd)
}
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