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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)
}
// FchmodatNofollow is like Fchmodat but never follows symlinks.
//
// This should be handled by the AT_SYMLINK_NOFOLLOW flag, but Linux
// does not implement it, so we have to perform an elaborate dance
// with O_PATH and /proc/self/fd.
//
// See also: Qemu implemented the same logic as fchmodat_nofollow():
// https://git.qemu.org/?p=qemu.git;a=blob;f=hw/9pfs/9p-local.c#l335
func FchmodatNofollow(dirfd int, path string, mode uint32) (err error) {
// Open handle to the filename (but without opening the actual file).
// This succeeds even when we don't have read permissions to the 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.
// Return syscall.ELOOP if it is a symlink.
var st syscall.Stat_t
err = syscall.Fstat(fd, &st)
if err != nil {
return err
}
if st.Mode&syscall.S_IFMT == syscall.S_IFLNK {
return syscall.ELOOP
}
// Change mode of the actual file. Fchmod does not work with O_PATH,
// but Chmod via /proc/self/fd works.
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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