95 lines
2.9 KiB
Go
95 lines
2.9 KiB
Go
package nametransform
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import (
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"bytes"
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"fmt"
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"io"
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"os"
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"syscall"
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"github.com/rfjakob/gocryptfs/internal/cryptocore"
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"github.com/rfjakob/gocryptfs/internal/syscallcompat"
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"github.com/rfjakob/gocryptfs/internal/tlog"
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)
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const (
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// DirIVLen is identical to AES block size
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DirIVLen = 16
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// DirIVFilename is the filename used to store directory IV.
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// Exported because we have to ignore this name in directory listing.
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DirIVFilename = "gocryptfs.diriv"
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)
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// ReadDirIVAt reads "gocryptfs.diriv" from the directory that is opened as "dirfd".
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// Using the dirfd makes it immune to concurrent renames of the directory.
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// Retries on EINTR.
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func ReadDirIVAt(dirfd int) (iv []byte, err error) {
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fdRaw, err := syscallcompat.Openat(dirfd, DirIVFilename,
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syscall.O_RDONLY|syscall.O_NOFOLLOW, 0)
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if err != nil {
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return nil, err
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}
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fd := os.NewFile(uintptr(fdRaw), DirIVFilename)
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defer fd.Close()
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return fdReadDirIV(fd)
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}
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// allZeroDirIV is preallocated to quickly check if the data read from disk is all zero
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var allZeroDirIV = make([]byte, DirIVLen)
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// fdReadDirIV reads and verifies the DirIV from an opened gocryptfs.diriv file.
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func fdReadDirIV(fd *os.File) (iv []byte, err error) {
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// We want to detect if the file is bigger than DirIVLen, so
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// make the buffer 1 byte bigger than necessary.
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iv = make([]byte, DirIVLen+1)
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n, err := fd.Read(iv)
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if err != nil && err != io.EOF {
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return nil, fmt.Errorf("read failed: %v", err)
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}
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iv = iv[0:n]
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if len(iv) != DirIVLen {
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return nil, fmt.Errorf("wanted %d bytes, got %d", DirIVLen, len(iv))
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}
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if bytes.Equal(iv, allZeroDirIV) {
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return nil, fmt.Errorf("diriv is all-zero")
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}
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return iv, nil
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}
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// WriteDirIVAt - create a new gocryptfs.diriv file in the directory opened at
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// "dirfd". On error we try to delete the incomplete file.
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// This function is exported because it is used from fusefrontend, main,
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// and also the automated tests.
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func WriteDirIVAt(dirfd int) error {
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iv := cryptocore.RandBytes(DirIVLen)
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// 0400 permissions: gocryptfs.diriv should never be modified after creation.
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// Don't use "ioutil.WriteFile", it causes trouble on NFS:
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// https://github.com/rfjakob/gocryptfs/commit/7d38f80a78644c8ec4900cc990bfb894387112ed
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fd, err := syscallcompat.Openat(dirfd, DirIVFilename, os.O_WRONLY|os.O_CREATE|os.O_EXCL, dirivPerms)
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if err != nil {
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tlog.Warn.Printf("WriteDirIV: Openat: %v", err)
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return err
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}
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// Wrap the fd in an os.File - we need the write retry logic.
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f := os.NewFile(uintptr(fd), DirIVFilename)
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_, err = f.Write(iv)
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if err != nil {
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f.Close()
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// It is normal to get ENOSPC here
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if !syscallcompat.IsENOSPC(err) {
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tlog.Warn.Printf("WriteDirIV: Write: %v", err)
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}
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// Delete incomplete gocryptfs.diriv file
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syscallcompat.Unlinkat(dirfd, DirIVFilename, 0)
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return err
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}
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err = f.Close()
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if err != nil {
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tlog.Warn.Printf("WriteDirIV: Close: %v", err)
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// Delete incomplete gocryptfs.diriv file
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syscallcompat.Unlinkat(dirfd, DirIVFilename, 0)
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return err
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}
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return nil
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}
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