330 lines
11 KiB
Go
330 lines
11 KiB
Go
package fusefrontend
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import (
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"os"
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"path/filepath"
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"strings"
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"sync"
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"sync/atomic"
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"syscall"
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"time"
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"github.com/rfjakob/gocryptfs/internal/configfile"
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"github.com/rfjakob/gocryptfs/internal/contentenc"
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"github.com/rfjakob/gocryptfs/internal/inomap"
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"github.com/rfjakob/gocryptfs/internal/nametransform"
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"github.com/rfjakob/gocryptfs/internal/serialize_reads"
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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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// RootNode is the root of the filesystem tree of Nodes.
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type RootNode struct {
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Node
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// args stores configuration arguments
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args Args
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// dirIVLock: Lock()ed if any "gocryptfs.diriv" file is modified
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// Readers must RLock() it to prevent them from seeing intermediate
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// states
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dirIVLock sync.RWMutex
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// Filename encryption helper
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nameTransform nametransform.NameTransformer
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// Content encryption helper
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contentEnc *contentenc.ContentEnc
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// This lock is used by openWriteOnlyFile() to block concurrent opens while
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// it relaxes the permissions on a file.
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openWriteOnlyLock sync.RWMutex
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// MitigatedCorruptions is used to report data corruption that is internally
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// mitigated by ignoring the corrupt item. For example, when OpenDir() finds
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// a corrupt filename, we still return the other valid filenames.
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// The corruption is logged to syslog to inform the user, and in addition,
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// the corrupt filename is logged to this channel via
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// reportMitigatedCorruption().
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// "gocryptfs -fsck" reads from the channel to also catch these transparently-
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// mitigated corruptions.
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MitigatedCorruptions chan string
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// IsIdle flag is set to zero each time fs.isFiltered() is called
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// (uint32 so that it can be reset with CompareAndSwapUint32).
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// When -idle was used when mounting, idleMonitor() sets it to 1
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// periodically.
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IsIdle uint32
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// dirCache caches directory fds
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dirCache dirCache
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// inoMap translates inode numbers from different devices to unique inode
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// numbers.
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inoMap inomap.TranslateStater
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}
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func NewRootNode(args Args, c *contentenc.ContentEnc, n nametransform.NameTransformer) *RootNode {
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if args.SerializeReads {
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serialize_reads.InitSerializer()
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}
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if len(args.Exclude) > 0 {
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tlog.Warn.Printf("Forward mode does not support -exclude")
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}
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rn := &RootNode{
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args: args,
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nameTransform: n,
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contentEnc: c,
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inoMap: inomap.New(),
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}
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// In `-sharedstorage` mode we always set the inode number to zero.
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// This makes go-fuse generate a new inode number for each lookup.
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if args.SharedStorage {
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rn.inoMap = &inomap.TranslateStatZero{}
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}
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return rn
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}
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// mangleOpenFlags is used by Create() and Open() to convert the open flags the user
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// wants to the flags we internally use to open the backing file.
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// The returned flags always contain O_NOFOLLOW.
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func (rn *RootNode) mangleOpenFlags(flags uint32) (newFlags int) {
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newFlags = int(flags)
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// Convert WRONLY to RDWR. We always need read access to do read-modify-write cycles.
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if (newFlags & syscall.O_ACCMODE) == syscall.O_WRONLY {
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newFlags = newFlags ^ os.O_WRONLY | os.O_RDWR
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}
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// We also cannot open the file in append mode, we need to seek back for RMW
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newFlags = newFlags &^ os.O_APPEND
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// O_DIRECT accesses must be aligned in both offset and length. Due to our
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// crypto header, alignment will be off, even if userspace makes aligned
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// accesses. Running xfstests generic/013 on ext4 used to trigger lots of
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// EINVAL errors due to missing alignment. Just fall back to buffered IO.
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newFlags = newFlags &^ syscallcompat.O_DIRECT
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// Create and Open are two separate FUSE operations, so O_CREAT should not
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// be part of the open flags.
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newFlags = newFlags &^ syscall.O_CREAT
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// We always want O_NOFOLLOW to be safe against symlink races
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newFlags |= syscall.O_NOFOLLOW
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return newFlags
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}
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// reportMitigatedCorruption is used to report a corruption that was transparently
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// mitigated and did not return an error to the user. Pass the name of the corrupt
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// item (filename for OpenDir(), xattr name for ListXAttr() etc).
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// See the MitigatedCorruptions channel for more info.
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func (rn *RootNode) reportMitigatedCorruption(item string) {
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if rn.MitigatedCorruptions == nil {
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return
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}
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select {
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case rn.MitigatedCorruptions <- item:
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case <-time.After(1 * time.Second):
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tlog.Warn.Printf("BUG: reportCorruptItem: timeout")
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//debug.PrintStack()
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return
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}
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}
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// isFiltered - check if plaintext "path" should be forbidden
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//
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// Prevents name clashes with internal files when file names are not encrypted
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func (rn *RootNode) isFiltered(path string) bool {
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atomic.StoreUint32(&rn.IsIdle, 0)
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if !rn.args.PlaintextNames {
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return false
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}
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// gocryptfs.conf in the root directory is forbidden
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if path == configfile.ConfDefaultName {
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tlog.Info.Printf("The name /%s is reserved when -plaintextnames is used\n",
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configfile.ConfDefaultName)
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return true
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}
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// Note: gocryptfs.diriv is NOT forbidden because diriv and plaintextnames
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// are exclusive
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return false
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}
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// decryptSymlinkTarget: "cData64" is base64-decoded and decrypted
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// like file contents (GCM).
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// The empty string decrypts to the empty string.
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//
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// This function does not do any I/O and is hence symlink-safe.
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func (rn *RootNode) decryptSymlinkTarget(cData64 string) (string, error) {
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if cData64 == "" {
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return "", nil
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}
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cData, err := rn.nameTransform.B64DecodeString(cData64)
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if err != nil {
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return "", err
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}
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data, err := rn.contentEnc.DecryptBlock([]byte(cData), 0, nil)
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if err != nil {
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return "", err
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}
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return string(data), nil
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}
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// Due to RMW, we always need read permissions on the backing file. This is a
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// problem if the file permissions do not allow reading (i.e. 0200 permissions).
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// This function works around that problem by chmod'ing the file, obtaining a fd,
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// and chmod'ing it back.
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func (rn *RootNode) openWriteOnlyFile(dirfd int, cName string, newFlags int) (rwFd int, err error) {
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woFd, err := syscallcompat.Openat(dirfd, cName, syscall.O_WRONLY|syscall.O_NOFOLLOW, 0)
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if err != nil {
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return
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}
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defer syscall.Close(woFd)
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var st syscall.Stat_t
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err = syscall.Fstat(woFd, &st)
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if err != nil {
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return
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}
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// The cast to uint32 fixes a build failure on Darwin, where st.Mode is uint16.
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perms := uint32(st.Mode)
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// Verify that we don't have read permissions
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if perms&0400 != 0 {
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tlog.Warn.Printf("openWriteOnlyFile: unexpected permissions %#o, returning EPERM", perms)
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err = syscall.EPERM
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return
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}
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// Upgrade the lock to block other Open()s and downgrade again on return
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rn.openWriteOnlyLock.RUnlock()
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rn.openWriteOnlyLock.Lock()
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defer func() {
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rn.openWriteOnlyLock.Unlock()
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rn.openWriteOnlyLock.RLock()
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}()
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// Relax permissions and revert on return
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err = syscall.Fchmod(woFd, perms|0400)
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if err != nil {
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tlog.Warn.Printf("openWriteOnlyFile: changing permissions failed: %v", err)
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return
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}
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defer func() {
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err2 := syscall.Fchmod(woFd, perms)
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if err2 != nil {
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tlog.Warn.Printf("openWriteOnlyFile: reverting permissions failed: %v", err2)
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}
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}()
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return syscallcompat.Openat(dirfd, cName, newFlags, 0)
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}
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// openBackingDir opens the parent ciphertext directory of plaintext path
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// "relPath". It returns the dirfd (opened with O_PATH) and the encrypted
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// basename.
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//
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// The caller should then use Openat(dirfd, cName, ...) and friends.
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// For convenience, if relPath is "", cName is going to be ".".
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//
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// openBackingDir is secure against symlink races by using Openat and
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// ReadDirIVAt.
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//
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// Retries on EINTR.
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func (rn *RootNode) openBackingDir(relPath string) (dirfd int, cName string, err error) {
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dirRelPath := nametransform.Dir(relPath)
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// With PlaintextNames, we don't need to read DirIVs. Easy.
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if rn.args.PlaintextNames {
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dirfd, err = syscallcompat.OpenDirNofollow(rn.args.Cipherdir, dirRelPath)
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if err != nil {
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return -1, "", err
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}
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// If relPath is empty, cName is ".".
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cName = filepath.Base(relPath)
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return dirfd, cName, nil
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}
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// Open cipherdir (following symlinks)
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dirfd, err = syscallcompat.Open(rn.args.Cipherdir, syscall.O_DIRECTORY|syscallcompat.O_PATH, 0)
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if err != nil {
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return -1, "", err
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}
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// If relPath is empty, cName is ".".
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if relPath == "" {
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return dirfd, ".", nil
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}
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// Walk the directory tree
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parts := strings.Split(relPath, "/")
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for i, name := range parts {
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iv, err := nametransform.ReadDirIVAt(dirfd)
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if err != nil {
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syscall.Close(dirfd)
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return -1, "", err
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}
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cName, err = rn.nameTransform.EncryptAndHashName(name, iv)
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if err != nil {
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syscall.Close(dirfd)
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return -1, "", err
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}
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// Last part? We are done.
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if i == len(parts)-1 {
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break
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}
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// Not the last part? Descend into next directory.
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dirfd2, err := syscallcompat.Openat(dirfd, cName, syscall.O_NOFOLLOW|syscall.O_DIRECTORY|syscallcompat.O_PATH, 0)
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syscall.Close(dirfd)
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if err != nil {
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return -1, "", err
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}
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dirfd = dirfd2
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}
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return dirfd, cName, nil
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}
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// encryptSymlinkTarget: "data" is encrypted like file contents (GCM)
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// and base64-encoded.
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// The empty string encrypts to the empty string.
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//
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// Symlink-safe because it does not do any I/O.
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func (rn *RootNode) encryptSymlinkTarget(data string) (cData64 string) {
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if data == "" {
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return ""
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}
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cData := rn.contentEnc.EncryptBlock([]byte(data), 0, nil)
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cData64 = rn.nameTransform.B64EncodeToString(cData)
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return cData64
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}
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// encryptXattrValue encrypts the xattr value "data".
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// The data is encrypted like a file content block, but without binding it to
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// a file location (block number and file id are set to zero).
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// Special case: an empty value is encrypted to an empty value.
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func (rn *RootNode) encryptXattrValue(data []byte) (cData []byte) {
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if len(data) == 0 {
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return []byte{}
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}
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return rn.contentEnc.EncryptBlock(data, 0, nil)
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}
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// decryptXattrValue decrypts the xattr value "cData".
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func (rn *RootNode) decryptXattrValue(cData []byte) (data []byte, err error) {
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if len(cData) == 0 {
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return []byte{}, nil
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}
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data, err1 := rn.contentEnc.DecryptBlock([]byte(cData), 0, nil)
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if err1 == nil {
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return data, nil
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}
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// This backward compatibility is needed to support old
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// file systems having xattr values base64-encoded.
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cData, err2 := rn.nameTransform.B64DecodeString(string(cData))
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if err2 != nil {
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// Looks like the value was not base64-encoded, but just corrupt.
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// Return the original decryption error: err1
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return nil, err1
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}
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return rn.contentEnc.DecryptBlock([]byte(cData), 0, nil)
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}
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// encryptXattrName transforms "user.foo" to "user.gocryptfs.a5sAd4XAa47f5as6dAf"
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func (rn *RootNode) encryptXattrName(attr string) (cAttr string) {
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// xattr names are encrypted like file names, but with a fixed IV.
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cAttr = xattrStorePrefix + rn.nameTransform.EncryptName(attr, xattrNameIV)
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return cAttr
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}
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func (rn *RootNode) decryptXattrName(cAttr string) (attr string, err error) {
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// Reject anything that does not start with "user.gocryptfs."
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if !strings.HasPrefix(cAttr, xattrStorePrefix) {
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return "", syscall.EINVAL
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}
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// Strip "user.gocryptfs." prefix
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cAttr = cAttr[len(xattrStorePrefix):]
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attr, err = rn.nameTransform.DecryptName(cAttr, xattrNameIV)
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if err != nil {
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return "", err
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}
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return attr, nil
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}
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