hardcoresushi/libgocryptfs
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fusefronted: disallow writes running concurrently with reads

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As uncovered by xfstests generic/465, concurrent reads and writes
could lead to this,

  doRead 3015532: corrupt block #1039: stupidgcm: message authentication failed,

as the read could pick up a block that has not yet been completely written -
write() is not atomic!

Now writes take ContentLock exclusively, while reads take it shared,
meaning that multiple reads can run in parallel with each other, but
not with a write.

This also simplifies the file header locking.
This commit is contained in:
Jakob Unterwurzacher 2018-07-22 22:29:22 +02:00
parent c70df522d2
commit f316f1b2df
3 changed files with 45 additions and 65 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

86
internal/fusefrontend/file.go
View File

@ -145,39 +145,34 @@ func (f *File) createHeader() (fileID []byte, err error) {
//
// Called by Read() for normal reading,
// by Write() and Truncate() via doWrite() for Read-Modify-Write.
//
// doWrite() uses nolock=true because it makes sure the ID is in the cache and
// HeaderLock is locked before calling doRead.
func (f *File) doRead(dst []byte, off uint64, length uint64, nolock bool) ([]byte, fuse.Status) {
if !nolock {
// Make sure we have the file ID.
f.fileTableEntry.HeaderLock.RLock()
if f.fileTableEntry.ID == nil {
f.fileTableEntry.HeaderLock.RUnlock()
// Yes, somebody else may take the lock before we can. This will get
// the header read twice, but causes no harm otherwise.
f.fileTableEntry.HeaderLock.Lock()
tmpID, err := f.readFileID()
func (f *File) doRead(dst []byte, off uint64, length uint64) ([]byte, fuse.Status) {
// Get the file ID, either from the open file table, or from disk.
var fileID []byte
f.fileTableEntry.IDLock.Lock()
if f.fileTableEntry.ID != nil {
// Use the cached value in the file table
fileID = f.fileTableEntry.ID
} else {
// Not cached, we have to read it from disk.
var err error
fileID, err = f.readFileID()
if err != nil {
f.fileTableEntry.IDLock.Unlock()
if err == io.EOF {
f.fileTableEntry.HeaderLock.Unlock()
// Empty file
return nil, fuse.OK
}
if err != nil {
f.fileTableEntry.HeaderLock.Unlock()
tlog.Warn.Printf("doRead %d: corrupt header: %v", f.qIno.Ino, err)
return nil, fuse.EIO
}
f.fileTableEntry.ID = tmpID
// Downgrade the lock.
f.fileTableEntry.HeaderLock.Unlock()
// The file ID may change in here. This does no harm because we
// re-read it after the RLock().
f.fileTableEntry.HeaderLock.RLock()
}
// Save into the file table
f.fileTableEntry.ID = fileID
}
fileID := f.fileTableEntry.ID
f.fileTableEntry.IDLock.Unlock()
if fileID == nil {
log.Panicf("filedID=%v, nolock=%v", fileID, nolock)
log.Panicf("fileID=%v", fileID)
}
// Read the backing ciphertext in one go
blocks := f.contentEnc.ExplodePlainRange(off, length)
@ -189,10 +184,6 @@ func (f *File) doRead(dst []byte, off uint64, length uint64, nolock bool) ([]byt
ciphertext := f.fs.contentEnc.CReqPool.Get()
ciphertext = ciphertext[:int(alignedLength)]
n, err := f.fd.ReadAt(ciphertext, int64(alignedOffset))
// We don't care if the file ID changes after we have read the data. Drop the lock.
if !nolock {
f.fileTableEntry.HeaderLock.RUnlock()
}
if err != nil && err != io.EOF {
tlog.Warn.Printf("read: ReadAt: %s", err.Error())
return nil, fuse.ToStatus(err)
@ -251,11 +242,14 @@ func (f *File) Read(buf []byte, off int64) (resultData fuse.ReadResult, code fus
f.fdLock.RLock()
defer f.fdLock.RUnlock()
f.fileTableEntry.ContentLock.RLock()
defer f.fileTableEntry.ContentLock.RUnlock()
tlog.Debug.Printf("ino%d: FUSE Read: offset=%d length=%d", f.qIno.Ino, len(buf), off)
if f.fs.args.SerializeReads {
serialize_reads.Wait(off, len(buf))
}
out, status := f.doRead(buf[:0], uint64(off), uint64(len(buf)), false)
out, status := f.doRead(buf[:0], uint64(off), uint64(len(buf)))
if f.fs.args.SerializeReads {
serialize_reads.Done()
}
@ -277,31 +271,25 @@ func (f *File) Read(buf []byte, off int64) (resultData fuse.ReadResult, code fus
// Empty writes do nothing and are allowed.
func (f *File) doWrite(data []byte, off int64) (uint32, fuse.Status) {
fileWasEmpty := false
// If the file ID is not cached, read it from disk
if f.fileTableEntry.ID == nil {
// Block other readers while we mess with the file header. Other writers
// are blocked by ContentLock already.
f.fileTableEntry.HeaderLock.Lock()
tmpID, err := f.readFileID()
// Get the file ID, create a new one if it does not exist yet.
var fileID []byte
// The caller has exclusively locked ContentLock, which blocks all other
// readers and writers. No need to take IDLock.
if f.fileTableEntry.ID != nil {
fileID = f.fileTableEntry.ID
} else {
// If the file ID is not cached, read it from disk
var err error
fileID, err = f.readFileID()
// Write a new file header if the file is empty
if err == io.EOF {
tmpID, err = f.createHeader()
fileID, err = f.createHeader()
fileWasEmpty = true
}
if err != nil {
f.fileTableEntry.HeaderLock.Unlock()
return 0, fuse.ToStatus(err)
}
f.fileTableEntry.ID = tmpID
if fileWasEmpty {
// The file was empty and we wrote a new file header. Keep the lock
// as we might have to kill the file header again if the data write
// fails.
defer f.fileTableEntry.HeaderLock.Unlock()
} else {
// We won't touch the header again, drop the lock immediately.
f.fileTableEntry.HeaderLock.Unlock()
}
f.fileTableEntry.ID = fileID
}
// Handle payload data
dataBuf := bytes.NewBuffer(data)
@ -312,7 +300,7 @@ func (f *File) doWrite(data []byte, off int64) (uint32, fuse.Status) {
// Incomplete block -> Read-Modify-Write
if b.IsPartial() {
// Read
oldData, status := f.doRead(nil, b.BlockPlainOff(), f.contentEnc.PlainBS(), true)
oldData, status := f.doRead(nil, b.BlockPlainOff(), f.contentEnc.PlainBS())
if status != fuse.OK {
tlog.Warn.Printf("ino%d fh%d: RMW read failed: %s", f.qIno.Ino, f.intFd(), status.String())
return 0, status
@ -382,9 +370,7 @@ func (f *File) Write(data []byte, off int64) (uint32, fuse.Status) {
f.fdLock.RLock()
defer f.fdLock.RUnlock()
if f.released {
// The file descriptor has been closed concurrently, which also means
// the wlock has been freed. Exit here so we don't crash trying to access
// it.
// The file descriptor has been closed concurrently
tlog.Warn.Printf("ino%d fh%d: Write on released file", f.qIno.Ino, f.intFd())
return 0, fuse.EBADF
}

6
internal/fusefrontend/file_allocate_truncate.go
View File

@ -111,9 +111,7 @@ func (f *File) Truncate(newSize uint64) fuse.Status {
return fuse.ToStatus(err)
}
// Truncate to zero kills the file header
f.fileTableEntry.HeaderLock.Lock()
f.fileTableEntry.ID = nil
f.fileTableEntry.HeaderLock.Unlock()
return fuse.OK
}
// We need the old file size to determine if we are growing or shrinking
@ -144,7 +142,7 @@ func (f *File) Truncate(newSize uint64) fuse.Status {
var data []byte
if lastBlockLen > 0 {
var status fuse.Status
data, status = f.doRead(nil, plainOff, lastBlockLen, false)
data, status = f.doRead(nil, plainOff, lastBlockLen)
if status != fuse.OK {
tlog.Warn.Printf("Truncate: shrink doRead returned error: %v", err)
return status
@ -206,8 +204,6 @@ func (f *File) truncateGrowFile(oldPlainSz uint64, newPlainSz uint64) fuse.Statu
if newPlainSz%f.contentEnc.PlainBS() == 0 {
// The file was empty, so it did not have a header. Create one.
if oldPlainSz == 0 {
f.fileTableEntry.HeaderLock.Lock()
defer f.fileTableEntry.HeaderLock.Unlock()
id, err := f.createHeader()
if err != nil {
return fuse.ToStatus(err)

18
internal/openfiletable/open_file_table.go
View File

@ -57,18 +57,16 @@ type table struct {
// Entry is an entry in the open file table
type Entry struct {
// Reference count
// Reference count. Protected by the table lock.
refCount int
// ContentLock guards the file content from concurrent writes. Every writer
// ContentLock protects on-disk content from concurrent writes. Every writer
// must take this lock before modifying the file content.
ContentLock countingMutex
// HeaderLock guards the file ID (in this struct) and the file header (on
// disk). Take HeaderLock.RLock() to make sure the file ID does not change
// behind your back. If you modify the file ID, you must take
// HeaderLock.Lock().
HeaderLock sync.RWMutex
// ID is the file ID in the file header.
ID []byte
// IDLock must be taken before reading or writing the ID field in this struct,
// unless you have an exclusive lock on ContentLock.
IDLock sync.Mutex
}
// Register creates an open file table entry for "qi" (or incrementes the
@ -101,15 +99,15 @@ func Unregister(qi QIno) {
// countingMutex incrementes t.writeLockCount on each Lock() call.
type countingMutex struct {
sync.Mutex
sync.RWMutex
}
func (c *countingMutex) Lock() {
c.Mutex.Lock()
c.RWMutex.Lock()
atomic.AddUint64(&t.writeOpCount, 1)
}
// WriteOpCount returns the write lock counter value. This value is encremented
// WriteOpCount returns the write lock counter value. This value is incremented
// each time writeLock.Lock() on a file table entry is called.
func WriteOpCount() uint64 {
return atomic.LoadUint64(&t.writeOpCount)