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-rw-r--r--internal/fusefrontend/file.go16
-rw-r--r--internal/fusefrontend/file_lock.go29
2 files changed, 45 insertions, 0 deletions
diff --git a/internal/fusefrontend/file.go b/internal/fusefrontend/file.go
index 0e25de3..5be0872 100644
--- a/internal/fusefrontend/file.go
+++ b/internal/fusefrontend/file.go
@@ -14,6 +14,8 @@ import (
"sync"
"syscall"
+ "golang.org/x/sys/unix"
+
"github.com/hanwen/go-fuse/v2/fs"
"github.com/hanwen/go-fuse/v2/fuse"
@@ -91,6 +93,13 @@ func (f *File) readFileID() ([]byte, error) {
// and not only the header. A header-only file will be considered empty.
// This makes File ID poisoning more difficult.
readLen := contentenc.HeaderLen + 1
+ if f.rootNode.args.SharedStorage {
+ // With -sharedstorage, we consider a header-only file as valid, because
+ // another gocryptfs process may have either:
+ // 1) just created the header, and not written further data yet.
+ // 2) truncated the file down to just the header.
+ readLen = contentenc.HeaderLen
+ }
buf := make([]byte, readLen)
n, err := f.fd.ReadAt(buf, 0)
if err != nil {
@@ -267,18 +276,25 @@ func (f *File) doWrite(data []byte, off int64) (uint32, syscall.Errno) {
//
// If the file ID is not cached, read it from disk
if f.fileTableEntry.ID == nil {
+ if err := f.LockSharedStorage(unix.F_WRLCK, 0, contentenc.HeaderLen); err != nil {
+ return 0, fs.ToErrno(err)
+ }
var err error
fileID, err := f.readFileID()
// Write a new file header if the file is empty
if err == io.EOF {
fileID, err = f.createHeader()
fileWasEmpty = true
+ // Having the unlock three times is ugly. But every other way I tried is even uglier.
+ f.LockSharedStorage(unix.F_UNLCK, 0, contentenc.HeaderLen)
} else if err != nil {
// Other errors mean readFileID() found a corrupt header
tlog.Warn.Printf("doWrite %d: corrupt header: %v", f.qIno.Ino, err)
+ f.LockSharedStorage(unix.F_UNLCK, 0, contentenc.HeaderLen)
return 0, syscall.EIO
}
if err != nil {
+ f.LockSharedStorage(unix.F_UNLCK, 0, contentenc.HeaderLen)
return 0, fs.ToErrno(err)
}
f.fileTableEntry.ID = fileID
diff --git a/internal/fusefrontend/file_lock.go b/internal/fusefrontend/file_lock.go
new file mode 100644
index 0000000..6f92cfe
--- /dev/null
+++ b/internal/fusefrontend/file_lock.go
@@ -0,0 +1,29 @@
+package fusefrontend
+
+import (
+ "golang.org/x/sys/unix"
+
+ "github.com/rfjakob/gocryptfs/v2/internal/syscallcompat"
+)
+
+// SharedStorageLock conveniently wraps F_OFD_SETLKW
+// See https://man7.org/linux/man-pages/man2/fcntl.2.html -> "Open file description locks (non-POSIX)"
+//
+// lkType is one of:
+// * unix.F_RDLCK (shared read lock)
+// * unix.F_WRLCK (exclusive write lock)
+// * unix.F_UNLCK (unlock)
+//
+// This function is a no-op if args.SharedStorage == false.
+func (f *File) LockSharedStorage(lkType int16, lkStart int64, lkLen int64) error {
+ if !f.rootNode.args.SharedStorage {
+ return nil
+ }
+ lk := unix.Flock_t{
+ Type: lkType,
+ Whence: unix.SEEK_SET,
+ Start: lkStart,
+ Len: lkLen,
+ }
+ return unix.FcntlFlock(uintptr(f.intFd()), syscallcompat.F_OFD_SETLKW, &lk)
+}