taildrop: fix theoretical race condition in fileDeleter.Init (#9876)

It is possible that upon a cold-start, we enqueue a partial file
for deletion that is resumed shortly after startup.

If the file transfer happens to last longer than deleteDelay,
we will delete the partial file, which is unfortunate.
The client spent a long time uploading a file,
only for it to be accidentally deleted.
It's a very rare race, but also a frustrating one
if it happens to manifest.

Fix the code to only delete partial files that
do not have an active puts against it.

We also fix a minor bug in ResumeReader
where we read b[:blockSize] instead of b[:cs.Size].
The former is the fixed size of 64KiB,
while the latter is usually 64KiB,
but may be less for the last block.

Updates tailscale/corp#14772

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

taildrop/delete.go

@@ -27,8 +27,8 @@ const deleteDelay = time.Hour
 type fileDeleter struct {
 	logf  logger.Logf
 	clock tstime.DefaultClock
-	event func(string) // called for certain events; for testing only
 	dir   string
+	event func(string) // called for certain events; for testing only
 
 	mu     sync.Mutex
 	queue  list.List
@@ -46,11 +46,11 @@ type deleteFile struct {
 	inserted time.Time
 }
 
-func (d *fileDeleter) Init(logf logger.Logf, clock tstime.DefaultClock, event func(string), dir string) {
-	d.logf = logf
-	d.clock = clock
-	d.dir = dir
-	d.event = event
+func (d *fileDeleter) Init(m *Manager, eventHook func(string)) {
+	d.logf = m.opts.Logf
+	d.clock = m.opts.Clock
+	d.dir = m.opts.Dir
+	d.event = eventHook
 
 	// From a cold-start, load the list of partial and deleted files.
 	d.byName = make(map[string]*list.Element)
@@ -59,19 +59,30 @@ func (d *fileDeleter) Init(logf logger.Logf, clock tstime.DefaultClock, event fu
 	d.group.Go(func() {
 		d.event("start init")
 		defer d.event("end init")
-		rangeDir(dir, func(de fs.DirEntry) bool {
+		rangeDir(d.dir, func(de fs.DirEntry) bool {
 			switch {
 			case d.shutdownCtx.Err() != nil:
 				return false // terminate early
 			case !de.Type().IsRegular():
 				return true
-			case strings.Contains(de.Name(), partialSuffix):
-				d.Insert(de.Name())
-			case strings.Contains(de.Name(), deletedSuffix):
+			case strings.HasSuffix(de.Name(), partialSuffix):
+				// Only enqueue the file for deletion if there is no active put.
+				nameID := strings.TrimSuffix(de.Name(), partialSuffix)
+				if i := strings.LastIndexByte(nameID, '.'); i > 0 {
+					key := incomingFileKey{ClientID(nameID[i+len("."):]), nameID[:i]}
+					m.incomingFiles.LoadFunc(key, func(_ *incomingFile, loaded bool) {
+						if !loaded {
+							d.Insert(de.Name())
+						}
+					})
+				} else {
+					d.Insert(de.Name())
+				}
+			case strings.HasSuffix(de.Name(), deletedSuffix):
 				// Best-effort immediate deletion of deleted files.
 				name := strings.TrimSuffix(de.Name(), deletedSuffix)
-				if os.Remove(filepath.Join(dir, name)) == nil {
-					if os.Remove(filepath.Join(dir, de.Name())) == nil {
+				if os.Remove(filepath.Join(d.dir, name)) == nil {
+					if os.Remove(filepath.Join(d.dir, de.Name())) == nil {
 						break
 					}
 				}