Fix data race on inotify.Watch.mask.

PiperOrigin-RevId: 203180463
Change-Id: Ief50988c1c028f81ec07a26e704d893e86985bf0

pkg/sentry/fs/inotify.go

@@ -16,6 +16,7 @@ package fs
 
 import (
 	"sync"
+	"sync/atomic"
 
 	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
 	"gvisor.googlesource.com/gvisor/pkg/ilist"
@@ -279,13 +280,13 @@ func (i *Inotify) AddWatch(target *Dirent, mask uint32) int32 {
 		// same inode. Obtain an extra reference if necessary.
 		existing.Pin(target)
 
+		newmask := mask
 		if mergeMask := mask&linux.IN_MASK_ADD != 0; mergeMask {
 			// "Add (OR) events to watch mask for this pathname if it already
 			// exists (instead of replacing mask)." -- inotify(7)
-			existing.mask |= mask
-		} else {
-			existing.mask = mask
+			newmask |= atomic.LoadUint32(&existing.mask)
 		}
+		atomic.StoreUint32(&existing.mask, newmask)
 		return existing.wd
 	}
 

pkg/sentry/fs/inotify_watch.go

@@ -16,6 +16,7 @@ package fs
 
 import (
 	"sync"
+	"sync/atomic"
 
 	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
 )
@@ -33,9 +34,6 @@ type Watch struct {
 	// Descriptor for this watch. This is unique across an inotify instance.
 	wd int32
 
-	// Events being monitored via this watch.
-	mask uint32
-
 	// The inode being watched. Note that we don't directly hold a reference on
 	// this inode. Instead we hold a reference on the dirent(s) containing the
 	// inode, which we record in pins.
@@ -48,6 +46,10 @@ type Watch struct {
 	// mu protects the fields below.
 	mu sync.Mutex `state:"nosave"`
 
+	// Events being monitored via this watch. Must be accessed atomically,
+	// writes are protected by mu.
+	mask uint32
+
 	// pins is the set of dirents this watch is currently pinning in memory by
 	// holding a reference to them. See Pin()/Unpin().
 	pins map[*Dirent]bool
@@ -62,7 +64,7 @@ func (w *Watch) ID() uint64 {
 // should continue to be be notified of events after the target has been
 // unlinked.
 func (w *Watch) NotifyParentAfterUnlink() bool {
-	return w.mask&linux.IN_EXCL_UNLINK == 0
+	return atomic.LoadUint32(&w.mask)&linux.IN_EXCL_UNLINK == 0
 }
 
 // isRenameEvent returns true if eventMask describes a rename event.
@@ -73,7 +75,7 @@ func isRenameEvent(eventMask uint32) bool {
 // Notify queues a new event on this watch.
 func (w *Watch) Notify(name string, events uint32, cookie uint32) {
 	unmaskableBits := ^uint32(0) &^ linux.IN_ALL_EVENTS
-	effectiveMask := unmaskableBits | w.mask
+	effectiveMask := unmaskableBits | atomic.LoadUint32(&w.mask)
 	matchedEvents := effectiveMask & events
 
 	if matchedEvents == 0 {