Invalidate COW mappings when file is truncated

This changed required making fsutil.HostMappable use
a backing file to ensure the correct FD would be used
for read/write operations.

RELNOTES: relnotes is needed for the parent CL.
PiperOrigin-RevId: 231836164
Change-Id: I8ae9639715529874ea7d80a65e2c711a5b4ce254

3 files changed, 13 insertions, 13 deletions

diff --git a/pkg/sentry/fs/gofer/file.go b/pkg/sentry/fs/gofer/file.go
index 2181ddc68..2bb25daf1 100644
--- a/pkg/sentry/fs/gofer/file.go
+++ b/pkg/sentry/fs/gofer/file.go
@@ -215,6 +215,9 @@ func (f *fileOperations) Write(ctx context.Context, file *fs.File, src usermem.I
 		}
 		return n, err
 	}
+	if f.inodeOperations.fileState.hostMappable != nil {
+		return f.inodeOperations.fileState.hostMappable.Write(ctx, src, offset)
+	}
 	return src.CopyInTo(ctx, f.handles.readWriterAt(ctx, offset))
 }
 
diff --git a/pkg/sentry/fs/gofer/inode.go b/pkg/sentry/fs/gofer/inode.go
index 043705c58..1dc0ca0db 100644
--- a/pkg/sentry/fs/gofer/inode.go
+++ b/pkg/sentry/fs/gofer/inode.go
@@ -170,9 +170,6 @@ func (i *inodeFileState) setHandlesForCachedIO(flags fs.FileFlags, h *handles) {
 			i.writebackRW = true
 		}
 	}
-	if i.hostMappable != nil {
-		i.hostMappable.UpdateFD(i.fdLocked())
-	}
 }
 
 // getCachedHandles returns any cached handles which would accelerate
@@ -520,6 +517,9 @@ func (i *inodeOperations) Truncate(ctx context.Context, inode *fs.Inode, length
 	if i.session().cachePolicy.useCachingInodeOps(inode) {
 		return i.cachingInodeOps.Truncate(ctx, inode, length)
 	}
+	if i.session().cachePolicy == cacheRemoteRevalidating {
+		return i.fileState.hostMappable.Truncate(ctx, length)
+	}
 
 	return i.fileState.file.setAttr(ctx, p9.SetAttrMask{Size: true}, p9.SetAttr{Size: uint64(length)})
 }
diff --git a/pkg/sentry/fs/gofer/session.go b/pkg/sentry/fs/gofer/session.go
index b5b1c8202..d626b86f5 100644
--- a/pkg/sentry/fs/gofer/session.go
+++ b/pkg/sentry/fs/gofer/session.go
@@ -197,17 +197,14 @@ func newInodeOperations(ctx context.Context, s *session, file contextFile, qid p
 		}
 	}
 
-	var hm *fsutil.HostMappable
-	if s.cachePolicy == cacheRemoteRevalidating && fs.IsFile(sattr) {
-		hm = fsutil.NewHostMappable()
-	}
-
 	fileState := &inodeFileState{
-		s:            s,
-		file:         file,
-		sattr:        sattr,
-		key:          deviceKey,
-		hostMappable: hm,
+		s:     s,
+		file:  file,
+		sattr: sattr,
+		key:   deviceKey,
+	}
+	if s.cachePolicy == cacheRemoteRevalidating && fs.IsFile(sattr) {
+		fileState.hostMappable = fsutil.NewHostMappable(fileState)
 	}
 
 	uattr := unstable(ctx, valid, attr, s.mounter, s.client)