3 files changed, 61 insertions, 2 deletions
diff --git a/pkg/sentry/fs/fsutil/host_file_mapper.go b/pkg/sentry/fs/fsutil/host_file_mapper.go
index e239f12a5..b06a71cc2 100644
--- a/pkg/sentry/fs/fsutil/host_file_mapper.go
+++ b/pkg/sentry/fs/fsutil/host_file_mapper.go
@@ -209,3 +209,29 @@ func (f *HostFileMapper) unmapAndRemoveLocked(chunkStart uint64, m mapping) {
 	}
 	delete(f.mappings, chunkStart)
 }
+
+// RegenerateMappings must be called when the file description mapped by f
+// changes, to replace existing mappings of the previous file description.
+func (f *HostFileMapper) RegenerateMappings(fd int) error {
+	f.mapsMu.Lock()
+	defer f.mapsMu.Unlock()
+
+	for chunkStart, m := range f.mappings {
+		prot := syscall.PROT_READ
+		if m.writable {
+			prot |= syscall.PROT_WRITE
+		}
+		_, _, errno := syscall.Syscall6(
+			syscall.SYS_MMAP,
+			m.addr,
+			chunkSize,
+			uintptr(prot),
+			syscall.MAP_SHARED|syscall.MAP_FIXED,
+			uintptr(fd),
+			uintptr(chunkStart))
+		if errno != 0 {
+			return errno
+		}
+	}
+	return nil
+}
diff --git a/pkg/sentry/fs/fsutil/host_mappable.go b/pkg/sentry/fs/fsutil/host_mappable.go
index 693625ddc..30475f340 100644
--- a/pkg/sentry/fs/fsutil/host_mappable.go
+++ b/pkg/sentry/fs/fsutil/host_mappable.go
@@ -100,13 +100,30 @@ func (h *HostMappable) Translate(ctx context.Context, required, optional memmap.
 }
 
 // InvalidateUnsavable implements memmap.Mappable.InvalidateUnsavable.
-func (h *HostMappable) InvalidateUnsavable(ctx context.Context) error {
+func (h *HostMappable) InvalidateUnsavable(_ context.Context) error {
 	h.mu.Lock()
 	h.mappings.InvalidateAll(memmap.InvalidateOpts{})
 	h.mu.Unlock()
 	return nil
 }
 
+// NotifyChangeFD must be called after the file description represented by
+// CachedFileObject.FD() changes.
+func (h *HostMappable) NotifyChangeFD() error {
+	// Update existing sentry mappings to refer to the new file description.
+	if err := h.hostFileMapper.RegenerateMappings(h.backingFile.FD()); err != nil {
+		return err
+	}
+
+	// Shoot down existing application mappings of the old file description;
+	// they will be remapped with the new file description on demand.
+	h.mu.Lock()
+	defer h.mu.Unlock()
+
+	h.mappings.InvalidateAll(memmap.InvalidateOpts{})
+	return nil
+}
+
 // MapInternal implements platform.File.MapInternal.
 func (h *HostMappable) MapInternal(fr platform.FileRange, at usermem.AccessType) (safemem.BlockSeq, error) {
 	return h.hostFileMapper.MapInternal(fr, h.backingFile.FD(), at.Write)
diff --git a/pkg/sentry/fs/fsutil/inode_cached.go b/pkg/sentry/fs/fsutil/inode_cached.go
index dd80757dc..798920d18 100644
--- a/pkg/sentry/fs/fsutil/inode_cached.go
+++ b/pkg/sentry/fs/fsutil/inode_cached.go
@@ -959,6 +959,23 @@ func (c *CachingInodeOperations) InvalidateUnsavable(ctx context.Context) error
 	return nil
 }
 
+// NotifyChangeFD must be called after the file description represented by
+// CachedFileObject.FD() changes.
+func (c *CachingInodeOperations) NotifyChangeFD() error {
+	// Update existing sentry mappings to refer to the new file description.
+	if err := c.hostFileMapper.RegenerateMappings(c.backingFile.FD()); err != nil {
+		return err
+	}
+
+	// Shoot down existing application mappings of the old file description;
+	// they will be remapped with the new file description on demand.
+	c.mapsMu.Lock()
+	defer c.mapsMu.Unlock()
+
+	c.mappings.InvalidateAll(memmap.InvalidateOpts{})
+	return nil
+}
+
 // Evict implements pgalloc.EvictableMemoryUser.Evict.
 func (c *CachingInodeOperations) Evict(ctx context.Context, er pgalloc.EvictableRange) {
 	c.mapsMu.Lock()
@@ -1027,7 +1044,6 @@ func (c *CachingInodeOperations) DecRef(fr platform.FileRange) {
 	}
 	c.refs.MergeAdjacent(fr)
 	c.dataMu.Unlock()
-
 }
 
 // MapInternal implements platform.File.MapInternal. This is used when we