Fix vfs2 proc/self/fd dirent iteration.

Make proc/self/fd iteration work properly. Also, the comment on
kernfs.Inode.IterDirents did not accurately reflect how parameters should be
used/were used in kernfs.Inode impls other than fdDir.

Updates #2923.

PiperOrigin-RevId: 317370325

2 files changed, 5 insertions, 6 deletions

diff --git a/pkg/sentry/fsimpl/kernfs/kernfs.go b/pkg/sentry/fsimpl/kernfs/kernfs.go
index bbee8ccda..07a9dc830 100644
--- a/pkg/sentry/fsimpl/kernfs/kernfs.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs.go
@@ -425,10 +425,10 @@ type inodeDynamicLookup interface {
 	// IterDirents is used to iterate over dynamically created entries. It invokes
 	// cb on each entry in the directory represented by the FileDescription.
 	// 'offset' is the offset for the entire IterDirents call, which may include
-	// results from the caller. 'relOffset' is the offset inside the entries
-	// returned by this IterDirents invocation. In other words,
-	// 'offset+relOffset+1' is the value that should be set in vfs.Dirent.NextOff,
-	// while 'relOffset' is the place where iteration should start from.
+	// results from the caller (e.g. "." and ".."). 'relOffset' is the offset
+	// inside the entries returned by this IterDirents invocation. In other words,
+	// 'offset' should be used to calculate each vfs.Dirent.NextOff as well as
+	// the return value, while 'relOffset' is the place to start iteration.
 	IterDirents(ctx context.Context, callback vfs.IterDirentsCallback, offset, relOffset int64) (newOffset int64, err error)
 }
 
diff --git a/pkg/sentry/fsimpl/proc/task_fds.go b/pkg/sentry/fsimpl/proc/task_fds.go
index 7debdb07a..fea29e5f0 100644
--- a/pkg/sentry/fsimpl/proc/task_fds.go
+++ b/pkg/sentry/fsimpl/proc/task_fds.go
@@ -64,7 +64,7 @@ type fdDir struct {
 }
 
 // IterDirents implements kernfs.inodeDynamicLookup.
-func (i *fdDir) IterDirents(ctx context.Context, cb vfs.IterDirentsCallback, absOffset, relOffset int64) (int64, error) {
+func (i *fdDir) IterDirents(ctx context.Context, cb vfs.IterDirentsCallback, offset, relOffset int64) (int64, error) {
 	var fds []int32
 	i.task.WithMuLocked(func(t *kernel.Task) {
 		if fdTable := t.FDTable(); fdTable != nil {
@@ -72,7 +72,6 @@ func (i *fdDir) IterDirents(ctx context.Context, cb vfs.IterDirentsCallback, abs
 		}
 	})
 
-	offset := absOffset + relOffset
 	typ := uint8(linux.DT_REG)
 	if i.produceSymlink {
 		typ = linux.DT_LNK