Return ENOENT when reading /proc/{pid}/task of an exited process

There will be a deadloop when we use getdents to read /proc/{pid}/task
of an exited process

Like this:

Process A is running
                         Process B: open /proc/{pid of A}/task
Process A exits
                         Process B: getdents /proc/{pid of A}/task

Then, process B will fall into deadloop, and return "." and ".."
in loops and never ends.

This patch returns ENOENT when use getdents to read /proc/{pid}/task
if the process is just exited.

Signed-off-by: chris.zn <chris.zn@antfin.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/pkg/sentry/fs/proc/task.go b/pkg/sentry/fs/proc/task.go
index b2e36aeee..22554bb88 100644
--- a/pkg/sentry/fs/proc/task.go
+++ b/pkg/sentry/fs/proc/task.go
@@ -20,6 +20,7 @@ import (
 	"io"
 	"sort"
 	"strconv"
+	"syscall"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/sentry/context"
@@ -162,6 +163,11 @@ func (f *subtasksFile) Readdir(ctx context.Context, file *fs.File, ser fs.Dentry
 	// subtask to emit.
 	offset := file.Offset()
 
+	tasks := f.t.ThreadGroup().MemberIDs(f.pidns)
+	if len(tasks) == 0 {
+		return offset, syscall.ENOENT
+	}
+
 	if offset == 0 {
 		// Serialize "." and "..".
 		root := fs.RootFromContext(ctx)
@@ -178,7 +184,6 @@ func (f *subtasksFile) Readdir(ctx context.Context, file *fs.File, ser fs.Dentry
 	}
 
 	// Serialize tasks.
-	tasks := f.t.ThreadGroup().MemberIDs(f.pidns)
 	taskInts := make([]int, 0, len(tasks))
 	for _, tid := range tasks {
 		taskInts = append(taskInts, int(tid))