From 52321c7e000382ce767ed920debb93f9aabf448b Mon Sep 17 00:00:00 2001
From: Andrei Vagin <avagin@google.com>
Date: Tue, 5 Mar 2024 07:44:21 -0800
Subject: [PATCH] kernel/pipe: trigger EPOLLERR on a write end if all readers
 has been closed

Fixes #10066

PiperOrigin-RevId: 612838688
---
 pkg/sentry/kernel/pipe/vfs.go |  3 +++
 test/syscalls/linux/epoll.cc  | 23 +++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/pkg/sentry/kernel/pipe/vfs.go b/pkg/sentry/kernel/pipe/vfs.go
index b4efd6ee1..0ada567ea 100644
--- a/pkg/sentry/kernel/pipe/vfs.go
+++ b/pkg/sentry/kernel/pipe/vfs.go
@@ -178,6 +178,9 @@ func (fd *VFSPipeFD) Release(context.Context) {
 	if fd.vfsfd.IsReadable() {
 		fd.pipe.rClose()
 		event |= waiter.WritableEvents
+		if !fd.pipe.HasReaders() {
+			event |= waiter.EventErr
+		}
 	}
 	if fd.vfsfd.IsWritable() {
 		fd.pipe.wClose()
diff --git a/test/syscalls/linux/epoll.cc b/test/syscalls/linux/epoll.cc
index 3b2168dab..9a4c0ed29 100644
--- a/test/syscalls/linux/epoll.cc
+++ b/test/syscalls/linux/epoll.cc
@@ -594,6 +594,29 @@ TEST(EpollTest, PipeReaderHupAfterWriterClosed) {
   EXPECT_EQ(result[0].data.u64, kMagicConstant);
 }
 
+TEST(EpollTest, PipeWriterErrAfterReaderClosed) {
+  auto epollfd = ASSERT_NO_ERRNO_AND_VALUE(NewEpollFD());
+  int pipefds[2];
+  ASSERT_THAT(pipe(pipefds), SyscallSucceeds());
+  FileDescriptor rfd(pipefds[0]);
+  FileDescriptor wfd(pipefds[1]);
+
+  ASSERT_NO_ERRNO(
+      RegisterEpollFD(epollfd.get(), wfd.get(), EPOLLERR, kMagicConstant));
+  struct epoll_event result[kFDsPerEpoll];
+  // Initially, wfd should not generate any events of interest.
+  ASSERT_THAT(epoll_wait(epollfd.get(), result, kFDsPerEpoll, 0),
+              SyscallSucceedsWithValue(0));
+  // Close the read end of the pipe.
+  rfd.reset();
+  // wfd should now generate EPOLLERR, which EPOLL_CTL_ADD unconditionally adds
+  // to the set of events of interest.
+  ASSERT_THAT(epoll_wait(epollfd.get(), result, kFDsPerEpoll, 0),
+              SyscallSucceedsWithValue(1));
+  EXPECT_EQ(result[0].events, EPOLLERR);
+  EXPECT_EQ(result[0].data.u64, kMagicConstant);
+}
+
 TEST(EpollTest, DoubleLayerEpoll) {
   int pipefds[2];
   ASSERT_THAT(pipe2(pipefds, O_NONBLOCK), SyscallSucceeds());