From 4cd4759238655e35c8dc63723f4e55014b5ea9ea Mon Sep 17 00:00:00 2001
From: Jamie Liu <jamieliu@google.com>
Date: Wed, 29 Jul 2020 14:56:14 -0700
Subject: Force registration for EPOLLHUP, not EPOLLRDHUP, in vfs2's epoll.

Compare Linux's fs/eventpoll.c:do_epoll_ctl(). I don't know where EPOLLRDHUP
came from.

PiperOrigin-RevId: 323874419
---
 pkg/sentry/vfs/epoll.go      |  4 ++--
 test/syscalls/linux/epoll.cc | 22 ++++++++++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/pkg/sentry/vfs/epoll.go b/pkg/sentry/vfs/epoll.go
index 599c3131c..5b009b928 100644
--- a/pkg/sentry/vfs/epoll.go
+++ b/pkg/sentry/vfs/epoll.go
@@ -186,7 +186,7 @@ func (ep *EpollInstance) AddInterest(file *FileDescription, num int32, event lin
 	}
 
 	// Register interest in file.
-	mask := event.Events | linux.EPOLLERR | linux.EPOLLRDHUP
+	mask := event.Events | linux.EPOLLERR | linux.EPOLLHUP
 	epi := &epollInterest{
 		epoll:    ep,
 		key:      key,
@@ -257,7 +257,7 @@ func (ep *EpollInstance) ModifyInterest(file *FileDescription, num int32, event
 	}
 
 	// Update epi for the next call to ep.ReadEvents().
-	mask := event.Events | linux.EPOLLERR | linux.EPOLLRDHUP
+	mask := event.Events | linux.EPOLLERR | linux.EPOLLHUP
 	ep.mu.Lock()
 	epi.mask = mask
 	epi.userData = event.Data
diff --git a/test/syscalls/linux/epoll.cc b/test/syscalls/linux/epoll.cc
index f57d38dc7..2101e5c9f 100644
--- a/test/syscalls/linux/epoll.cc
+++ b/test/syscalls/linux/epoll.cc
@@ -422,6 +422,28 @@ TEST(EpollTest, CloseFile) {
               SyscallSucceedsWithValue(0));
 }
 
+TEST(EpollTest, PipeReaderHupAfterWriterClosed) {
+  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(), rfd.get(), 0, kMagicConstant));
+  struct epoll_event result[kFDsPerEpoll];
+  // Initially, rfd should not generate any events of interest.
+  ASSERT_THAT(epoll_wait(epollfd.get(), result, kFDsPerEpoll, 0),
+              SyscallSucceedsWithValue(0));
+  // Close the write end of the pipe.
+  wfd.reset();
+  // rfd should now generate EPOLLHUP, 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, EPOLLHUP);
+  EXPECT_EQ(result[0].data.u64, kMagicConstant);
+}
+
 }  // namespace
 
 }  // namespace testing
-- 
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