Fix EOF handling for splice.

Also, add corresponding EOF tests for splice/sendfile.

Discovered by syzkaller.

PiperOrigin-RevId: 328975990

pkg/sentry/syscalls/linux/vfs2/splice.go

@@ -141,9 +141,14 @@ func Splice(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Syscal
 				inOffset += n
 			}
 		default:
-			panic("not possible")
+			panic("at least one end of splice must be a pipe")
 		}
 
+		if n == 0 && err == io.EOF {
+			// We reached the end of the file. Eat the error and exit the loop.
+			err = nil
+			break
+		}
 		if n != 0 || err != syserror.ErrWouldBlock || nonBlock {
 			break
 		}

test/syscalls/linux/sendfile.cc

@@ -533,6 +533,22 @@ TEST(SendFileTest, SendPipeWouldBlock) {
               SyscallFailsWithErrno(EWOULDBLOCK));
 }
 
+TEST(SendFileTest, SendPipeEOF) {
+  // Create and open an empty input file.
+  const TempPath in_file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
+  const FileDescriptor inf =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(in_file.path(), O_RDONLY));
+
+  // Setup the output named pipe.
+  int fds[2];
+  ASSERT_THAT(pipe2(fds, O_NONBLOCK), SyscallSucceeds());
+  const FileDescriptor rfd(fds[0]);
+  const FileDescriptor wfd(fds[1]);
+
+  EXPECT_THAT(sendfile(wfd.get(), inf.get(), nullptr, 123),
+              SyscallSucceedsWithValue(0));
+}
+
 TEST(SendFileTest, SendPipeBlocks) {
   // Create temp file.
   constexpr char kData[] =

test/syscalls/linux/splice.cc

@@ -298,6 +298,23 @@ TEST(SpliceTest, ToPipe) {
   EXPECT_EQ(memcmp(rbuf.data(), buf.data(), buf.size()), 0);
 }
 
+TEST(SpliceTest, ToPipeEOF) {
+  // Create and open an empty input file.
+  const TempPath in_file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
+  const FileDescriptor in_fd =
+      ASSERT_NO_ERRNO_AND_VALUE(Open(in_file.path(), O_RDONLY));
+
+  // Create a new pipe.
+  int fds[2];
+  ASSERT_THAT(pipe(fds), SyscallSucceeds());
+  const FileDescriptor rfd(fds[0]);
+  const FileDescriptor wfd(fds[1]);
+
+  // Splice from the empty file to the pipe.
+  EXPECT_THAT(splice(in_fd.get(), nullptr, wfd.get(), nullptr, 123, 0),
+              SyscallSucceedsWithValue(0));
+}
+
 TEST(SpliceTest, ToPipeOffset) {
   // Open the input file.
   const TempPath in_file = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());