net/http: close request body after recovering from a handler panic

When recovering from a panic in a HTTP handler, close the request body
before closing the *conn, ensuring that the *conn's bufio.Reader is safe
to recycle.

Fixes #46866.

Change-Id: I3fe304592e3b423a0970727d68bc1229c3752939
Reviewed-on: https://go-review.googlesource.com/c/go/+/329922
Trust: Damien Neil <dneil@google.com>
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/server.go

@@ -1794,6 +1794,7 @@ func isCommonNetReadError(err error) bool {
 func (c *conn) serve(ctx context.Context) {
 	c.remoteAddr = c.rwc.RemoteAddr().String()
 	ctx = context.WithValue(ctx, LocalAddrContextKey, c.rwc.LocalAddr())
+	var inFlightResponse *response
 	defer func() {
 		if err := recover(); err != nil && err != ErrAbortHandler {
 			const size = 64 << 10
@@ -1801,7 +1802,14 @@ func (c *conn) serve(ctx context.Context) {
 			buf = buf[:runtime.Stack(buf, false)]
 			c.server.logf("http: panic serving %v: %v\n%s", c.remoteAddr, err, buf)
 		}
+		if inFlightResponse != nil {
+			inFlightResponse.cancelCtx()
+		}
 		if !c.hijacked() {
+			if inFlightResponse != nil {
+				inFlightResponse.conn.r.abortPendingRead()
+				inFlightResponse.reqBody.Close()
+			}
 			c.close()
 			c.setState(c.rwc, StateClosed, runHooks)
 		}
@@ -1926,7 +1934,9 @@ func (c *conn) serve(ctx context.Context) {
 		// in parallel even if their responses need to be serialized.
 		// But we're not going to implement HTTP pipelining because it
 		// was never deployed in the wild and the answer is HTTP/2.
+		inFlightResponse = w
 		serverHandler{c.server}.ServeHTTP(w, w.req)
+		inFlightResponse = nil
 		w.cancelCtx()
 		if c.hijacked() {
 			return

src/net/http/transport_test.go

@@ -6512,3 +6512,32 @@ func TestCancelRequestWhenSharingConnection(t *testing.T) {
 	close(r2c)
 	wg.Wait()
 }
+
+func TestHandlerAbortRacesBodyRead(t *testing.T) {
+	setParallel(t)
+	defer afterTest(t)
+
+	ts := httptest.NewServer(HandlerFunc(func(rw ResponseWriter, req *Request) {
+		go io.Copy(io.Discard, req.Body)
+		panic(ErrAbortHandler)
+	}))
+	defer ts.Close()
+
+	var wg sync.WaitGroup
+	for i := 0; i < 2; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for j := 0; j < 10; j++ {
+				const reqLen = 6 * 1024 * 1024
+				req, _ := NewRequest("POST", ts.URL, &io.LimitedReader{R: neverEnding('x'), N: reqLen})
+				req.ContentLength = reqLen
+				resp, _ := ts.Client().Transport.RoundTrip(req)
+				if resp != nil {
+					resp.Body.Close()
+				}
+			}
+		}()
+	}
+	wg.Wait()
+}