From f8b2315b75ad8a9c8b386502504525e1816982cd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dan=20=C4=8Cerm=C3=A1k?= <dcermak@suse.com>
Date: Wed, 12 Feb 2025 15:33:28 +0100
Subject: [PATCH 4/4] http2: close connections when receiving too many headers
 (#1)

Maintaining HPACK state requires that we parse and process
all HEADERS and CONTINUATION frames on a connection.
When a request's headers exceed MaxHeaderBytes, we don't
allocate memory to store the excess headers but we do
parse them. This permits an attacker to cause an HTTP/2
endpoint to read arbitrary amounts of data, all associated
with a request which is going to be rejected.

Set a limit on the amount of excess header frames we
will process before closing a connection.

Thanks to Bartek Nowotarski for reporting this issue.

Fixes CVE-2023-45288
Fixes bsc#1236531

This is a backport of
https://go.googlesource.com/net/+/ba872109ef2dc8f1da778651bd1fd3792d0e4587%5E%21/#F0
---
 vendor/golang.org/x/net/http2/frame.go | 31 ++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/vendor/golang.org/x/net/http2/frame.go b/vendor/golang.org/x/net/http2/frame.go
index e2b298d85..a5a94411d 100644
--- a/vendor/golang.org/x/net/http2/frame.go
+++ b/vendor/golang.org/x/net/http2/frame.go
@@ -1564,6 +1564,7 @@ func (fr *Framer) readMetaFrame(hf *HeadersFrame) (*MetaHeadersFrame, error) {
 		if size > remainSize {
 			hdec.SetEmitEnabled(false)
 			mh.Truncated = true
+			remainSize = 0
 			return
 		}
 		remainSize -= size
@@ -1576,6 +1577,36 @@ func (fr *Framer) readMetaFrame(hf *HeadersFrame) (*MetaHeadersFrame, error) {
 	var hc headersOrContinuation = hf
 	for {
 		frag := hc.HeaderBlockFragment()
+
+		// Avoid parsing large amounts of headers that we will then discard.
+		// If the sender exceeds the max header list size by too much,
+		// skip parsing the fragment and close the connection.
+		//
+		// "Too much" is either any CONTINUATION frame after we've already
+		// exceeded the max header list size (in which case remainSize is 0),
+		// or a frame whose encoded size is more than twice the remaining
+		// header list bytes we're willing to accept.
+		if int64(len(frag)) > int64(2*remainSize) {
+			if VerboseLogs {
+				log.Printf("http2: header list too large")
+			}
+			// It would be nice to send a RST_STREAM before sending the GOAWAY,
+			// but the struture of the server's frame writer makes this difficult.
+			return nil, ConnectionError(ErrCodeProtocol)
+		}
+
+		// Also close the connection after any CONTINUATION frame following an
+		// invalid header, since we stop tracking the size of the headers after
+		// an invalid one.
+		if invalid != nil {
+			if VerboseLogs {
+				log.Printf("http2: invalid header: %v", invalid)
+			}
+			// It would be nice to send a RST_STREAM before sending the GOAWAY,
+			// but the struture of the server's frame writer makes this difficult.
+			return nil, ConnectionError(ErrCodeProtocol)
+		}
+
 		if _, err := hdec.Write(frag); err != nil {
 			return nil, ConnectionError(ErrCodeCompression)
 		}
-- 
2.48.1