From: Michael Anthony Knyszek <mknyszek@google.com>
Date: Tue, 4 Apr 2023 22:07:09 +0000 (+0000)
Subject: html/template,mime/multipart: document new GODEBUG settings
X-Git-Tag: go1.21rc1~1035
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=0d719823af1343f9921ee0293596f09e36ced0e4;p=gostls13.git

html/template,mime/multipart: document new GODEBUG settings

This change documents the new GODEBUG settings introduced for
html/template and mime/multipart, released with Go 1.19.8 and Go 1.20.3
as part of a security fix.

Updates #59153.
Updates #59234.

Change-Id: I25f4d8245da3301dccccfb44da8ff1a5985392a4
Reviewed-on: https://go-review.googlesource.com/c/go/+/482238
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
---

diff --git a/doc/godebug.md b/doc/godebug.md
index 44f5dfd16d..d760e0f4ef 100644
--- a/doc/godebug.md
+++ b/doc/godebug.md
@@ -130,7 +130,19 @@ and the [go command documentation](/cmd/go#hdr-Build_and_test_caching).
 
 Go 1.21 made it a run-time error to call `panic` with a nil interface value,
 controlled by the [`panicnil` setting](/pkg/builtin/#panic).
-There is no plan to remove this setting.
+
+Go 1.21 made it an error for html/template actions to appear inside of an ECMAScript 6
+template literal, controlled by the
+[`jstmpllitinterp` setting](/pkg/html/template#hdr-Security_Model).
+This behavior was backported to Go 1.19.8+ and Go 1.20.3+.
+
+Go 1.21 introduced a limit on the maximum number of MIME headers and multipart
+forms, controlled by the
+[`multipartmaxheaders` and `multipartmaxparts` settings](/pkg/mime/multipart#hdr-Limits)
+respectively.
+This behavior was backported to Go 1.19.8+ and Go 1.20.3+.
+
+There is no plan to remove any of these settings.
 
 ### Go 1.20
 
diff --git a/src/html/template/doc.go b/src/html/template/doc.go
index 57990e8a38..672d42ba32 100644
--- a/src/html/template/doc.go
+++ b/src/html/template/doc.go
@@ -231,5 +231,12 @@ Least Surprise Property:
 "A developer (or code reviewer) familiar with HTML, CSS, and JavaScript, who
 knows that contextual autoescaping happens should be able to look at a {{.}}
 and correctly infer what sanitization happens."
+
+As a consequence of the Least Surprise Property, template actions within an
+ECMAScript 6 template literal are disabled by default.
+Handling string interpolation within these literals is rather complex resulting
+in no clear safe way to support it.
+To re-enable template actions within ECMAScript 6 template literals, use the
+GODEBUG=jstmpllitinterp=1 environment variable.
 */
 package template
diff --git a/src/mime/multipart/multipart.go b/src/mime/multipart/multipart.go
index 98d48e2bdd..da1f45810e 100644
--- a/src/mime/multipart/multipart.go
+++ b/src/mime/multipart/multipart.go
@@ -9,6 +9,21 @@ Package multipart implements MIME multipart parsing, as defined in RFC
 
 The implementation is sufficient for HTTP (RFC 2388) and the multipart
 bodies generated by popular browsers.
+
+# Limits
+
+To protect against malicious inputs, this package sets limits on the size
+of the MIME data it processes.
+
+Reader.NextPart and Reader.NextRawPart limit the number of headers in a
+part to 10000 and Reader.ReadForm limits the total number of headers in all
+FileHeaders to 10000.
+These limits may be adjusted with the GODEBUG=multipartmaxheaders=<values>
+setting.
+
+Reader.ReadForm further limits the number of parts in a form to 1000.
+This limit may be adjusted with the GODEBUG=multipartmaxparts=<value>
+setting.
 */
 package multipart