go/doc: fix incorrect identifier parsing in comments

This code was trying to iterate codepoints, but didn't reslice the string,
so it was reading the first codepoint over and over, if the string length was
not a multiple of the first codepoint length, this would cause to overshoot
past the end of the string.

This was a latent bug introduced in CL 384265 but was revealed to
Ngolo-fuzzing in OSS-Fuzz in CL 397277.

Fixes #52353

Change-Id: I13f0352e6ad13a42878927f3b1c18c58360dd40c
GitHub-Last-Rev: 424f6cfad1bc7d66314911e6b4b4ce6751330435
GitHub-Pull-Request: golang/go#52356
Reviewed-on: https://go-review.googlesource.com/c/go/+/400240
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>

diff --git a/src/go/doc/comment/parse.go b/src/go/doc/comment/parse.go
index a8cba90ec0c06a16c422605a3ea0d5fddd700d45..83b37c32c53b8ad47079cff41ba0ffb4ffd13a11 100644 (file)
--- a/src/go/doc/comment/parse.go
+++ b/src/go/doc/comment/parse.go
@@ -1063,7 +1063,7 @@ func ident(s string) (id string, ok bool) {
                        }
                        break
                }
-               r, nr := utf8.DecodeRuneInString(s)
+               r, nr := utf8.DecodeRuneInString(s[n:])
                if unicode.IsLetter(r) {
                        n += nr
                        continue

diff --git a/src/go/doc/comment/parse_test.go b/src/go/doc/comment/parse_test.go
new file mode 100644 (file)
index 0000000..bce733e
--- /dev/null
+++ b/src/go/doc/comment/parse_test.go
@@ -0,0 +1,12 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package comment
+
+import "testing"
+
+// See https://golang.org/issue/52353
+func Test52353(t *testing.T) {
+       ident("𫕐ﯯ")
+}