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[release-branch.go1.22] html/template: escape additional tokens in Ma…
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…rshalJSON errors

Escape "</script" and "<!--" in errors returned from MarshalJSON errors
when attempting to marshal types in script blocks. This prevents any
user controlled content from prematurely terminating the script block.

Updates golang#65697
Fixes golang#65969

Change-Id: Icf0e26c54ea7d9c1deed0bff11b6506c99ddef1b
Reviewed-on: https://go-review.googlesource.com/c/go/+/564196
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
(cherry picked from commit ccbc725)
Reviewed-on: https://go-review.googlesource.com/c/go/+/567535
Reviewed-by: Carlos Amedee <carlos@golang.org>
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@rolandshoemaker @romaindoumenc
rolandshoemaker authored and romaindoumenc committed Mar 6, 2024
1 parent 7880412 commit 16afdc0
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22 changes: 20 additions & 2 deletions src/html/template/js.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -171,13 +171,31 @@ func jsValEscaper(args ...any) string {
// cyclic data. This may be an unacceptable DoS risk.
b, err := json.Marshal(a)
if err != nil {
// Put a space before comment so that if it is flush against
// While the standard JSON marshaller does not include user controlled
// information in the error message, if a type has a MarshalJSON method,
// the content of the error message is not guaranteed. Since we insert
// the error into the template, as part of a comment, we attempt to
// prevent the error from either terminating the comment, or the script
// block itself.
//
// In particular we:
// * replace "*/" comment end tokens with "* /", which does not
// terminate the comment
// * replace "</script" with "\x3C/script", and "<!--" with
// "\x3C!--", which prevents confusing script block termination
// semantics
//
// We also put a space before the comment so that if it is flush against
// a division operator it is not turned into a line comment:
// x/{{y}}
// turning into
// x//* error marshaling y:
// second line of error message */null
return fmt.Sprintf(" /* %s */null ", strings.ReplaceAll(err.Error(), "*/", "* /"))
errStr := err.Error()
errStr = strings.ReplaceAll(errStr, "*/", "* /")
errStr = strings.ReplaceAll(errStr, "</script", `\x3C/script`)
errStr = strings.ReplaceAll(errStr, "<!--", `\x3C!--`)
return fmt.Sprintf(" /* %s */null ", errStr)
}

// TODO: maybe post-process output to prevent it from containing
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96 changes: 54 additions & 42 deletions src/html/template/js_test.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
package template

import (
"errors"
"math"
"strings"
"testing"
Expand Down Expand Up @@ -103,61 +104,72 @@ func TestNextJsCtx(t *testing.T) {
}
}

type jsonErrType struct{}

func (e *jsonErrType) MarshalJSON() ([]byte, error) {
return nil, errors.New("beep */ boop </script blip <!--")
}

func TestJSValEscaper(t *testing.T) {
tests := []struct {
x any
js string
x any
js string
skipNest bool
}{
{int(42), " 42 "},
{uint(42), " 42 "},
{int16(42), " 42 "},
{uint16(42), " 42 "},
{int32(-42), " -42 "},
{uint32(42), " 42 "},
{int16(-42), " -42 "},
{uint16(42), " 42 "},
{int64(-42), " -42 "},
{uint64(42), " 42 "},
{uint64(1) << 53, " 9007199254740992 "},
{int(42), " 42 ", false},
{uint(42), " 42 ", false},
{int16(42), " 42 ", false},
{uint16(42), " 42 ", false},
{int32(-42), " -42 ", false},
{uint32(42), " 42 ", false},
{int16(-42), " -42 ", false},
{uint16(42), " 42 ", false},
{int64(-42), " -42 ", false},
{uint64(42), " 42 ", false},
{uint64(1) << 53, " 9007199254740992 ", false},
// ulp(1 << 53) > 1 so this loses precision in JS
// but it is still a representable integer literal.
{uint64(1)<<53 + 1, " 9007199254740993 "},
{float32(1.0), " 1 "},
{float32(-1.0), " -1 "},
{float32(0.5), " 0.5 "},
{float32(-0.5), " -0.5 "},
{float32(1.0) / float32(256), " 0.00390625 "},
{float32(0), " 0 "},
{math.Copysign(0, -1), " -0 "},
{float64(1.0), " 1 "},
{float64(-1.0), " -1 "},
{float64(0.5), " 0.5 "},
{float64(-0.5), " -0.5 "},
{float64(0), " 0 "},
{math.Copysign(0, -1), " -0 "},
{"", `""`},
{"foo", `"foo"`},
{uint64(1)<<53 + 1, " 9007199254740993 ", false},
{float32(1.0), " 1 ", false},
{float32(-1.0), " -1 ", false},
{float32(0.5), " 0.5 ", false},
{float32(-0.5), " -0.5 ", false},
{float32(1.0) / float32(256), " 0.00390625 ", false},
{float32(0), " 0 ", false},
{math.Copysign(0, -1), " -0 ", false},
{float64(1.0), " 1 ", false},
{float64(-1.0), " -1 ", false},
{float64(0.5), " 0.5 ", false},
{float64(-0.5), " -0.5 ", false},
{float64(0), " 0 ", false},
{math.Copysign(0, -1), " -0 ", false},
{"", `""`, false},
{"foo", `"foo"`, false},
// Newlines.
{"\r\n\u2028\u2029", `"\r\n\u2028\u2029"`},
{"\r\n\u2028\u2029", `"\r\n\u2028\u2029"`, false},
// "\v" == "v" on IE 6 so use "\u000b" instead.
{"\t\x0b", `"\t\u000b"`},
{struct{ X, Y int }{1, 2}, `{"X":1,"Y":2}`},
{[]any{}, "[]"},
{[]any{42, "foo", nil}, `[42,"foo",null]`},
{[]string{"<!--", "</script>", "-->"}, `["\u003c!--","\u003c/script\u003e","--\u003e"]`},
{"<!--", `"\u003c!--"`},
{"-->", `"--\u003e"`},
{"<![CDATA[", `"\u003c![CDATA["`},
{"]]>", `"]]\u003e"`},
{"</script", `"\u003c/script"`},
{"\U0001D11E", "\"\U0001D11E\""}, // or "\uD834\uDD1E"
{nil, " null "},
{"\t\x0b", `"\t\u000b"`, false},
{struct{ X, Y int }{1, 2}, `{"X":1,"Y":2}`, false},
{[]any{}, "[]", false},
{[]any{42, "foo", nil}, `[42,"foo",null]`, false},
{[]string{"<!--", "</script>", "-->"}, `["\u003c!--","\u003c/script\u003e","--\u003e"]`, false},
{"<!--", `"\u003c!--"`, false},
{"-->", `"--\u003e"`, false},
{"<![CDATA[", `"\u003c![CDATA["`, false},
{"]]>", `"]]\u003e"`, false},
{"</script", `"\u003c/script"`, false},
{"\U0001D11E", "\"\U0001D11E\"", false}, // or "\uD834\uDD1E"
{nil, " null ", false},
{&jsonErrType{}, " /* json: error calling MarshalJSON for type *template.jsonErrType: beep * / boop \\x3C/script blip \\x3C!-- */null ", true},
}

for _, test := range tests {
if js := jsValEscaper(test.x); js != test.js {
t.Errorf("%+v: want\n\t%q\ngot\n\t%q", test.x, test.js, js)
}
if test.skipNest {
continue
}
// Make sure that escaping corner cases are not broken
// by nesting.
a := []any{test.x}
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