From d4c53812e6ce2ac368173d7fcd31d0ecfcffb002 Mon Sep 17 00:00:00 2001
From: Roland Shoemaker <bracewell@google.com>
Date: Thu, 20 Jun 2024 10:45:30 -0700
Subject: [PATCH] go/build/constraint: add parsing limits

Limit the size of build constraints that we will parse. This prevents a
number of stack exhaustions that can be hit when parsing overly complex
constraints. The imposed limits are unlikely to ever be hit in real
world usage.

Updates #69141
Fixes #69148
Fixes CVE-2024-34158

Change-Id: I38b614bf04caa36eefc6a4350d848588c4cef3c4
Reviewed-on: https://go-internal-review.googlesource.com/c/go/+/1540
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Russ Cox <rsc@google.com>
(cherry picked from commit 0c74dc9e0da0cf1e12494b514d822b5bebbc9f04)
Reviewed-on: https://go-internal-review.googlesource.com/c/go/+/1582
Reviewed-by: Tatiana Bradley <tatianabradley@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/611183
Auto-Submit: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
TryBot-Bypass: Dmitri Shuralyov <dmitshur@google.com>

CVE: CVE-2024-34158

Upstream-Status: Backport [https://github.com/golang/go/commit/d4c53812e6ce2ac368173d7fcd31d0ecfcffb002]

Signed-off-by: Archana Polampalli <archana.polampalli@windriver.com>
---
 src/go/build/constraint/expr.go      | 28 ++++++++++--
 src/go/build/constraint/expr_test.go | 65 +++++++++++++++++++++++++++-
 2 files changed, 89 insertions(+), 4 deletions(-)

diff --git a/src/go/build/constraint/expr.go b/src/go/build/constraint/expr.go
index 957eb9b..85897e2 100644
--- a/src/go/build/constraint/expr.go
+++ b/src/go/build/constraint/expr.go
@@ -18,6 +18,10 @@ import (
	"unicode/utf8"
 )

+// maxSize is a limit used to control the complexity of expressions, in order
+// to prevent stack exhaustion issues due to recursion.
+const maxSize = 1000
+
 // An Expr is a build tag constraint expression.
 // The underlying concrete type is *AndExpr, *OrExpr, *NotExpr, or *TagExpr.
 type Expr interface {
@@ -153,7 +157,7 @@ func Parse(line string) (Expr, error) {
		return parseExpr(text)
	}
	if text, ok := splitPlusBuild(line); ok {
-		return parsePlusBuildExpr(text), nil
+		return parsePlusBuildExpr(text)
	}
	return nil, errNotConstraint
 }
@@ -203,6 +207,8 @@ type exprParser struct {
	tok   string // last token read
	isTag bool
	pos   int // position (start) of last token
+
+	size int
 }

 // parseExpr parses a boolean build tag expression.
@@ -251,6 +257,10 @@ func (p *exprParser) and() Expr {
 // On entry, the next input token has not yet been lexed.
 // On exit, the next input token has been lexed and is in p.tok.
 func (p *exprParser) not() Expr {
+	p.size++
+	if p.size > maxSize {
+		panic(&SyntaxError{Offset: p.pos, Err: "build expression too large"})
+	}
	p.lex()
	if p.tok == "!" {
		p.lex()
@@ -391,7 +401,13 @@ func splitPlusBuild(line string) (expr string, ok bool) {
 }

 // parsePlusBuildExpr parses a legacy build tag expression (as used with “// +build”).
-func parsePlusBuildExpr(text string) Expr {
+func parsePlusBuildExpr(text string) (Expr, error) {
+	// Only allow up to 100 AND/OR operators for "old" syntax.
+	// This is much less than the limit for "new" syntax,
+	// but uses of old syntax were always very simple.
+	const maxOldSize = 100
+	size := 0
+
	var x Expr
	for _, clause := range strings.Fields(text) {
		var y Expr
@@ -417,19 +433,25 @@ func parsePlusBuildExpr(text string) Expr {
			if y == nil {
				y = z
			} else {
+				if size++; size > maxOldSize {
+					return nil, errComplex
+				}
				y = and(y, z)
			}
		}
		if x == nil {
			x = y
		} else {
+			if size++; size > maxOldSize {
+				return nil, errComplex
+			}
			x = or(x, y)
		}
	}
	if x == nil {
		x = tag("ignore")
	}
-	return x
+	return x, nil
 }

 // isValidTag reports whether the word is a valid build tag.
diff --git a/src/go/build/constraint/expr_test.go b/src/go/build/constraint/expr_test.go
index 15d1890..ac38ba6 100644
--- a/src/go/build/constraint/expr_test.go
+++ b/src/go/build/constraint/expr_test.go
@@ -222,7 +222,7 @@ var parsePlusBuildExprTests = []struct {
 func TestParsePlusBuildExpr(t *testing.T) {
	for i, tt := range parsePlusBuildExprTests {
		t.Run(fmt.Sprint(i), func(t *testing.T) {
-			x := parsePlusBuildExpr(tt.in)
+			x, _ := parsePlusBuildExpr(tt.in)
			if x.String() != tt.x.String() {
				t.Errorf("parsePlusBuildExpr(%q):\nhave %v\nwant %v", tt.in, x, tt.x)
			}
@@ -319,3 +319,66 @@ func TestPlusBuildLines(t *testing.T) {
		})
	}
 }
+
+func TestSizeLimits(t *testing.T) {
+	for _, tc := range []struct {
+		name string
+		expr string
+	}{
+		{
+			name: "go:build or limit",
+			expr: "//go:build " + strings.Repeat("a || ", maxSize+2),
+		},
+		{
+			name: "go:build and limit",
+			expr: "//go:build " + strings.Repeat("a && ", maxSize+2),
+		},
+		{
+			name: "go:build and depth limit",
+			expr: "//go:build " + strings.Repeat("(a &&", maxSize+2),
+		},
+		{
+			name: "go:build or depth limit",
+			expr: "//go:build " + strings.Repeat("(a ||", maxSize+2),
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := Parse(tc.expr)
+			if err == nil {
+				t.Error("expression did not trigger limit")
+			} else if syntaxErr, ok := err.(*SyntaxError); !ok || syntaxErr.Err != "build expression too large" {
+				if !ok {
+					t.Errorf("unexpected error: %v", err)
+				} else {
+					t.Errorf("unexpected syntax error: %s", syntaxErr.Err)
+				}
+			}
+		})
+	}
+}
+
+func TestPlusSizeLimits(t *testing.T) {
+	maxOldSize := 100
+	for _, tc := range []struct {
+		name string
+		expr string
+	}{
+		{
+			name: "+build or limit",
+			expr: "// +build " + strings.Repeat("a ", maxOldSize+2),
+		},
+		{
+			name: "+build and limit",
+			expr: "// +build " + strings.Repeat("a,", maxOldSize+2),
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := Parse(tc.expr)
+			if err == nil {
+				t.Error("expression did not trigger limit")
+			} else if err != errComplex {
+				t.Errorf("unexpected error: got %q, want %q", err, errComplex)
+			}
+		})
+	}
+}
--
2.40.0
