go/scanner: reject large line and column numbers in //line directives

Setting a large line or column number using a //line directive can cause
integer overflow even in small source files.

Limit line and column numbers in //line directives to 2^30-1, which
is small enough to avoid int32 overflow on all reasonbly-sized files.

For #59180
Fixes CVE-2023-24537

Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1802456
Reviewed-by: Julie Qiu <julieqiu@google.com>
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Run-TryBot: Damien Neil <dneil@google.com>
Change-Id: I149bf34deca532af7994203fa1e6aca3c890ea14
Reviewed-on: https://go-review.googlesource.com/c/go/+/482078
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Bypass: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>

src/go/parser/parser_test.go

@@ -764,3 +764,19 @@ func TestRangePos(t *testing.T) {
 		})
 	}
 }
+
+// TestIssue59180 tests that line number overflow doesn't cause an infinite loop.
+func TestIssue59180(t *testing.T) {
+	testcases := []string{
+		"package p\n//line :9223372036854775806\n\n//",
+		"package p\n//line :1:9223372036854775806\n\n//",
+		"package p\n//line file:9223372036854775806\n\n//",
+	}
+
+	for _, src := range testcases {
+		_, err := ParseFile(token.NewFileSet(), "", src, ParseComments)
+		if err == nil {
+			t.Errorf("ParseFile(%s) succeeded unexpectedly", src)
+		}
+	}
+}

src/go/scanner/scanner.go

@@ -253,13 +253,16 @@ func (s *Scanner) updateLineInfo(next, offs int, text []byte) {
 		return
 	}
 
+	// Put a cap on the maximum size of line and column numbers.
+	// 30 bits allows for some additional space before wrapping an int32.
+	const maxLineCol = 1<<30 - 1
 	var line, col int
 	i2, n2, ok2 := trailingDigits(text[:i-1])
 	if ok2 {
 		//line filename:line:col
 		i, i2 = i2, i
 		line, col = n2, n
-		if col == 0 {
+		if col == 0 || col > maxLineCol {
 			s.error(offs+i2, "invalid column number: "+string(text[i2:]))
 			return
 		}
@@ -269,7 +272,7 @@ func (s *Scanner) updateLineInfo(next, offs int, text []byte) {
 		line = n
 	}
 
-	if line == 0 {
+	if line == 0 || line > maxLineCol {
 		s.error(offs+i, "invalid line number: "+string(text[i:]))
 		return
 	}