caddyfile: Fix errors caught by fuzzing (caddyserver#2097)

* caddyfile: More robust parsing for 'import' (fixes caddyserver#2096)

The fix for hanging involves limiting the number of wildcards in an
import pattern to just 1. Otherwise some patterns can expand to the
entire disk.

The other fix requires that the end string for an environment variable
expansion come after the start string.

* caddyfile: Fix more fuzzing errors

caddyfile/parse.go

@@ -263,14 +263,19 @@ func (p *parser) doImport() error {
 		} else {
 			globPattern = importPattern
 		}
+		if strings.Count(globPattern, "*") > 1 || strings.Count(globPattern, "?") > 1 ||
+			(strings.Contains(globPattern, "[") && strings.Contains(globPattern, "]")) {
+			// See issue #2096 - a pattern with many glob expansions can hang for too long
+			return p.Errf("Glob pattern may only contain one wildcard (*), but has others: %s", globPattern)
+		}
 		matches, err = filepath.Glob(globPattern)
 
 		if err != nil {
 			return p.Errf("Failed to use import pattern %s: %v", importPattern, err)
 		}
 		if len(matches) == 0 {
-			if strings.Contains(globPattern, "*") {
-				log.Printf("[WARNING] No files matching import pattern: %s", importPattern)
+			if strings.ContainsAny(globPattern, "*?[]") {
+				log.Printf("[WARNING] No files matching import glob pattern: %s", importPattern)
 			} else {
 				return p.Errf("File to import not found: %s", importPattern)
 			}
@@ -440,7 +445,7 @@ func replaceEnvReferences(s, refStart, refEnd string) string {
 	index := strings.Index(s, refStart)
 	for index != -1 {
 		endIndex := strings.Index(s, refEnd)
-		if endIndex != -1 {
+		if endIndex > index+len(refStart) {
 			ref := s[index : endIndex+len(refEnd)]
 			s = strings.Replace(s, ref, os.Getenv(ref[len(refStart):len(ref)-len(refEnd)]), -1)
 		} else {

caddyfile/parse_test.go

@@ -228,6 +228,17 @@ func TestParseOneAndImport(t *testing.T) {
 		{`""`, false, []string{}, map[string]int{}},
 
 		{``, false, []string{}, map[string]int{}},
+
+		// test cases found by fuzzing!
+		{`import }{$"`, true, []string{}, map[string]int{}},
+		{`import /*/*.txt`, true, []string{}, map[string]int{}},
+		{`import /???/?*?o`, true, []string{}, map[string]int{}},
+		{`import /??`, true, []string{}, map[string]int{}},
+		{`import /[a-z]`, true, []string{}, map[string]int{}},
+		{`import {$}`, true, []string{}, map[string]int{}},
+		{`import {%}`, true, []string{}, map[string]int{}},
+		{`import {$$}`, true, []string{}, map[string]int{}},
+		{`import {%%}`, true, []string{}, map[string]int{}},
 	} {
 		result, err := testParseOne(test.input)