io/fs: fix stack exhaustion in Glob

A limit is added to the number of path separators allowed by an input to
Glob, to prevent stack exhaustion issues.

Thanks to Juho Nurminen of Mattermost who reported a similar issue in
path/filepath.

Fixes CVE-2022-30630
Fixes golang/go#53415

Change-Id: I5a9d02591fed90cd3d52627f5945f1301e53465d
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/1497588
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/417065
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>

src/io/fs/glob.go

diff --git a/src/io/fs/glob.go b/src/io/fs/glob.go
index 45d9cb6..0e529cd 100644
--- a/src/io/fs/glob.go
+++ b/src/io/fs/glob.go
@@ -31,6 +31,16 @@
 // Otherwise, Glob uses ReadDir to traverse the directory tree
 // and look for matches for the pattern.
 func Glob(fsys FS, pattern string) (matches []string, err error) {
+	return globWithLimit(fsys, pattern, 0)
+}
+
+func globWithLimit(fsys FS, pattern string, depth int) (matches []string, err error) {
+	// This limit is added to prevent stack exhaustion issues. See
+	// CVE-2022-30630.
+	const pathSeparatorsLimit = 10000
+	if depth > pathSeparatorsLimit {
+		return nil, path.ErrBadPattern
+	}
 	if fsys, ok := fsys.(GlobFS); ok {
 		return fsys.Glob(pattern)
 	}
@@ -59,9 +69,9 @@
 	}
 
 	var m []string
-	m, err = Glob(fsys, dir)
+	m, err = globWithLimit(fsys, dir, depth+1)
 	if err != nil {
-		return
+		return nil, err
 	}
 	for _, d := range m {
 		matches, err = glob(fsys, d, file, matches)

src/io/fs/glob_test.go

diff --git a/src/io/fs/glob_test.go b/src/io/fs/glob_test.go
index f19bebe..d052eab 100644
--- a/src/io/fs/glob_test.go
+++ b/src/io/fs/glob_test.go
@@ -8,6 +8,7 @@
 	. "io/fs"
 	"os"
 	"path"
+	"strings"
 	"testing"
 )
 
@@ -55,6 +56,15 @@
 	}
 }
 
+func TestCVE202230630(t *testing.T) {
+	// Prior to CVE-2022-30630, a stack exhaustion would occur given a large
+	// number of separators. There is now a limit of 10,000.
+	_, err := Glob(os.DirFS("."), "/*"+strings.Repeat("/", 10001))
+	if err != path.ErrBadPattern {
+		t.Fatalf("Glob returned err=%v, want %v", err, path.ErrBadPattern)
+	}
+}
+
 // contains reports whether vector contains the string s.
 func contains(vector []string, s string) bool {
 	for _, elem := range vector {