Limit nesting depth

iter.go

@@ -74,6 +74,7 @@ type Iterator struct {
 	buf              []byte
 	head             int
 	tail             int
+	depth            int
 	captureStartedAt int
 	captured         []byte
 	Error            error
@@ -88,6 +89,7 @@ func NewIterator(cfg API) *Iterator {
 		buf:    nil,
 		head:   0,
 		tail:   0,
+		depth:  0,
 	}
 }
 
@@ -99,6 +101,7 @@ func Parse(cfg API, reader io.Reader, bufSize int) *Iterator {
 		buf:    make([]byte, bufSize),
 		head:   0,
 		tail:   0,
+		depth:  0,
 	}
 }
 
@@ -110,6 +113,7 @@ func ParseBytes(cfg API, input []byte) *Iterator {
 		buf:    input,
 		head:   0,
 		tail:   len(input),
+		depth:  0,
 	}
 }
 
@@ -128,6 +132,7 @@ func (iter *Iterator) Reset(reader io.Reader) *Iterator {
 	iter.reader = reader
 	iter.head = 0
 	iter.tail = 0
+	iter.depth = 0
 	return iter
 }
 
@@ -137,6 +142,7 @@ func (iter *Iterator) ResetBytes(input []byte) *Iterator {
 	iter.buf = input
 	iter.head = 0
 	iter.tail = len(input)
+	iter.depth = 0
 	return iter
 }
 
@@ -320,3 +326,24 @@ func (iter *Iterator) Read() interface{} {
 		return nil
 	}
 }
+
+// limit maximum depth of nesting, as allowed by https://tools.ietf.org/html/rfc7159#section-9
+const maxDepth = 10000
+
+func (iter *Iterator) incrementDepth() (success bool) {
+	iter.depth++
+	if iter.depth <= maxDepth {
+		return true
+	}
+	iter.ReportError("incrementDepth", "exceeded max depth")
+	return false
+}
+
+func (iter *Iterator) decrementDepth() (success bool) {
+	iter.depth--
+	if iter.depth >= 0 {
+		return true
+	}
+	iter.ReportError("decrementDepth", "unexpected negative nesting")
+	return false
+}

iter_array.go

@@ -28,26 +28,32 @@ func (iter *Iterator) ReadArray() (ret bool) {
 func (iter *Iterator) ReadArrayCB(callback func(*Iterator) bool) (ret bool) {
 	c := iter.nextToken()
 	if c == '[' {
+		if !iter.incrementDepth() {
+			return false
+		}
 		c = iter.nextToken()
 		if c != ']' {
 			iter.unreadByte()
 			if !callback(iter) {
+				iter.decrementDepth()
 				return false
 			}
 			c = iter.nextToken()
 			for c == ',' {
 				if !callback(iter) {
+					iter.decrementDepth()
 					return false
 				}
 				c = iter.nextToken()
 			}
 			if c != ']' {
 				iter.ReportError("ReadArrayCB", "expect ] in the end, but found "+string([]byte{c}))
+				iter.decrementDepth()
 				return false
 			}
-			return true
+			return iter.decrementDepth()
 		}
-		return true
+		return iter.decrementDepth()
 	}
 	if c == 'n' {
 		iter.skipThreeBytes('u', 'l', 'l')

iter_object.go

@@ -112,6 +112,9 @@ func (iter *Iterator) ReadObjectCB(callback func(*Iterator, string) bool) bool {
 	c := iter.nextToken()
 	var field string
 	if c == '{' {
+		if !iter.incrementDepth() {
+			return false
+		}
 		c = iter.nextToken()
 		if c == '"' {
 			iter.unreadByte()
@@ -121,6 +124,7 @@ func (iter *Iterator) ReadObjectCB(callback func(*Iterator, string) bool) bool {
 				iter.ReportError("ReadObject", "expect : after object field, but found "+string([]byte{c}))
 			}
 			if !callback(iter, field) {
+				iter.decrementDepth()
 				return false
 			}
 			c = iter.nextToken()
@@ -131,20 +135,23 @@ func (iter *Iterator) ReadObjectCB(callback func(*Iterator, string) bool) bool {
 					iter.ReportError("ReadObject", "expect : after object field, but found "+string([]byte{c}))
 				}
 				if !callback(iter, field) {
+					iter.decrementDepth()
 					return false
 				}
 				c = iter.nextToken()
 			}
 			if c != '}' {
 				iter.ReportError("ReadObjectCB", `object not ended with }`)
+				iter.decrementDepth()
 				return false
 			}
-			return true
+			return iter.decrementDepth()
 		}
 		if c == '}' {
-			return true
+			return iter.decrementDepth()
 		}
 		iter.ReportError("ReadObjectCB", `expect " after }, but found `+string([]byte{c}))
+		iter.decrementDepth()
 		return false
 	}
 	if c == 'n' {
@@ -159,39 +166,48 @@ func (iter *Iterator) ReadObjectCB(callback func(*Iterator, string) bool) bool {
 func (iter *Iterator) ReadMapCB(callback func(*Iterator, string) bool) bool {
 	c := iter.nextToken()
 	if c == '{' {
+		if !iter.incrementDepth() {
+			return false
+		}
 		c = iter.nextToken()
 		if c == '"' {
 			iter.unreadByte()
 			field := iter.ReadString()
 			if iter.nextToken() != ':' {
 				iter.ReportError("ReadMapCB", "expect : after object field, but found "+string([]byte{c}))
+				iter.decrementDepth()
 				return false
 			}
 			if !callback(iter, field) {
+				iter.decrementDepth()
 				return false
 			}
 			c = iter.nextToken()
 			for c == ',' {
 				field = iter.ReadString()
 				if iter.nextToken() != ':' {
 					iter.ReportError("ReadMapCB", "expect : after object field, but found "+string([]byte{c}))
+					iter.decrementDepth()
 					return false
 				}
 				if !callback(iter, field) {
+					iter.decrementDepth()
 					return false
 				}
 				c = iter.nextToken()
 			}
 			if c != '}' {
 				iter.ReportError("ReadMapCB", `object not ended with }`)
+				iter.decrementDepth()
 				return false
 			}
-			return true
+			return iter.decrementDepth()
 		}
 		if c == '}' {
-			return true
+			return iter.decrementDepth()
 		}
 		iter.ReportError("ReadMapCB", `expect " after }, but found `+string([]byte{c}))
+		iter.decrementDepth()
 		return false
 	}
 	if c == 'n' {

iter_skip_sloppy.go

@@ -22,6 +22,9 @@ func (iter *Iterator) skipNumber() {
 
 func (iter *Iterator) skipArray() {
 	level := 1
+	if !iter.incrementDepth() {
+		return
+	}
 	for {
 		for i := iter.head; i < iter.tail; i++ {
 			switch iter.buf[i] {
@@ -31,8 +34,14 @@ func (iter *Iterator) skipArray() {
 				i = iter.head - 1 // it will be i++ soon
 			case '[': // If open symbol, increase level
 				level++
+				if !iter.incrementDepth() {
+					return
+				}
 			case ']': // If close symbol, increase level
 				level--
+				if !iter.decrementDepth() {
+					return
+				}
 
 				// If we have returned to the original level, we're done
 				if level == 0 {
@@ -50,6 +59,10 @@ func (iter *Iterator) skipArray() {
 
 func (iter *Iterator) skipObject() {
 	level := 1
+	if !iter.incrementDepth() {
+		return
+	}
+
 	for {
 		for i := iter.head; i < iter.tail; i++ {
 			switch iter.buf[i] {
@@ -59,8 +72,14 @@ func (iter *Iterator) skipObject() {
 				i = iter.head - 1 // it will be i++ soon
 			case '{': // If open symbol, increase level
 				level++
+				if !iter.incrementDepth() {
+					return
+				}
 			case '}': // If close symbol, increase level
 				level--
+				if !iter.decrementDepth() {
+					return
+				}
 
 				// If we have returned to the original level, we're done
 				if level == 0 {