feat: keep alive structs for C usage

When accessing C fields or functions, there was a potential race
condition with the garbage collector running the finalizer if
the object was no longer referenced elsewhere. This race was
(mostly) short, but arguably still existed.
Use KeepAlive() to safeguard these accesses and ensure the object
is only garbage collected (and the C part freed) once the access
has finished.

rule.go

@@ -107,7 +107,10 @@ static void get_rules(YR_RULES *ruleset, const YR_RULE *rules[], int *n) {
 
 */
 import "C"
-import "unsafe"
+import (
+	"runtime"
+	"unsafe"
+)
 
 // Rule represents a single rule as part of a ruleset.
 type Rule struct {
@@ -118,12 +121,16 @@ type Rule struct {
 
 // Identifier returns the rule's name.
 func (r *Rule) Identifier() string {
-	return C.GoString(C.rule_identifier(r.cptr))
+	id := C.GoString(C.rule_identifier(r.cptr))
+	runtime.KeepAlive(r)
+	return id
 }
 
 // Namespace returns the rule's namespace.
 func (r *Rule) Namespace() string {
-	return C.GoString(C.rule_namespace(r.cptr))
+	namespace := C.GoString(C.rule_namespace(r.cptr))
+	runtime.KeepAlive(r)
+	return namespace
 }
 
 // Tags returns the rule's tags.
@@ -138,6 +145,7 @@ func (r *Rule) Tags() (tags []string) {
 	for _, t := range tagptrs {
 		tags = append(tags, C.GoString(t))
 	}
+	runtime.KeepAlive(r)
 	return
 }
 
@@ -173,17 +181,22 @@ func (r *Rule) Metas() (metas []Meta) {
 		}
 		metas = append(metas, Meta{id, val})
 	}
+	runtime.KeepAlive(r)
 	return
 }
 
 // IsPrivate returns true if the rule is marked as private.
 func (r *Rule) IsPrivate() bool {
-	return r.cptr.flags&C.RULE_FLAGS_PRIVATE != 0
+	private := r.cptr.flags&C.RULE_FLAGS_PRIVATE != 0
+	runtime.KeepAlive(r)
+	return private
 }
 
 // IsGlobal returns true if the rule is marked as global.
 func (r *Rule) IsGlobal() bool {
-	return r.cptr.flags&C.RULE_FLAGS_GLOBAL != 0
+	global := r.cptr.flags&C.RULE_FLAGS_GLOBAL != 0
+	runtime.KeepAlive(r)
+	return global
 }
 
 // String represents a string as part of a rule.
@@ -210,7 +223,9 @@ func (r *Rule) Strings() (strs []String) {
 
 // Identifier returns the string's name.
 func (s *String) Identifier() string {
-	return C.GoString(C.string_identifier(s.cptr))
+	id := C.GoString(C.string_identifier(s.cptr))
+	runtime.KeepAlive(s)
+	return id
 }
 
 // Match represents a string match.
@@ -241,12 +256,16 @@ func (s *String) Matches(sc *ScanContext) (matches []Match) {
 // Base returns the base offset of the memory block in which the
 // string match occurred.
 func (m *Match) Base() int64 {
-	return int64(m.cptr.base)
+	base := int64(m.cptr.base)
+	runtime.KeepAlive(m)
+	return base
 }
 
 // Offset returns the offset at which the string match occurred.
 func (m *Match) Offset() int64 {
-	return int64(m.cptr.offset)
+	offset := int64(m.cptr.offset)
+	runtime.KeepAlive(m)
+	return offset
 }
 
 // XorKey returns the XOR value with which the string match occurred.
@@ -256,7 +275,9 @@ func (m *Match) XorKey() uint8 {
 
 // Data returns the blob of data associated with the string match.
 func (m *Match) Data() []byte {
-	return C.GoBytes(unsafe.Pointer(m.cptr.data), C.int(m.cptr.data_length))
+	data := C.GoBytes(unsafe.Pointer(m.cptr.data), C.int(m.cptr.data_length))
+	runtime.KeepAlive(m)
+	return data
 }
 
 func (r *Rule) getMatchStrings(sc *ScanContext) (matchstrings []MatchString) {
@@ -277,11 +298,13 @@ func (r *Rule) getMatchStrings(sc *ScanContext) (matchstrings []MatchString) {
 // Enable enables a single rule.
 func (r *Rule) Enable() {
 	C.yr_rule_enable(r.cptr)
+	runtime.KeepAlive(r)
 }
 
 // Disable disables a single rule.
 func (r *Rule) Disable() {
 	C.yr_rule_disable(r.cptr)
+	runtime.KeepAlive(r)
 }
 
 // GetRules returns a slice of rule objects that are part of the

scanner.go

@@ -297,10 +297,12 @@ func (s *Scanner) GetProfilingInfo() (rpis []RuleProfilingInfo) {
 	for ; rpi.rule != nil; rpi = (*C.YR_RULE_PROFILING_INFO)(unsafe.Pointer(uintptr(unsafe.Pointer(rpi)) + unsafe.Sizeof(*rpi))) {
 		rpis = append(rpis, RuleProfilingInfo{Rule{rpi.rule, s.rules}, uint64(rpi.cost)})
 	}
+	runtime.KeepAlive(s)
 	return
 }
 
 // ResetProfilingInfo resets the Scanner's profiling information
 func (s *Scanner) ResetProfilingInfo() {
 	C.yr_scanner_reset_profiling_info(s.cptr)
+	runtime.KeepAlive(s)
 }