vm: fix invalid memory access on GC'ing uninitialized VM context

When attempting to invoke uc_vm_free() or uc_gc() on a uc_vm_t struct
that has not been initialized by uc_vm_init(), the circular double
linked value list is not set up, causing the GC to read invalid memory
locations when attempting to traverse the object list.

Back out early when the list heads are not properly set up in order to
prevent this issue.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

1 files changed, 4 insertions, 0 deletions

diff --git a/types.c b/types.c
index 98547e3..5808d8e 100644
--- a/types.c
+++ b/types.c
@@ -1763,6 +1763,10 @@ ucv_gc(uc_vm_t *vm, bool final)
 	uc_value_t *val;
 	size_t i;
 
+	/* back out early if value list is uninitialized */
+	if (!vm->values.prev || !vm->values.next)
+		return;
+
 	if (!final) {
 		/* mark reachable objects */
 		ucv_gc_mark(vm->globals);