[PATCH 3/9] libsepol: resolve GCC warning about null-dereference

[Christian Göttsche <cgzones@xxxxxxxxxxxxxx>]

GCC reports a NULL dereference of the return value of stack_peek(). This
function explicitly returns NULL in case of 'stack->pos == -1'.

Error out on NULL returned.

    module_to_cil.c: In function ‘block_to_cil’:
    module_to_cil.c:3357:55: error: potential null pointer dereference [-Werror=null-dereference]
     3357 |         struct list *alias_list = typealias_lists[decl->decl_id];
          |                                                   ~~~~^~~~~~~~~

There are more occurrences of unconditionally dereferencing the return
value of stack_peek(), but the callers should ensure a valid stack, so
just silence this single warning.

Signed-off-by: Christian Göttsche <cgzones@xxxxxxxxxxxxxx>
---
 libsepol/src/module_to_cil.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/libsepol/src/module_to_cil.c b/libsepol/src/module_to_cil.c
index 3c8ba10a..16e4004e 100644
--- a/libsepol/src/module_to_cil.c
+++ b/libsepol/src/module_to_cil.c
@@ -3354,9 +3354,14 @@ static int typealiases_to_cil(int indent, struct policydb *pdb, struct avrule_bl
 	char *type_name;
 	struct list_node *curr;
 	struct avrule_decl *decl = stack_peek(decl_stack);
-	struct list *alias_list = typealias_lists[decl->decl_id];
+	struct list *alias_list;
 	int rc = -1;
 
+	if (decl == NULL) {
+		return -1;
+	}
+
+	alias_list = typealias_lists[decl->decl_id];
 	if (alias_list == NULL) {
 		return 0;
 	}
-- 
2.33.0