All the little functions created by the IMPLEMENT_STACK_OF() macro will

cast their type-specific STACK into a real STACK and call the underlying
sk_*** function. The problem is that if the STACK_OF(..) parameter being
passed in has a "const *" qualifier, it is discarded by the cast.

I'm currently implementing a fix for this but in the mean-time, this is
one case I noticed (a few type-specific sk_**_num() functions pass in
const type-specific stacks). If there are other errors in the code where
consts are being discarded, we will similarly not notice them. yuck.

crypto/stack/stack.h

@@ -79,7 +79,7 @@ typedef struct stack_st
 #define M_sk_num(sk)		((sk) ? (sk)->num:-1)
 #define M_sk_value(sk,n)	((sk) ? (sk)->data[n] : NULL)
 
-int sk_num(STACK *);
+int sk_num(const STACK *);
 char *sk_value(STACK *, int);
 
 char *sk_set(STACK *, int, char *);