Return per-certificate chain if extra chain is NULL.

If an application calls the macro SSL_CTX_get_extra_chain_certs
return either the old "shared" extra certificates or those associated
with the current certificate.

This means applications which call SSL_CTX_use_certificate_chain_file
and retrieve the additional chain using SSL_CTX_get_extra_chain_certs
will still work. An application which only wants to check the shared
extra certificates can call the new macro
SSL_CTX_get_extra_chain_certs_only

(Imported from upstream's e0d4272a58 and
3bff195dca)

ssl/s3_lib.c

@@ -3586,7 +3586,10 @@ long ssl3_ctx_ctrl(SSL_CTX *ctx, int cmd, long larg, void *parg)
 		break;
 
 	case SSL_CTRL_GET_EXTRA_CHAIN_CERTS:
-		*(STACK_OF(X509) **)parg =  ctx->extra_certs;
+		if (ctx->extra_certs == NULL && larg == 0)
+			*(STACK_OF(X509) **)parg =  ctx->cert->key->chain;
+		else
+			*(STACK_OF(X509) **)parg =  ctx->extra_certs;
 		break;
 
 	case SSL_CTRL_CLEAR_EXTRA_CHAIN_CERTS:

ssl/ssl.h

@@ -2020,6 +2020,8 @@ DECLARE_PEM_rw(SSL_SESSION, SSL_SESSION)
 	SSL_CTX_ctrl(ctx,SSL_CTRL_EXTRA_CHAIN_CERT,0,(char *)x509)
 #define SSL_CTX_get_extra_chain_certs(ctx,px509) \
 	SSL_CTX_ctrl(ctx,SSL_CTRL_GET_EXTRA_CHAIN_CERTS,0,px509)
+#define SSL_CTX_get_extra_chain_certs_only(ctx,px509) \
+	SSL_CTX_ctrl(ctx,SSL_CTRL_GET_EXTRA_CHAIN_CERTS,1,px509)
 #define SSL_CTX_clear_extra_chain_certs(ctx) \
 	SSL_CTX_ctrl(ctx,SSL_CTRL_CLEAR_EXTRA_CHAIN_CERTS,0,NULL)