ENGINE_pkey_asn1_find_str(): don't assume an engine implements ASN1 method

Just because an engine implements algorithm methods, that doesn't mean
it also implements the ASN1 method.  Therefore, be careful when looking
for an ASN1 method among all engines, don't try to use one that doesn't
exist.

Fixes #6381

Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6383)

(cherry picked from commit 1ac3cd6277f880fac4df313702d5e3b3814e56e2)

diff --git a/crypto/engine/tb_asnmth.c b/crypto/engine/tb_asnmth.c
index 480267daabad91ed1ab65dfc0916d87e1da485c0..980c1277f9e6aa46236f639c8791d4a2f50f37c3 100644 (file)
--- a/crypto/engine/tb_asnmth.c
+++ b/crypto/engine/tb_asnmth.c
@@ -170,7 +170,8 @@ static void look_str_cb(int nid, STACK_OF(ENGINE) *sk, ENGINE *def, void *arg)
         ENGINE *e = sk_ENGINE_value(sk, i);
         EVP_PKEY_ASN1_METHOD *ameth;
         e->pkey_asn1_meths(e, &ameth, NULL, nid);
-        if (((int)strlen(ameth->pem_str) == lk->len)
+        if (ameth != NULL
+                && ((int)strlen(ameth->pem_str) == lk->len)
                 && strncasecmp(ameth->pem_str, lk->str, lk->len) == 0) {
             lk->e = e;
             lk->ameth = ameth;