"Reserve" the method store when constructing methods

Introducing the concept of reserving the store where a number of
provided operation methods are to be stored.

This avoids racing when constructing provided methods, which is
especially pertinent when multiple threads are trying to fetch the
same method, or even any implementation for the same given operation
type.

This introduces a |biglock| in OSSL_METHOD_STORE, which is separate
from the |lock| which is used for more internal and finer grained
locking.

Fixes #18152

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18153)

1 files changed, 24 insertions, 0 deletions

diff --git a/crypto/evp/evp_fetch.c b/crypto/evp/evp_fetch.c
index 9af92bd412..4908f6cfee 100644
--- a/crypto/evp/evp_fetch.c
+++ b/crypto/evp/evp_fetch.c
@@ -63,6 +63,28 @@ static OSSL_METHOD_STORE *get_evp_method_store(OSSL_LIB_CTX *libctx)
     return ossl_lib_ctx_get_data(libctx, OSSL_LIB_CTX_EVP_METHOD_STORE_INDEX);
 }
 
+static int reserve_evp_method_store(void *store, void *data)
+{
+    struct evp_method_data_st *methdata = data;
+
+    if (store == NULL
+        && (store = get_evp_method_store(methdata->libctx)) == NULL)
+        return 0;
+
+    return ossl_method_lock_store(store);
+}
+
+static int unreserve_evp_method_store(void *store, void *data)
+{
+    struct evp_method_data_st *methdata = data;
+
+    if (store == NULL
+        && (store = get_evp_method_store(methdata->libctx)) == NULL)
+        return 0;
+
+    return ossl_method_unlock_store(store);
+}
+
 /*
  * To identify the method in the EVP method store, we mix the name identity
  * with the operation identity, under the assumption that we don't have more
@@ -271,6 +293,8 @@ inner_evp_generic_fetch(struct evp_method_data_st *methdata,
         || !ossl_method_store_cache_get(store, prov, meth_id, propq, &method)) {
         OSSL_METHOD_CONSTRUCT_METHOD mcm = {
             get_tmp_evp_method_store,
+            reserve_evp_method_store,
+            unreserve_evp_method_store,
             get_evp_method_from_store,
             put_evp_method_in_store,
             construct_evp_method,