Introduce EVP_MD_CTX_set_pkey_ctx

Thus users can use this function to set customized EVP_PKEY_CTX to
EVP_MD_CTX structure.
Reviewed-by: NTim Hudson <tjh@openssl.org>
Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7113)

crypto/evp/digest.c

@@ -32,7 +32,12 @@ int EVP_MD_CTX_reset(EVP_MD_CTX *ctx)
         && !EVP_MD_CTX_test_flags(ctx, EVP_MD_CTX_FLAG_REUSE)) {
         OPENSSL_clear_free(ctx->md_data, ctx->digest->ctx_size);
     }
-    EVP_PKEY_CTX_free(ctx->pctx);
+    /*
+     * pctx should be freed by the user of EVP_MD_CTX
+     * if EVP_MD_CTX_FLAG_NEGLECT_PCTX is set
+     */
+    if (!EVP_MD_CTX_test_flags(ctx, EVP_MD_CTX_FLAG_NEGLECT_PCTX))
+        EVP_PKEY_CTX_free(ctx->pctx);
 #ifndef OPENSSL_NO_ENGINE
     ENGINE_finish(ctx->engine);
 #endif

crypto/evp/evp_lib.c

@@ -460,6 +460,13 @@ EVP_PKEY_CTX *EVP_MD_CTX_pkey_ctx(const EVP_MD_CTX *ctx)
     return ctx->pctx;
 }
 
+void EVP_MD_CTX_set_pkey_ctx(EVP_MD_CTX *ctx, EVP_PKEY_CTX *pctx)
+{
+    ctx->pctx = pctx;
+    /* make sure pctx is not freed when destroying EVP_MD_CTX */
+    EVP_MD_CTX_set_flags(ctx, EVP_MD_CTX_FLAG_NEGLECT_PCTX);
+}
+
 void *EVP_MD_CTX_md_data(const EVP_MD_CTX *ctx)
 {
     return ctx->md_data;

include/openssl/evp.h

@@ -181,6 +181,9 @@ int (*EVP_MD_meth_get_ctrl(const EVP_MD *md))(EVP_MD_CTX *ctx, int cmd,
  */
 # define EVP_MD_CTX_FLAG_FINALISE        0x0200
 
+/* Don't free up ctx->pctx in EVP_MD_CTX_reset */
+# define EVP_MD_CTX_FLAG_NEGLECT_PCTX    0x0400
+
 EVP_CIPHER *EVP_CIPHER_meth_new(int cipher_type, int block_size, int key_len);
 EVP_CIPHER *EVP_CIPHER_meth_dup(const EVP_CIPHER *cipher);
 void EVP_CIPHER_meth_free(EVP_CIPHER *cipher);
@@ -453,6 +456,7 @@ void EVP_MD_CTX_set_update_fn(EVP_MD_CTX *ctx,
 # define EVP_MD_CTX_block_size(e)        EVP_MD_block_size(EVP_MD_CTX_md(e))
 # define EVP_MD_CTX_type(e)              EVP_MD_type(EVP_MD_CTX_md(e))
 EVP_PKEY_CTX *EVP_MD_CTX_pkey_ctx(const EVP_MD_CTX *ctx);
+void EVP_MD_CTX_set_pkey_ctx(EVP_MD_CTX *ctx, EVP_PKEY_CTX *pctx);
 void *EVP_MD_CTX_md_data(const EVP_MD_CTX *ctx);
 
 int EVP_CIPHER_nid(const EVP_CIPHER *cipher);

util/libcrypto.num

@@ -4574,3 +4574,4 @@ EC_GROUP_set_curve                      4527	1_1_1	EXIST::FUNCTION:EC
 EC_GROUP_get_curve                      4528	1_1_1	EXIST::FUNCTION:EC
 OCSP_resp_get0_tbs_sigalg               4529	1_1_0j	EXIST::FUNCTION:OCSP
 OCSP_resp_get0_respdata                 4530	1_1_0j	EXIST::FUNCTION:OCSP
+EVP_MD_CTX_set_pkey_ctx                 4531	1_1_1	EXIST::FUNCTION: