Fix: tde encrypt buffer context don't use share memory

Now we Fix: tde encrypt buffer context don't use share memory

We did not calculate the size of shared memory for BufEncCtx and BufDecCtx
in the CreateSharedMemoryAndMemories function, which is a potential issue.
There is actually no need to use shared memory here, as the parent process
does not read the values of BufEncCtx and BufDecCtx. When we use AES algorithm
the BufEncCtx and BufDecCtx also does not use shared memory. In order to
maintain a consistent code style,we use malloc. cann't use palloc to apply
for memory here, as TopmemoryContext is NULL during initialization and
the memoryContext has not been setted yet.

Author: kongfanshen

src/backend/crypto/bufenc.c

@@ -36,6 +36,8 @@ static unsigned char buf_encryption_iv[BUFENC_IV_SIZE];
 
 void *BufEncCtx = NULL;
 void *BufDecCtx = NULL;
+static sm4_ctx sm4_enc_ctx;
+static sm4_ctx sm4_dec_ctx;
 
 static void set_buffer_encryption_iv(Page page, BlockNumber blkno);
 
@@ -47,16 +49,28 @@ InitializeBufferEncryption(void)
 	if (!FileEncryptionEnabled)
 		return;
 
+	/* 
+	 * To avoid memory leaks, when the postmaster resets the cluster, 
+	 * need to release the memory which was alloced at last time. 
+	 */
+	if (BufEncCtx && BufEncCtx != &sm4_enc_ctx)
+	{
+		pg_cipher_ctx_free(BufEncCtx);
+		BufEncCtx = NULL;
+	}
+	if (BufDecCtx && BufDecCtx != &sm4_dec_ctx)
+	{
+		pg_cipher_ctx_free(BufDecCtx);
+		BufDecCtx = NULL;
+	}
+	
 	key = KmgrGetKey(KMGR_KEY_ID_REL);
 
 	if (CheckIsSM4Method())
 	{
-		bool found;
-		BufEncCtx = ShmemInitStruct("sm4 encryption method encrypt ctx",
-												sizeof(sm4_ctx), &found);
+		BufEncCtx = &sm4_enc_ctx;
+		BufDecCtx = &sm4_dec_ctx;
 
-		BufDecCtx = ShmemInitStruct("sm4 encryption method decrypt ctx",
-												sizeof(sm4_ctx), &found);
 		sm4_ofb_setkey_enc((sm4_ctx *)BufEncCtx, (unsigned char *)key->key);
 		sm4_ofb_setkey_dec((sm4_ctx *)BufDecCtx, (unsigned char *)key->key);
 	}