ksmbd: remove unsafe_memcpy use in session setup

commit d782d6e upstream.

Kees pointed out to just use directly ->Buffer instead of pointing
->Buffer using offset not to use unsafe_memcpy().

Suggested-by: Kees Cook <kees@kernel.org>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: namjaejeon

fs/smb/server/smb2pdu.c

@@ -1345,8 +1345,7 @@ static int ntlm_negotiate(struct ksmbd_work *work,
 		return rc;
 
 	sz = le16_to_cpu(rsp->SecurityBufferOffset);
-	chgblob =
-		(struct challenge_message *)((char *)&rsp->hdr.ProtocolId + sz);
+	chgblob = (struct challenge_message *)rsp->Buffer;
 	memset(chgblob, 0, sizeof(struct challenge_message));
 
 	if (!work->conn->use_spnego) {
@@ -1379,9 +1378,7 @@ static int ntlm_negotiate(struct ksmbd_work *work,
 		goto out;
 	}
 
-	sz = le16_to_cpu(rsp->SecurityBufferOffset);
-	unsafe_memcpy((char *)&rsp->hdr.ProtocolId + sz, spnego_blob, spnego_blob_len,
-			/* alloc is larger than blob, see smb2_allocate_rsp_buf() */);
+	memcpy(rsp->Buffer, spnego_blob, spnego_blob_len);
 	rsp->SecurityBufferLength = cpu_to_le16(spnego_blob_len);
 
 out:
@@ -1463,10 +1460,7 @@ static int ntlm_authenticate(struct ksmbd_work *work,
 		if (rc)
 			return -ENOMEM;
 
-		sz = le16_to_cpu(rsp->SecurityBufferOffset);
-		unsafe_memcpy((char *)&rsp->hdr.ProtocolId + sz, spnego_blob,
-				spnego_blob_len,
-				/* alloc is larger than blob, see smb2_allocate_rsp_buf() */);
+		memcpy(rsp->Buffer, spnego_blob, spnego_blob_len);
 		rsp->SecurityBufferLength = cpu_to_le16(spnego_blob_len);
 		kfree(spnego_blob);
 	}