ksmbd: remove unused compression negotiate ctx packing

build_compression_ctxt() is currently unreachable due to
conn.compress_algorithm remaining zero (SMB3_COMPRESS_NONE).

It appears to have been broken in a couple of subtle ways over the
years:
- prior to d6c9ad23b421 ("ksmbd: use the common definitions for
  NEGOTIATE_PROTOCOL") smb2_compression_ctx.DataLength was set to 8,
  which didn't account for the single CompressionAlgorithms flexible
  array member.
- post d6c9ad23b421 smb2_compression_capabilities_context
  CompressionAlgorithms is a three member array, while
  CompressionAlgorithmCount is set to indicate only one member.
  assemble_neg_contexts() ctxt_size is also incorrectly incremented by
  sizeof(struct smb2_compression_capabilities_context) + 2, which
  assumes one flexible array member.

Signed-off-by: David Disseldorp <[email protected]>
Signed-off-by: Namjae Jeon <[email protected]>

smb2pdu.c

@@ -764,19 +764,6 @@ static void build_encrypt_ctxt(struct smb2_encryption_neg_context *pneg_ctxt,
 	pneg_ctxt->Ciphers[0] = cipher_type;
 }
 
-static void build_compression_ctxt(struct smb2_compression_ctx *pneg_ctxt,
-				   __le16 comp_algo)
-{
-	pneg_ctxt->ContextType = SMB2_COMPRESSION_CAPABILITIES;
-	pneg_ctxt->DataLength =
-		cpu_to_le16(sizeof(struct smb2_compression_ctx)
-			- sizeof(struct smb2_neg_context));
-	pneg_ctxt->Reserved = cpu_to_le32(0);
-	pneg_ctxt->CompressionAlgorithmCount = cpu_to_le16(1);
-	pneg_ctxt->Reserved1 = cpu_to_le32(0);
-	pneg_ctxt->CompressionAlgorithms[0] = comp_algo;
-}
-
 static void build_sign_cap_ctxt(struct smb2_signing_capabilities *pneg_ctxt,
 				__le16 sign_algo)
 {
@@ -840,17 +827,8 @@ static void assemble_neg_contexts(struct ksmbd_conn *conn,
 		ctxt_size += sizeof(struct smb2_encryption_neg_context) + 2;
 	}
 
-	if (conn->compress_algorithm) {
-		ctxt_size = round_up(ctxt_size, 8);
-		ksmbd_debug(SMB,
-			    "assemble SMB2_COMPRESSION_CAPABILITIES context\n");
-		/* Temporarily set to SMB3_COMPRESS_NONE */
-		build_compression_ctxt((struct smb2_compression_ctx *)
-				       (pneg_ctxt + ctxt_size),
-				       conn->compress_algorithm);
-		neg_ctxt_cnt++;
-		ctxt_size += sizeof(struct smb2_compression_ctx) + 2;
-	}
+	/* compression context not yet supported */
+	WARN_ON(conn->compress_algorithm != SMB3_COMPRESS_NONE);
 
 	if (conn->posix_ext_supported) {
 		ctxt_size = round_up(ctxt_size, 8);