ksmbd: avoid duplicate negotiate ctx offset increments

Both pneg_ctxt and ctxt_size change in unison, with each adding the
length of the previously added context, rounded up to an eight byte
boundary.
Drop pneg_ctxt increments and instead use the ctxt_size offset when
passing output pointers to per-context helper functions. This slightly
simplifies offset tracking and shaves off a few text bytes.
Before (x86-64 gcc 7.5):
   text    data     bss     dec     hex filename
 213234    8677     672  222583   36577 ksmbd.ko

After:
   text    data     bss     dec     hex filename
 213218    8677     672  222567   36567 ksmbd.ko

Signed-off-by: David Disseldorp <ddiss@suse.de>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/ksmbd/smb2pdu.c

@@ -808,7 +808,7 @@ static void assemble_neg_contexts(struct ksmbd_conn *conn,
 				  struct smb2_negotiate_rsp *rsp,
 				  void *smb2_buf_len)
 {
-	char *pneg_ctxt = (char *)rsp +
+	char * const pneg_ctxt = (char *)rsp +
 			le32_to_cpu(rsp->NegotiateContextOffset);
 	int neg_ctxt_cnt = 1;
 	int ctxt_size;
@@ -819,53 +819,47 @@ static void assemble_neg_contexts(struct ksmbd_conn *conn,
 			   conn->preauth_info->Preauth_HashId);
 	inc_rfc1001_len(smb2_buf_len, AUTH_GSS_PADDING);
 	ctxt_size = sizeof(struct smb2_preauth_neg_context);
-	/* Round to 8 byte boundary */
-	pneg_ctxt += round_up(sizeof(struct smb2_preauth_neg_context), 8);
 
 	if (conn->cipher_type) {
+		/* Round to 8 byte boundary */
 		ctxt_size = round_up(ctxt_size, 8);
 		ksmbd_debug(SMB,
 			    "assemble SMB2_ENCRYPTION_CAPABILITIES context\n");
-		build_encrypt_ctxt((struct smb2_encryption_neg_context *)pneg_ctxt,
+		build_encrypt_ctxt((struct smb2_encryption_neg_context *)
+				   (pneg_ctxt + ctxt_size),
 				   conn->cipher_type);
 		neg_ctxt_cnt++;
 		ctxt_size += sizeof(struct smb2_encryption_neg_context) + 2;
-		/* Round to 8 byte boundary */
-		pneg_ctxt +=
-			round_up(sizeof(struct smb2_encryption_neg_context) + 2,
-				 8);
 	}
 
 	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_capabilities_context *)pneg_ctxt,
+		build_compression_ctxt((struct smb2_compression_capabilities_context *)
+				       (pneg_ctxt + ctxt_size),
 				       conn->compress_algorithm);
 		neg_ctxt_cnt++;
 		ctxt_size += sizeof(struct smb2_compression_capabilities_context) + 2;
-		/* Round to 8 byte boundary */
-		pneg_ctxt += round_up(sizeof(struct smb2_compression_capabilities_context) + 2,
-				      8);
 	}
 
 	if (conn->posix_ext_supported) {
 		ctxt_size = round_up(ctxt_size, 8);
 		ksmbd_debug(SMB,
 			    "assemble SMB2_POSIX_EXTENSIONS_AVAILABLE context\n");
-		build_posix_ctxt((struct smb2_posix_neg_context *)pneg_ctxt);
+		build_posix_ctxt((struct smb2_posix_neg_context *)
+				 (pneg_ctxt + ctxt_size));
 		neg_ctxt_cnt++;
 		ctxt_size += sizeof(struct smb2_posix_neg_context);
-		/* Round to 8 byte boundary */
-		pneg_ctxt += round_up(sizeof(struct smb2_posix_neg_context), 8);
 	}
 
 	if (conn->signing_negotiated) {
 		ctxt_size = round_up(ctxt_size, 8);
 		ksmbd_debug(SMB,
 			    "assemble SMB2_SIGNING_CAPABILITIES context\n");
-		build_sign_cap_ctxt((struct smb2_signing_capabilities *)pneg_ctxt,
+		build_sign_cap_ctxt((struct smb2_signing_capabilities *)
+				    (pneg_ctxt + ctxt_size),
 				    conn->signing_algorithm);
 		neg_ctxt_cnt++;
 		ctxt_size += sizeof(struct smb2_signing_capabilities) + 2;