Negotiate and save preferred compression algorithms

New negotiate context (3) allows the server and client to
negotiate which compression algorithms to use. Add support
for this and save it off in the server structure.

Also now displayed in /proc/fs/cifs/DebugData (see below example
to Windows 10) where compression algoirthm "LZ77" was negotiated:

Servers:
Number of credits: 326 Dialect 0x311 COMPRESS_LZ77 signed
1) Name: 192.168.92.17 Uses: 1 Capability: 0x300067	Session Status: 1 TCP status: 1 Instance: 1

See MS-XCA and MS-SMB2 2.2.3.1 for more details.
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>

fs/cifs/cifs_debug.c

@@ -332,6 +332,12 @@ static int cifs_debug_data_proc_show(struct seq_file *m, void *v)
 #endif
 		seq_printf(m, "\nNumber of credits: %d Dialect 0x%x",
 			server->credits,  server->dialect);
+		if (server->compress_algorithm == SMB3_COMPRESS_LZNT1)
+			seq_printf(m, " COMPRESS_LZNT1");
+		else if (server->compress_algorithm == SMB3_COMPRESS_LZ77)
+			seq_printf(m, " COMPRESS_LZ77");
+		else if (server->compress_algorithm == SMB3_COMPRESS_LZ77_HUFF)
+			seq_printf(m, " COMPRESS_LZ77_HUFF");
 		if (server->sign)
 			seq_printf(m, " signed");
 		if (server->posix_ext_supported)

fs/cifs/cifsglob.h

@@ -734,6 +734,7 @@ struct TCP_Server_Info {
 #endif /* STATS2 */
 	unsigned int	max_read;
 	unsigned int	max_write;
+	__le16	compress_algorithm;
 	__le16	cipher_type;
 	 /* save initital negprot hash */
 	__u8	preauth_sha_hash[SMB2_PREAUTH_HASH_SIZE];

fs/cifs/smb2pdu.c

@@ -472,6 +472,19 @@ build_preauth_ctxt(struct smb2_preauth_neg_context *pneg_ctxt)
 	pneg_ctxt->HashAlgorithms = SMB2_PREAUTH_INTEGRITY_SHA512;
 }
 
+static void
+build_compression_ctxt(struct smb2_compression_capabilities_context *pneg_ctxt)
+{
+	pneg_ctxt->ContextType = SMB2_COMPRESSION_CAPABILITIES;
+	pneg_ctxt->DataLength =
+		cpu_to_le16(sizeof(struct smb2_compression_capabilities_context)
+			  - sizeof(struct smb2_neg_context));
+	pneg_ctxt->CompressionAlgorithmCount = cpu_to_le16(3);
+	pneg_ctxt->CompressionAlgorithms[0] = SMB3_COMPRESS_LZ77;
+	pneg_ctxt->CompressionAlgorithms[1] = SMB3_COMPRESS_LZ77_HUFF;
+	pneg_ctxt->CompressionAlgorithms[2] = SMB3_COMPRESS_LZNT1;
+}
+
 static void
 build_encrypt_ctxt(struct smb2_encryption_neg_context *pneg_ctxt)
 {
@@ -538,10 +551,17 @@ assemble_neg_contexts(struct smb2_negotiate_req *req,
 	*total_len += ctxt_len;
 	pneg_ctxt += ctxt_len;
 
+	build_compression_ctxt((struct smb2_compression_capabilities_context *)
+				pneg_ctxt);
+	ctxt_len = DIV_ROUND_UP(
+		sizeof(struct smb2_compression_capabilities_context), 8) * 8;
+	*total_len += ctxt_len;
+	pneg_ctxt += ctxt_len;
+
 	build_posix_ctxt((struct smb2_posix_neg_context *)pneg_ctxt);
 	*total_len += sizeof(struct smb2_posix_neg_context);
 
-	req->NegotiateContextCount = cpu_to_le16(3);
+	req->NegotiateContextCount = cpu_to_le16(4);
 }
 
 static void decode_preauth_context(struct smb2_preauth_neg_context *ctxt)
@@ -559,6 +579,27 @@ static void decode_preauth_context(struct smb2_preauth_neg_context *ctxt)
 		printk_once(KERN_WARNING "unknown SMB3 hash algorithm\n");
 }
 
+static void decode_compress_ctx(struct TCP_Server_Info *server,
+			 struct smb2_compression_capabilities_context *ctxt)
+{
+	unsigned int len = le16_to_cpu(ctxt->DataLength);
+
+	/* sizeof compress context is a one element compression capbility struct */
+	if (len < 10) {
+		printk_once(KERN_WARNING "server sent bad compression cntxt\n");
+		return;
+	}
+	if (le16_to_cpu(ctxt->CompressionAlgorithmCount) != 1) {
+		printk_once(KERN_WARNING "illegal SMB3 compress algorithm count\n");
+		return;
+	}
+	if (le16_to_cpu(ctxt->CompressionAlgorithms[0]) > 3) {
+		printk_once(KERN_WARNING "unknown compression algorithm\n");
+		return;
+	}
+	server->compress_algorithm = ctxt->CompressionAlgorithms[0];
+}
+
 static int decode_encrypt_ctx(struct TCP_Server_Info *server,
 			      struct smb2_encryption_neg_context *ctxt)
 {
@@ -623,6 +664,9 @@ static int smb311_decode_neg_context(struct smb2_negotiate_rsp *rsp,
 		else if (pctx->ContextType == SMB2_ENCRYPTION_CAPABILITIES)
 			rc = decode_encrypt_ctx(server,
 				(struct smb2_encryption_neg_context *)pctx);
+		else if (pctx->ContextType == SMB2_COMPRESSION_CAPABILITIES)
+			decode_compress_ctx(server,
+				(struct smb2_compression_capabilities_context *)pctx);
 		else if (pctx->ContextType == SMB2_POSIX_EXTENSIONS_AVAILABLE)
 			server->posix_ext_supported = true;
 		else

fs/cifs/smb2pdu.h

@@ -297,16 +297,19 @@ struct smb2_encryption_neg_context {
 } __packed;
 
 /* See MS-SMB2 2.2.3.1.3 */
-#define SMB3_COMPRESS_NONE	0x0000
-#define SMB3_COMPRESS_LZNT1	0x0001
-#define SMB3_COMPRESS_LZ77	0x0002
-#define SMB3_COMPRESS_LZ77_HUFF	0x0003
+#define SMB3_COMPRESS_NONE	cpu_to_le16(0x0000)
+#define SMB3_COMPRESS_LZNT1	cpu_to_le16(0x0001)
+#define SMB3_COMPRESS_LZ77	cpu_to_le16(0x0002)
+#define SMB3_COMPRESS_LZ77_HUFF	cpu_to_le16(0x0003)
 
 struct smb2_compression_capabilities_context {
+	__le16	ContextType; /* 3 */
+	__le16  DataLength;
+	__u32	Reserved;
 	__le16	CompressionAlgorithmCount;
 	__u16	Padding;
-	__u32	Reserved;
-	__u16	CompressionAlgorithms[1];
+	__u32	Reserved1;
+	__le16	CompressionAlgorithms[3];
 } __packed;
 
 /*