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>

1 files changed, 45 insertions, 1 deletions

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 035a568b3dbd..29f011d8d8e2 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -473,6 +473,19 @@ build_preauth_ctxt(struct smb2_preauth_neg_context *pneg_ctxt)
 }
 
 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)
 {
 	pneg_ctxt->ContextType = SMB2_ENCRYPTION_CAPABILITIES;
@@ -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