SMB3.1.1: Add support for negotiating signing algorithm

Support for faster packet signing (using GMAC instead of CMAC) can
now be negotiated to some newer servers, including Windows.
See MS-SMB2 section 2.2.3.17.

This patch adds support for sending the new negotiate context
with the first of three supported signing algorithms (AES-CMAC)
and decoding the response.  A followon patch will add support
for sending the other two (including AES-GMAC, which is fastest)
and changing the signing algorithm used based on what was
negotiated.

To allow the client to request GMAC signing set module parameter
"enable_negotiate_signing" to 1.
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Pavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifsfs.c

@@ -65,6 +65,7 @@ bool lookupCacheEnabled = true;
 bool disable_legacy_dialects; /* false by default */
 bool enable_gcm_256 = true;
 bool require_gcm_256; /* false by default */
+bool enable_negotiate_signing; /* false by default */
 unsigned int global_secflags = CIFSSEC_DEF;
 /* unsigned int ntlmv2_support = 0; */
 unsigned int sign_CIFS_PDUs = 1;
@@ -104,6 +105,9 @@ MODULE_PARM_DESC(enable_gcm_256, "Enable requesting strongest (256 bit) GCM encr
 module_param(require_gcm_256, bool, 0644);
 MODULE_PARM_DESC(require_gcm_256, "Require strongest (256 bit) GCM encryption. Default: n/N/0");
 
+module_param(enable_negotiate_signing, bool, 0644);
+MODULE_PARM_DESC(enable_negotiate_signing, "Enable negotiating packet signing algorithm with server. Default: n/N/0");
+
 module_param(disable_legacy_dialects, bool, 0644);
 MODULE_PARM_DESC(disable_legacy_dialects, "To improve security it may be "
 				  "helpful to restrict the ability to "

fs/cifs/cifsglob.h

@@ -667,9 +667,11 @@ struct TCP_Server_Info {
 	unsigned int	max_write;
 	unsigned int	min_offload;
 	__le16	compress_algorithm;
+	__u16	signing_algorithm;
 	__le16	cipher_type;
 	 /* save initital negprot hash */
 	__u8	preauth_sha_hash[SMB2_PREAUTH_HASH_SIZE];
+	bool	signing_negotiated; /* true if valid signing context rcvd from server */
 	bool	posix_ext_supported;
 	struct delayed_work reconnect; /* reconnect workqueue job */
 	struct mutex reconnect_mutex; /* prevent simultaneous reconnects */
@@ -1869,6 +1871,7 @@ extern unsigned int global_secflags;	/* if on, session setup sent
 extern unsigned int sign_CIFS_PDUs;  /* enable smb packet signing */
 extern bool enable_gcm_256; /* allow optional negotiate of strongest signing (aes-gcm-256) */
 extern bool require_gcm_256; /* require use of strongest signing (aes-gcm-256) */
+extern bool enable_negotiate_signing; /* request use of faster (GMAC) signing if available */
 extern bool linuxExtEnabled;/*enable Linux/Unix CIFS extensions*/
 extern unsigned int CIFSMaxBufSize;  /* max size not including hdr */
 extern unsigned int cifs_min_rcv;    /* min size of big ntwrk buf pool */

fs/cifs/smb2pdu.c

@@ -433,6 +433,29 @@ build_compression_ctxt(struct smb2_compression_capabilities_context *pneg_ctxt)
 	pneg_ctxt->CompressionAlgorithms[2] = SMB3_COMPRESS_LZNT1;
 }
 
+static unsigned int
+build_signing_ctxt(struct smb2_signing_capabilities *pneg_ctxt)
+{
+	unsigned int ctxt_len = sizeof(struct smb2_signing_capabilities);
+	unsigned short num_algs = 1; /* number of signing algorithms sent */
+
+	pneg_ctxt->ContextType = SMB2_SIGNING_CAPABILITIES;
+	/*
+	 * Context Data length must be rounded to multiple of 8 for some servers
+	 */
+	pneg_ctxt->DataLength = cpu_to_le16(DIV_ROUND_UP(
+				sizeof(struct smb2_signing_capabilities) -
+				sizeof(struct smb2_neg_context) +
+				(num_algs * 2 /* sizeof u16 */), 8) * 8);
+	pneg_ctxt->SigningAlgorithmCount = cpu_to_le16(num_algs);
+	pneg_ctxt->SigningAlgorithms[0] = cpu_to_le16(SIGNING_ALG_AES_CMAC);
+
+	ctxt_len += 2 /* sizeof le16 */ * num_algs;
+	ctxt_len = DIV_ROUND_UP(ctxt_len, 8) * 8;
+	return ctxt_len;
+	/* TBD add SIGNING_ALG_AES_GMAC and/or SIGNING_ALG_HMAC_SHA256 */
+}
+
 static void
 build_encrypt_ctxt(struct smb2_encryption_neg_context *pneg_ctxt)
 {
@@ -498,7 +521,7 @@ assemble_neg_contexts(struct smb2_negotiate_req *req,
 		      struct TCP_Server_Info *server, unsigned int *total_len)
 {
 	char *pneg_ctxt;
-	unsigned int ctxt_len;
+	unsigned int ctxt_len, neg_context_count;
 
 	if (*total_len > 200) {
 		/* In case length corrupted don't want to overrun smb buffer */
@@ -525,6 +548,17 @@ assemble_neg_contexts(struct smb2_negotiate_req *req,
 	*total_len += ctxt_len;
 	pneg_ctxt += ctxt_len;
 
+	ctxt_len = build_netname_ctxt((struct smb2_netname_neg_context *)pneg_ctxt,
+					server->hostname);
+	*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);
+	pneg_ctxt += sizeof(struct smb2_posix_neg_context);
+
+	neg_context_count = 4;
+
 	if (server->compress_algorithm) {
 		build_compression_ctxt((struct smb2_compression_capabilities_context *)
 				pneg_ctxt);
@@ -533,17 +567,20 @@ assemble_neg_contexts(struct smb2_negotiate_req *req,
 				8) * 8;
 		*total_len += ctxt_len;
 		pneg_ctxt += ctxt_len;
-		req->NegotiateContextCount = cpu_to_le16(5);
-	} else
-		req->NegotiateContextCount = cpu_to_le16(4);
+		neg_context_count++;
+	}
 
-	ctxt_len = build_netname_ctxt((struct smb2_netname_neg_context *)pneg_ctxt,
-					server->hostname);
+	if (enable_negotiate_signing) {
+		ctxt_len = build_signing_ctxt((struct smb2_signing_capabilities *)
+				pneg_ctxt);
 		*total_len += ctxt_len;
 		pneg_ctxt += ctxt_len;
+		neg_context_count++;
+	}
+
+	/* check for and add transport_capabilities and signing capabilities */
+	req->NegotiateContextCount = cpu_to_le16(neg_context_count);
 
-	build_posix_ctxt((struct smb2_posix_neg_context *)pneg_ctxt);
-	*total_len += sizeof(struct smb2_posix_neg_context);
 }
 
 static void decode_preauth_context(struct smb2_preauth_neg_context *ctxt)
@@ -632,6 +669,31 @@ static int decode_encrypt_ctx(struct TCP_Server_Info *server,
 	return 0;
 }
 
+static void decode_signing_ctx(struct TCP_Server_Info *server,
+			       struct smb2_signing_capabilities *pctxt)
+{
+	unsigned int len = le16_to_cpu(pctxt->DataLength);
+
+	if ((len < 4) || (len > 16)) {
+		pr_warn_once("server sent bad signing negcontext\n");
+		return;
+	}
+	if (le16_to_cpu(pctxt->SigningAlgorithmCount) != 1) {
+		pr_warn_once("Invalid signing algorithm count\n");
+		return;
+	}
+	if (le16_to_cpu(pctxt->SigningAlgorithms[0]) > 2) {
+		pr_warn_once("unknown signing algorithm\n");
+		return;
+	}
+
+	server->signing_negotiated = true;
+	server->signing_algorithm = le16_to_cpu(pctxt->SigningAlgorithms[0]);
+	cifs_dbg(FYI, "signing algorithm %d chosen\n",
+		     server->signing_algorithm);
+}
+
+
 static int smb311_decode_neg_context(struct smb2_negotiate_rsp *rsp,
 				     struct TCP_Server_Info *server,
 				     unsigned int len_of_smb)
@@ -675,6 +737,9 @@ static int smb311_decode_neg_context(struct smb2_negotiate_rsp *rsp,
 				(struct smb2_compression_capabilities_context *)pctx);
 		else if (pctx->ContextType == SMB2_POSIX_EXTENSIONS_AVAILABLE)
 			server->posix_ext_supported = true;
+		else if (pctx->ContextType == SMB2_SIGNING_CAPABILITIES)
+			decode_signing_ctx(server,
+				(struct smb2_signing_capabilities *)pctx);
 		else
 			cifs_server_dbg(VFS, "unknown negcontext of type %d ignored\n",
 				le16_to_cpu(pctx->ContextType));

fs/cifs/smb2pdu.h

@@ -329,7 +329,7 @@ struct smb2_neg_context {
 	__le16	ContextType;
 	__le16	DataLength;
 	__le32	Reserved;
-	/* Followed by array of data */
+	/* Followed by array of data. NOTE: some servers require padding to 8 byte boundary */
 } __packed;
 
 #define SMB311_LINUX_CLIENT_SALT_SIZE			32
@@ -394,6 +394,7 @@ struct smb2_compression_capabilities_context {
 	__u16	Padding;
 	__u32	Flags;
 	__le16	CompressionAlgorithms[3];
+	/* Check if pad needed */
 } __packed;
 
 /*
@@ -420,6 +421,7 @@ struct smb2_transport_capabilities_context {
 	__le16  DataLength;
 	__u32	Reserved;
 	__le32	Flags;
+	__u32	Pad;
 } __packed;
 
 /*
@@ -458,6 +460,7 @@ struct smb2_signing_capabilities {
 	__u32	Reserved;
 	__le16	SigningAlgorithmCount;
 	__le16	SigningAlgorithms[];
+	/*  Followed by padding to 8 byte boundary (required by some servers) */
 } __packed;
 
 #define POSIX_CTXT_DATA_LEN	16