From 4c27f85b79e853bf28e774638b4225dbc1defc4c Mon Sep 17 00:00:00 2001
From: Steve French <stfrench@microsoft.com>
Date: Sun, 27 Jun 2021 15:30:24 -0500
Subject: [PATCH] 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
and decoding the response.  A followon patch will add support
for changing the signing algorithm used based on what was
negotiated.

To allow the client to request GMAC signing set module parameter
"enable_GMAC_signing" to 1.

Signed-off-by: Steve French <stfrench@microsoft.com>
---
 fs/cifs/cifsfs.c   |  4 +++
 fs/cifs/cifsglob.h |  2 ++
 fs/cifs/smb2pdu.c  | 77 ++++++++++++++++++++++++++++++++++++++++------
 fs/cifs/smb2pdu.h  |  5 ++-
 4 files changed, 77 insertions(+), 11 deletions(-)

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index 9fb874dd8d24..280d0952f912 100644
--- a/fs/cifs/cifsfs.c
+++ b/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_GMAC_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_GMAC_signing, bool, 0644);
+MODULE_PARM_DESC(enable_GMAC_signing, "Enable requesting faster (GMAC) packet signing. 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 "
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 3100f8b66e60..ac2e98e1ba60 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -666,6 +666,7 @@ struct TCP_Server_Info {
 	unsigned int	max_write;
 	unsigned int	min_offload;
 	__le16	compress_algorithm;
+	__le16	signing_algorithm;
 	__le16	cipher_type;
 	 /* save initital negprot hash */
 	__u8	preauth_sha_hash[SMB2_PREAUTH_HASH_SIZE];
@@ -1868,6 +1869,7 @@ 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_GMAC_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 */
diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 962826dc3316..e8359b9f72d2 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -433,6 +433,18 @@ build_compression_ctxt(struct smb2_compression_capabilities_context *pneg_ctxt)
 	pneg_ctxt->CompressionAlgorithms[2] = SMB3_COMPRESS_LZNT1;
 }
 
+static void
+build_signing_ctxt(struct smb2_signing_capabilities *pneg_ctxt)
+{
+	pneg_ctxt->ContextType = SMB2_SIGNING_CAPABILITIES;
+	pneg_ctxt->DataLength =
+		cpu_to_le16(sizeof(struct smb2_signing_capabilities)
+			  - sizeof(struct smb2_neg_context));
+	pneg_ctxt->SigningAlgorithmCount = cpu_to_le16(2);
+	pneg_ctxt->SigningAlgorithms[0] = cpu_to_le16(SIGNING_ALG_AES_CMAC);
+	pneg_ctxt->SigningAlgorithms[1] = cpu_to_le16(SIGNING_ALG_AES_GMAC);
+}
+
 static void
 build_encrypt_ctxt(struct smb2_encryption_neg_context *pneg_ctxt)
 {
@@ -498,7 +510,7 @@ 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 +537,17 @@ 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 +556,24 @@ 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);
-	*total_len += ctxt_len;
-	pneg_ctxt += ctxt_len;
+	if (enable_GMAC_signing) {
+		pr_warn_once("requesting GMAC signing is experimental\n");
+		build_signing_ctxt((struct smb2_signing_capabilities *)
+				pneg_ctxt);
+		ctxt_len = DIV_ROUND_UP(
+			sizeof(struct smb2_signing_capabilities),
+				8) * 8;
+		*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 +662,30 @@ 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_algorithm = pctxt->SigningAlgorithms[0];
+
+	cifs_dbg(VFS, "GMAC signing is experimental.  Algorithm %d chosen\n",
+		     le16_to_cpu(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 +729,9 @@ 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));
diff --git a/fs/cifs/smb2pdu.h b/fs/cifs/smb2pdu.h
index a5c48b85549a..67d701783182 100644
--- a/fs/cifs/smb2pdu.h
+++ b/fs/cifs/smb2pdu.h
@@ -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;
 
 /*
@@ -457,7 +459,8 @@ struct smb2_signing_capabilities {
 	__le16	DataLength;
 	__u32	Reserved;
 	__le16	SigningAlgorithmCount;
-	__le16	SigningAlgorithms[];
+	__le16	SigningAlgorithms[2];  /* CMAC and GMAC */
+	__u16	Pad;  /* Pad to 8 byte rounding */
 } __packed;
 
 #define POSIX_CTXT_DATA_LEN	16
-- 
2.30.2

