Commit 53d31a3f authored by Steve French's avatar Steve French
Browse files

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: default avatarRonnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: default avatarPavel Shilovsky <pshilovsky@samba.org>
Signed-off-by: default avatarSteve French <stfrench@microsoft.com>
parent e0a3cbcd

fs/cifs/cifsfs.c

+4 −0
Original line number Diff line number Diff line
@@ -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

+3 −0
Original line number Diff line number Diff line
@@ -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

+75 −10
Original line number Diff line number Diff line
@@ -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

+4 −1
Original line number Diff line number Diff line
@@ -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