s3:libsmb: add a much simplified smb_siging infrastructure

It's the job of the caller to maintain the seqnum/mid mapping.

Hopefully we can use this code in s4 later too.

metze

1 files changed, 370 insertions, 0 deletions

diff --git a/source3/libsmb/smb_signing.c b/source3/libsmb/smb_signing.c
new file mode 100644
index 0000000000..32d2883965
--- /dev/null
+++ b/source3/libsmb/smb_signing.c
@@ -0,0 +1,370 @@
+/*
+   Unix SMB/CIFS implementation.
+   SMB Signing Code
+   Copyright (C) Jeremy Allison 2003.
+   Copyright (C) Andrew Bartlett <abartlet@samba.org> 2002-2003
+   Copyright (C) Stefan Metzmacher 2009
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "includes.h"
+
+/* Used by the SMB signing functions. */
+
+struct smb_signing_state {
+	/* is signing localy allowed */
+	bool allowed;
+
+	/* is signing localy mandatory */
+	bool mandatory;
+
+	/* is signing negotiated by the peer */
+	bool negotiated;
+
+	/* send BSRSPYL signatures */
+	bool bsrspyl;
+
+	bool active; /* Have I ever seen a validly signed packet? */
+
+	/* mac_key.length > 0 means signing is started */
+	DATA_BLOB mac_key;
+
+	/* the next expected seqnum */
+	uint32_t seqnum;
+};
+
+static void smb_signing_reset_info(struct smb_signing_state *si)
+{
+	si->active = false;
+	si->bsrspyl = false;
+	data_blob_free(&si->mac_key);
+	si->seqnum = 0;
+}
+
+struct smb_signing_state *smb_signing_init(TALLOC_CTX *mem_ctx,
+					   bool allowed,
+					   bool mandatory)
+{
+	struct smb_signing_state *si;
+
+	si = talloc_zero(mem_ctx, struct smb_signing_state);
+	if (si == NULL) {
+		return NULL;
+	}
+
+	if (mandatory) {
+		allowed = true;
+	}
+
+	si->allowed = allowed;
+	si->mandatory = mandatory;
+
+	return si;
+}
+
+static bool smb_signing_good(struct smb_signing_state *si,
+			     bool good, uint32_t seq)
+{
+	if (good) {
+		if (!si->active) {
+			si->active = true;
+		}
+		return true;
+	}
+
+	if (!si->mandatory && !si->active) {
+		/* Non-mandatory signing - just turn off if this is the first bad packet.. */
+		DEBUG(5, ("smb_signing_good: signing negotiated but not required and peer\n"
+			  "isn't sending correct signatures. Turning off.\n"));
+		smb_signing_reset_info(si);
+		return true;
+	}
+
+	/* Mandatory signing or bad packet after signing started - fail and disconnect. */
+	DEBUG(0, ("smb_signing_good: BAD SIG: seq %u\n", (unsigned int)seq));
+	return false;
+}
+
+static void smb_signing_md5(const DATA_BLOB *mac_key,
+			    const uint8_t *buf, uint32_t seq_number,
+			    uint8_t calc_md5_mac[16])
+{
+	const size_t offset_end_of_sig = (smb_ss_field + 8);
+	uint8_t sequence_buf[8];
+	struct MD5Context md5_ctx;
+
+	/*
+	 * Firstly put the sequence number into the first 4 bytes.
+	 * and zero out the next 4 bytes.
+	 *
+	 * We do this here, to avoid modifying the packet.
+	 */
+
+	DEBUG(10,("smb_signing_md5: sequence number %u\n", seq_number ));
+
+	SIVAL(sequence_buf, 0, seq_number);
+	SIVAL(sequence_buf, 4, 0);
+
+	/* Calculate the 16 byte MAC - but don't alter the data in the
+	   incoming packet.
+
+	   This makes for a bit of fussing about, but it's not too bad.
+	*/
+	MD5Init(&md5_ctx);
+
+	/* intialise with the key */
+	MD5Update(&md5_ctx, mac_key->data, mac_key->length);
+
+	/* copy in the first bit of the SMB header */
+	MD5Update(&md5_ctx, buf + 4, smb_ss_field - 4);
+
+	/* copy in the sequence number, instead of the signature */
+	MD5Update(&md5_ctx, sequence_buf, sizeof(sequence_buf));
+
+	/* copy in the rest of the packet in, skipping the signature */
+	MD5Update(&md5_ctx, buf + offset_end_of_sig, 
+		  smb_len(buf) - (offset_end_of_sig - 4));
+
+	/* calculate the MD5 sig */
+	MD5Final(calc_md5_mac, &md5_ctx);
+}
+
+uint32_t smb_signing_next_seqnum(struct smb_signing_state *si, bool oneway)
+{
+	uint32_t seqnum;
+
+	if (si->mac_key.length == 0) {
+		return 0;
+	}
+
+	seqnum = si->seqnum;
+	if (oneway) {
+		si->seqnum += 1;
+	} else {
+		si->seqnum += 2;
+	}
+
+	return seqnum;
+}
+
+void smb_signing_cancel_reply(struct smb_signing_state *si, bool oneway)
+{
+	if (si->mac_key.length == 0) {
+		return;
+	}
+
+	if (oneway) {
+		si->seqnum -= 1;
+	} else {
+		si->seqnum -= 2;
+	}
+}
+
+void smb_signing_sign_pdu(struct smb_signing_state *si,
+			  uint8_t *outbuf, uint32_t seqnum)
+{
+	uint8_t calc_md5_mac[16];
+	uint16_t flags2;
+
+	if (si->mac_key.length == 0) {
+		if (!si->bsrspyl) {
+			return;
+		}
+	}
+
+	/* JRA Paranioa test - we should be able to get rid of this... */
+	if (smb_len(outbuf) < (smb_ss_field + 8 - 4)) {
+		DEBUG(1,("smb_signing_sign_pdu: Logic error. "
+			 "Can't check signature on short packet! smb_len = %u\n",
+			 smb_len(outbuf)));
+		abort();
+	}
+
+	/* mark the packet as signed - BEFORE we sign it...*/
+	flags2 = SVAL(outbuf,smb_flg2);
+	flags2 |= FLAGS2_SMB_SECURITY_SIGNATURES;
+	SSVAL(outbuf, smb_flg2, flags2);
+
+	if (si->bsrspyl) {
+		/* I wonder what BSRSPYL stands for - but this is what MS
+		   actually sends! */
+		memcpy(calc_md5_mac, "BSRSPYL ", 8);
+	} else {
+		smb_signing_md5(&si->mac_key, outbuf,
+				seqnum, calc_md5_mac);
+	}
+
+	DEBUG(10, ("smb_signing_sign_pdu: sent SMB signature of\n"));
+	dump_data(10, calc_md5_mac, 8);
+
+	memcpy(&outbuf[smb_ss_field], calc_md5_mac, 8);
+
+/*	outbuf[smb_ss_field+2]=0;
+	Uncomment this to test if the remote server actually verifies signatures...*/
+}
+
+bool smb_signing_check_pdu(struct smb_signing_state *si,
+			   const uint8_t *inbuf, uint32_t seqnum)
+{
+	bool good;
+	uint8_t calc_md5_mac[16];
+	const uint8_t *reply_sent_mac;
+
+	if (si->mac_key.length == 0) {
+		return true;
+	}
+
+	if (smb_len(inbuf) < (smb_ss_field + 8 - 4)) {
+		DEBUG(1,("smb_signing_check_pdu: Can't check signature "
+			 "on short packet! smb_len = %u\n",
+			 smb_len(inbuf)));
+		return False;
+	}
+
+	smb_signing_md5(&si->mac_key, inbuf,
+			seqnum, calc_md5_mac);
+
+	reply_sent_mac = &inbuf[smb_ss_field];
+	good = (memcmp(reply_sent_mac, calc_md5_mac, 8) == 0);
+
+	if (!good) {
+		int i;
+		const int sign_range = 5;
+
+		DEBUG(5, ("smb_signing_check_pdu: BAD SIG: wanted SMB signature of\n"));
+		dump_data(5, calc_md5_mac, 8);
+
+		DEBUG(5, ("smb_signing_check_pdu: BAD SIG: got SMB signature of\n"));
+		dump_data(5, reply_sent_mac, 8);
+
+		for (i = -sign_range; i < sign_range; i++) {
+			smb_signing_md5(&si->mac_key, inbuf,
+					seqnum+i, calc_md5_mac);
+			if (memcmp(reply_sent_mac, calc_md5_mac, 8) == 0) {
+				DEBUG(0,("smb_signing_check_pdu: "
+					 "out of seq. seq num %u matches. "
+					 "We were expecting seq %u\n",
+					 (unsigned int)seqnum+i,
+					 (unsigned int)seqnum));
+				break;
+			}
+		}
+	} else {
+		DEBUG(10, ("smb_signing_check_pdu: seq %u: "
+			   "got good SMB signature of\n",
+			   (unsigned int)seqnum));
+		dump_data(10, reply_sent_mac, 8);
+	}
+
+	return smb_signing_good(si, good, seqnum);
+}
+
+bool smb_signing_set_bsrspyl(struct smb_signing_state *si)
+{
+	if (!si->negotiated) {
+		return false;
+	}
+
+	if (si->active) {
+		return false;
+	}
+
+	si->bsrspyl = true;
+
+	return true;
+}
+
+bool smb_signing_activate(struct smb_signing_state *si,
+			  const DATA_BLOB user_session_key,
+			  const DATA_BLOB response)
+{
+	size_t len;
+	off_t ofs;
+
+	if (!user_session_key.length) {
+		return false;
+	}
+
+	if (!si->negotiated) {
+		return false;
+	}
+
+	if (si->active) {
+		return false;
+	}
+
+	if (si->mac_key.length > 0) {
+		return false;
+	}
+
+	smb_signing_reset_info(si);
+
+	len = response.length + user_session_key.length;
+	si->mac_key = data_blob_talloc(si, NULL, len);
+
+	ofs = 0;
+	memcpy(&si->mac_key.data[ofs], user_session_key.data, user_session_key.length);
+
+	DEBUG(10, ("smb_signing_activate: user_session_key\n"));
+	dump_data(10, user_session_key.data, user_session_key.length);
+
+	if (response.length) {
+		ofs = user_session_key.length;
+		memcpy(&si->mac_key.data[ofs], response.data, response.length);
+		DEBUG(10, ("smb_signing_activate: response_data\n"));
+		dump_data(10, response.data, response.length);
+	} else {
+		DEBUG(10, ("smb_signing_activate: NULL response_data\n"));
+	}
+
+	dump_data_pw("smb_signing_activate: mac key is:\n",
+		     si->mac_key.data, si->mac_key.length);
+
+	/* Initialise the sequence number */
+	si->seqnum = 2;
+
+	return true;
+}
+
+bool smb_signing_is_active(struct smb_signing_state *si)
+{
+	return si->active;
+}
+
+bool smb_signing_is_allowed(struct smb_signing_state *si)
+{
+	return si->allowed;
+}
+
+bool smb_signing_is_mandatory(struct smb_signing_state *si)
+{
+	return si->mandatory;
+}
+
+bool smb_signing_set_negotiated(struct smb_signing_state *si)
+{
+	if (!si->allowed) {
+		return false;
+	}
+
+	si->negotiated = true;
+
+	return true;
+}
+
+bool smb_signing_is_negotiated(struct smb_signing_state *si)
+{
+	return si->negotiated;
+}