detect: add tcp.wscale keyword

Allows matching on wscale option value in TCP header options.

Ticket: #7713.

doc/userguide/rules/header-keywords.rst

@@ -454,6 +454,26 @@ Example rule:
 
     alert tcp $EXTERNAL_NET any -> $HOME_NET any (flow:stateless; flags:S,12; :example-rule-emphasis:`tcp.mss:<536;` sid:1234; rev:5;)
 
+tcp.wscale
+^^^^^^^^^^
+
+Match on the TCP window scaling option value. Will not match if the option is not
+present.
+
+``tcp.wscale`` uses an :ref:`unsigned 8-bit integer <rules-integer-keywords>`.
+
+The format of the keyword is::
+
+  tcp.wscale:<min>-<max>;
+  tcp.wscale:[<|>]<number>;
+  tcp.wscale:<value>;
+
+Example rule:
+
+.. container:: example-rule
+
+    alert tcp $EXTERNAL_NET any -> $HOME_NET any (flow:stateless; flags:S,12; :example-rule-emphasis:`tcp.wscale:>10;` sid:1234; rev:5;)
+
 tcp.hdr
 ^^^^^^^
 

src/Makefile.am

@@ -299,6 +299,7 @@ noinst_HEADERS = \
 	detect-tcp-flags.h \
 	detect-tcp-seq.h \
 	detect-tcp-window.h \
+	detect-tcp-wscale.h \
 	detect-tcphdr.h \
 	detect-tcpmss.h \
 	detect-template.h \
@@ -896,6 +897,7 @@ libsuricata_c_a_SOURCES = \
 	detect-tcp-flags.c \
 	detect-tcp-seq.c \
 	detect-tcp-window.c \
+	detect-tcp-wscale.c \
 	detect-tcphdr.c \
 	detect-tcpmss.c \
 	detect-template.c \

src/detect-engine-register.c

@@ -123,6 +123,7 @@
 #include "detect-flow-pkts.h"
 #include "detect-requires.h"
 #include "detect-tcp-window.h"
+#include "detect-tcp-wscale.h"
 #include "detect-ftpbounce.h"
 #include "detect-ftp-dynamic-port.h"
 #include "detect-isdataat.h"
@@ -707,6 +708,7 @@ void SigTableSetup(void)
     DetectTcphdrRegister();
     DetectUdphdrRegister();
     DetectTcpmssRegister();
+    DetectTcpWscaleRegister();
     DetectICMPv6hdrRegister();
     DetectICMPv6mtuRegister();
     DetectIPAddrBufferRegister();

src/detect-engine-register.h

@@ -289,6 +289,7 @@ enum DetectKeywordId {
     DETECT_TCPHDR,
     DETECT_UDPHDR,
     DETECT_TCPMSS,
+    DETECT_TCP_WSCALE,
     DETECT_FTPDATA,
     DETECT_TARGET,
     DETECT_QUIC_VERSION,

src/detect-tcp-wscale.c

@@ -0,0 +1,172 @@
+/* Copyright (C) 2007-2025 Open Information Security Foundation
+ *
+ * You can copy, redistribute or modify this Program under the terms of
+ * the GNU General Public License version 2 as published by the Free
+ * Software Foundation.
+ *
+ * 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
+ * version 2 along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+/**
+ * \file
+ *
+ * \author Victor Julien <[email protected]>
+ *
+ */
+
+#include "suricata-common.h"
+
+#include "detect.h"
+#include "detect-parse.h"
+#include "detect-engine-prefilter-common.h"
+#include "detect-engine-uint.h"
+#include "util-byte.h"
+
+#include "detect-tcp-wscale.h"
+
+/* prototypes */
+static int DetectTcpWscaleMatch(
+        DetectEngineThreadCtx *, Packet *, const Signature *, const SigMatchCtx *);
+static int DetectTcpWscaleSetup(DetectEngineCtx *, Signature *, const char *);
+void DetectTcpWscaleFree(DetectEngineCtx *, void *);
+static int PrefilterSetupTcpWscale(DetectEngineCtx *de_ctx, SigGroupHead *sgh);
+static bool PrefilterTcpWscaleIsPrefilterable(const Signature *s);
+
+/**
+ * \brief Registration function for tcp.wscale keyword
+ */
+
+void DetectTcpWscaleRegister(void)
+{
+    sigmatch_table[DETECT_TCP_WSCALE].name = "tcp.wscale";
+    sigmatch_table[DETECT_TCP_WSCALE].desc = "match on TCP WSCALE option field";
+    sigmatch_table[DETECT_TCP_WSCALE].url = "/rules/header-keywords.html#tcpwscale";
+    sigmatch_table[DETECT_TCP_WSCALE].Match = DetectTcpWscaleMatch;
+    sigmatch_table[DETECT_TCP_WSCALE].Setup = DetectTcpWscaleSetup;
+    sigmatch_table[DETECT_TCP_WSCALE].Free = DetectTcpWscaleFree;
+    sigmatch_table[DETECT_TCP_WSCALE].SupportsPrefilter = PrefilterTcpWscaleIsPrefilterable;
+    sigmatch_table[DETECT_TCP_WSCALE].SetupPrefilter = PrefilterSetupTcpWscale;
+    sigmatch_table[DETECT_TCP_WSCALE].flags = SIGMATCH_SUPPORT_FIREWALL;
+}
+
+/**
+ * \brief This function is used to match WSCALE rule option on a packet with those passed via
+ * tcp.wscale:
+ *
+ * \param det_ctx pointer to the pattern matcher thread
+ * \param p pointer to the current packet
+ * \param ctx pointer to the sigmatch that we will cast into DetectU8Data
+ *
+ * \retval 0 no match
+ * \retval 1 match
+ */
+static int DetectTcpWscaleMatch(
+        DetectEngineThreadCtx *det_ctx, Packet *p, const Signature *s, const SigMatchCtx *ctx)
+{
+    DEBUG_VALIDATE_BUG_ON(PKT_IS_PSEUDOPKT(p));
+
+    if (!(PacketIsTCP(p)))
+        return 0;
+
+    if (!(TCP_HAS_WSCALE(p)))
+        return 0;
+
+    uint8_t v = TCP_GET_WSCALE(p);
+
+    const DetectU8Data *ws = (const DetectU8Data *)ctx;
+    return DetectU8Match(v, ws);
+}
+
+/**
+ * \brief this function is used to attach the parsed tcp.wscale data into the current signature
+ *
+ * \param de_ctx pointer to the Detection Engine Context
+ * \param s pointer to the Current Signature
+ * \param str pointer to the user provided options
+ *
+ * \retval 0 on Success
+ * \retval -1 on Failure
+ */
+static int DetectTcpWscaleSetup(DetectEngineCtx *de_ctx, Signature *s, const char *str)
+{
+    DetectU8Data *ws = DetectU8Parse(str);
+    if (ws == NULL)
+        return -1;
+
+    if (SCSigMatchAppendSMToList(
+                de_ctx, s, DETECT_TCP_WSCALE, (SigMatchCtx *)ws, DETECT_SM_LIST_MATCH) == NULL) {
+        DetectTcpWscaleFree(de_ctx, ws);
+        return -1;
+    }
+    s->flags |= SIG_FLAG_REQUIRE_PACKET;
+
+    return 0;
+}
+
+/**
+ * \brief this function will free memory associated with DetectU8Data
+ *
+ * \param ptr pointer to DetectU8Data
+ */
+void DetectTcpWscaleFree(DetectEngineCtx *de_ctx, void *ptr)
+{
+    SCDetectU8Free(ptr);
+}
+
+/* prefilter code */
+
+static void PrefilterPacketTcpWscaleMatch(
+        DetectEngineThreadCtx *det_ctx, Packet *p, const void *pectx)
+{
+    DEBUG_VALIDATE_BUG_ON(PKT_IS_PSEUDOPKT(p));
+    if (!(PacketIsTCP(p)))
+        return;
+
+    if (!(TCP_HAS_WSCALE(p)))
+        return;
+
+    const uint8_t v = TCP_GET_WSCALE(p);
+
+    /* during setup Suricata will automatically see if there is another
+     * check that can be added: alproto, sport or dport */
+    const PrefilterPacketHeaderCtx *ctx = pectx;
+    if (!PrefilterPacketHeaderExtraMatch(ctx, p))
+        return;
+
+    DetectU8Data du8;
+    du8.mode = ctx->v1.u8[0];
+    du8.arg1 = ctx->v1.u8[1];
+    du8.arg2 = ctx->v1.u8[2];
+    /* if we match, add all the sigs that use this prefilter. This means
+     * that these will be inspected further */
+    if (DetectU8Match(v, &du8)) {
+        SCLogDebug("packet matches wscale %u", v);
+        PrefilterAddSids(&det_ctx->pmq, ctx->sigs_array, ctx->sigs_cnt);
+    }
+}
+
+static int PrefilterSetupTcpWscale(DetectEngineCtx *de_ctx, SigGroupHead *sgh)
+{
+    return PrefilterSetupPacketHeader(de_ctx, sgh, DETECT_TCP_WSCALE, SIG_MASK_REQUIRE_REAL_PKT,
+            PrefilterPacketU8Set, PrefilterPacketU8Compare, PrefilterPacketTcpWscaleMatch);
+}
+
+static bool PrefilterTcpWscaleIsPrefilterable(const Signature *s)
+{
+    const SigMatch *sm;
+    for (sm = s->init_data->smlists[DETECT_SM_LIST_MATCH]; sm != NULL; sm = sm->next) {
+        switch (sm->type) {
+            case DETECT_TCP_WSCALE:
+                return true;
+        }
+    }
+    return false;
+}

src/detect-tcp-wscale.h

@@ -0,0 +1,29 @@
+/* Copyright (C) 2007-2019 Open Information Security Foundation
+ *
+ * You can copy, redistribute or modify this Program under the terms of
+ * the GNU General Public License version 2 as published by the Free
+ * Software Foundation.
+ *
+ * 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
+ * version 2 along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+/**
+ * \file
+ *
+ * \author Victor Julien <[email protected]>
+ */
+
+#ifndef SURICARA_DETECT_TCP_WSCALE_H
+#define SURICARA_DETECT_TCP_WSCALE_H
+
+void DetectTcpWscaleRegister(void);
+
+#endif /* SURICARA_DETECT_TCP_WSCALE_H */