detect/pcrexform: New transform: applies RE

This commit adds a new transform -- pcrexform -- that applies a regular
expression to the transformation buffer. If an expression was captured,
that is output to the transformation buffer. Otherwise, the
transformation buffer is unchanged.

src/detect-transform-pcrexform.c

@@ -0,0 +1,110 @@
+/* Copyright (C) 2020 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 Jeff Lucovsky <jeff@lucovsky.org>
+ *
+ * Implements the pcrexform transform keyword with option support
+ */
+
+#include "suricata-common.h"
+
+#include "detect.h"
+#include "detect-engine.h"
+#include "detect-parse.h"
+#include "detect-transform-pcrexform.h"
+
+typedef DetectParseRegex DetectTransformPcrexformData;
+
+static int DetectTransformPcrexformSetup (DetectEngineCtx *, Signature *, const char *);
+static void DetectTransformPcrexformFree(DetectEngineCtx *, void *);
+static void DetectTransformPcrexform(InspectionBuffer *buffer, void *options);
+
+void DetectTransformPcrexformRegister(void)
+{
+    sigmatch_table[DETECT_TRANSFORM_PCREXFORM].name = "pcrexform";
+    sigmatch_table[DETECT_TRANSFORM_PCREXFORM].desc =
+        "modify buffer via PCRE before inspection";
+    sigmatch_table[DETECT_TRANSFORM_PCREXFORM].url = "/rules/transforms.html#pcre-xform";
+    sigmatch_table[DETECT_TRANSFORM_PCREXFORM].Transform =
+        DetectTransformPcrexform;
+    sigmatch_table[DETECT_TRANSFORM_PCREXFORM].Free =
+        DetectTransformPcrexformFree;
+    sigmatch_table[DETECT_TRANSFORM_PCREXFORM].Setup =
+        DetectTransformPcrexformSetup;
+    sigmatch_table[DETECT_TRANSFORM_PCREXFORM].flags |= SIGMATCH_QUOTES_MANDATORY;
+}
+
+static void DetectTransformPcrexformFree(DetectEngineCtx *de_ctx, void *ptr)
+{
+    if (ptr != NULL) {
+        DetectTransformPcrexformData *pxd = (DetectTransformPcrexformData *) ptr;
+        SCFree(pxd);
+    }
+}
+/**
+ *  \internal
+ *  \brief Apply the pcrexform keyword to the last pattern match
+ *  \param det_ctx detection engine ctx
+ *  \param s signature
+ *  \param regexstr options string
+ *  \retval 0 ok
+ *  \retval -1 failure
+ */
+static int DetectTransformPcrexformSetup (DetectEngineCtx *de_ctx, Signature *s, const char *regexstr)
+{
+    SCEnter();
+
+    // Create pxd from regexstr
+    DetectTransformPcrexformData *pxd = SCCalloc(sizeof(*pxd), 1);
+    if (pxd == NULL) {
+        SCLogDebug("pxd allocation failed");
+        SCReturnInt(-1);
+    }
+
+    DetectSetupParseRegexes(regexstr, pxd);
+
+    int r = DetectSignatureAddTransform(s, DETECT_TRANSFORM_PCREXFORM, pxd);
+    if (r != 0) {
+        SCFree(pxd);
+    }
+
+    SCReturnInt(r);
+}
+
+static void DetectTransformPcrexform(InspectionBuffer *buffer, void *options)
+{
+    const char *input = (const char *)buffer->inspect;
+    const uint32_t input_len = buffer->inspect_len;
+    DetectTransformPcrexformData *pxd = options;
+
+    int ov[MAX_SUBSTRINGS];
+    int ret = DetectParsePcreExecLen(pxd, input, input_len, 0, 0, ov, MAX_SUBSTRINGS);
+
+    if (ret > 0) {
+        const char *str;
+        ret = pcre_get_substring((char *) buffer->inspect, ov,
+                                  MAX_SUBSTRINGS, ret - 1, &str);
+
+        if (ret >= 0) {
+            InspectionBufferCopy(buffer, (uint8_t *)str, (uint32_t) ret);
+            pcre_free_substring(str);
+        }
+    }
+}

src/detect-transform-pcrexform.h

@@ -0,0 +1,30 @@
+/* Copyright (C) 2020 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 Jeff Lucovsky <jeff@lucovsky.org
+ */
+
+#ifndef __DETECT_TRANSFORM_PCREXFORM_H__
+#define __DETECT_TRANSFORM_PCREXFORM_H__
+
+/* prototypes */
+void DetectTransformPcrexformRegister (void);
+
+#endif /* __DETECT_TRANSFORM_PCREXFORM_H__ */