xpath.c

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/*
 * Copyright 2004-2020 the Pacemaker project contributors
 *
 * The version control history for this file may have further details.
 *
 * This source code is licensed under the GNU Lesser General Public License
 * version 2.1 or later (LGPLv2.1+) WITHOUT ANY WARRANTY.
 */

#include <crm_internal.h>
#include <stdio.h>
#include <string.h>
#include <crm/msg_xml.h>
#include "crmcommon_private.h"

/*
 * From xpath2.c
 *
 * All the elements returned by an XPath query are pointers to
 * elements from the tree *except* namespace nodes where the XPath
 * semantic is different from the implementation in libxml2 tree.
 * As a result when a returned node set is freed when
 * xmlXPathFreeObject() is called, that routine must check the
 * element type. But node from the returned set may have been removed
 * by xmlNodeSetContent() resulting in access to freed data.
 *
 * This can be exercised by running
 *       valgrind xpath2 test3.xml '//discarded' discarded
 *
 * There is 2 ways around it:
 *   - make a copy of the pointers to the nodes from the result set
 *     then call xmlXPathFreeObject() and then modify the nodes
 * or
 * - remove the references from the node set, if they are not
       namespace nodes, before calling xmlXPathFreeObject().
 */
void
freeXpathObject(xmlXPathObjectPtr xpathObj)
{
    int lpc, max = numXpathResults(xpathObj);

    if (xpathObj == NULL) {
        return;
    }

    for (lpc = 0; lpc < max; lpc++) {
        if (xpathObj->nodesetval->nodeTab[lpc] && xpathObj->nodesetval->nodeTab[lpc]->type != XML_NAMESPACE_DECL) {
            xpathObj->nodesetval->nodeTab[lpc] = NULL;
        }
    }

    /* _Now_ it's safe to free it */
    xmlXPathFreeObject(xpathObj);
}

xmlNode *
getXpathResult(xmlXPathObjectPtr xpathObj, int index)
{
    xmlNode *match = NULL;
    int max = numXpathResults(xpathObj);

    CRM_CHECK(index >= 0, return NULL);
    CRM_CHECK(xpathObj != NULL, return NULL);

    if (index >= max) {
        crm_err("Requested index %d of only %d items", index, max);
        return NULL;

    } else if(xpathObj->nodesetval->nodeTab[index] == NULL) {
        /* Previously requested */
        return NULL;
    }

    match = xpathObj->nodesetval->nodeTab[index];
    CRM_CHECK(match != NULL, return NULL);

    if (xpathObj->nodesetval->nodeTab[index]->type != XML_NAMESPACE_DECL) {
        /* See the comment for freeXpathObject() */
        xpathObj->nodesetval->nodeTab[index] = NULL;
    }

    if (match->type == XML_DOCUMENT_NODE) {
        /* Will happen if section = '/' */
        match = match->children;

    } else if (match->type != XML_ELEMENT_NODE
               && match->parent && match->parent->type == XML_ELEMENT_NODE) {
        /* Return the parent instead */
        match = match->parent;

    } else if (match->type != XML_ELEMENT_NODE) {
        /* We only support searching nodes */
        crm_err("We only support %d not %d", XML_ELEMENT_NODE, match->type);
        match = NULL;
    }
    return match;
}

void
dedupXpathResults(xmlXPathObjectPtr xpathObj)
{
    int lpc, max = numXpathResults(xpathObj);

    if (xpathObj == NULL) {
        return;
    }

    for (lpc = 0; lpc < max; lpc++) {
        xmlNode *xml = NULL;
        gboolean dedup = FALSE;

        if (xpathObj->nodesetval->nodeTab[lpc] == NULL) {
            continue;
        }

        xml = xpathObj->nodesetval->nodeTab[lpc]->parent;

        for (; xml; xml = xml->parent) {
            int lpc2 = 0;

            for (lpc2 = 0; lpc2 < max; lpc2++) {
                if (xpathObj->nodesetval->nodeTab[lpc2] == xml) {
                    xpathObj->nodesetval->nodeTab[lpc] = NULL;
                    dedup = TRUE;
                    break;
                }
            }

            if (dedup) {
                break;
            }
        }
    }
}

/* the caller needs to check if the result contains a xmlDocPtr or xmlNodePtr */
xmlXPathObjectPtr
xpath_search(xmlNode * xml_top, const char *path)
{
    xmlDocPtr doc = NULL;
    xmlXPathObjectPtr xpathObj = NULL;
    xmlXPathContextPtr xpathCtx = NULL;
    const xmlChar *xpathExpr = (pcmkXmlStr) path;

    CRM_CHECK(path != NULL, return NULL);
    CRM_CHECK(xml_top != NULL, return NULL);
    CRM_CHECK(strlen(path) > 0, return NULL);

    doc = getDocPtr(xml_top);

    xpathCtx = xmlXPathNewContext(doc);
    CRM_ASSERT(xpathCtx != NULL);

    xpathObj = xmlXPathEvalExpression(xpathExpr, xpathCtx);
    xmlXPathFreeContext(xpathCtx);
    return xpathObj;
}

void
crm_foreach_xpath_result(xmlNode *xml, const char *xpath,
                         void (*helper)(xmlNode*, void*), void *user_data)
{
    xmlXPathObjectPtr xpathObj = xpath_search(xml, xpath);
    int nresults = numXpathResults(xpathObj);
    int i;

    for (i = 0; i < nresults; i++) {
        xmlNode *result = getXpathResult(xpathObj, i);

        CRM_LOG_ASSERT(result != NULL);
        if (result) {
            (*helper)(result, user_data);
        }
    }
    freeXpathObject(xpathObj);
}

xmlNode *
get_xpath_object_relative(const char *xpath, xmlNode * xml_obj, int error_level)
{
    xmlNode *result = NULL;
    char *xpath_full = NULL;
    char *xpath_prefix = NULL;

    if (xml_obj == NULL || xpath == NULL) {
        return NULL;
    }

    xpath_prefix = (char *)xmlGetNodePath(xml_obj);

    xpath_full = crm_strdup_printf("%s%s", xpath_prefix, xpath);

    result = get_xpath_object(xpath_full, xml_obj, error_level);

    free(xpath_prefix);
    free(xpath_full);
    return result;
}

xmlNode *
get_xpath_object(const char *xpath, xmlNode * xml_obj, int error_level)
{
    int max;
    xmlNode *result = NULL;
    xmlXPathObjectPtr xpathObj = NULL;
    char *nodePath = NULL;
    char *matchNodePath = NULL;

    if (xpath == NULL) {
        return xml_obj;         /* or return NULL? */
    }

    xpathObj = xpath_search(xml_obj, xpath);
    nodePath = (char *)xmlGetNodePath(xml_obj);
    max = numXpathResults(xpathObj);

    if (max < 1) {
        if (error_level < LOG_NEVER) {
            do_crm_log(error_level, "No match for %s in %s",
                       xpath, crm_str(nodePath));
            crm_log_xml_explicit(xml_obj, "Unexpected Input");
        }

    } else if (max > 1) {
        if (error_level < LOG_NEVER) {
            int lpc = 0;

            do_crm_log(error_level, "Too many matches for %s in %s",
                       xpath, crm_str(nodePath));

            for (lpc = 0; lpc < max; lpc++) {
                xmlNode *match = getXpathResult(xpathObj, lpc);

                CRM_LOG_ASSERT(match != NULL);
                if (match != NULL) {
                    matchNodePath = (char *) xmlGetNodePath(match);
                    do_crm_log(error_level, "%s[%d] = %s",
                               xpath, lpc, crm_str(matchNodePath));
                    free(matchNodePath);
                }
            }
            crm_log_xml_explicit(xml_obj, "Bad Input");
        }

    } else {
        result = getXpathResult(xpathObj, 0);
    }

    freeXpathObject(xpathObj);
    free(nodePath);

    return result;
}

int
pcmk__element_xpath(const char *prefix, xmlNode *xml, char *buffer,
                    int offset, size_t buffer_size)
{
    const char *id = ID(xml);

    if(offset == 0 && prefix == NULL && xml->parent) {
        offset = pcmk__element_xpath(NULL, xml->parent, buffer, offset,
                                     buffer_size);
    }

    if(id) {
        offset += snprintf(buffer + offset, buffer_size - offset,
                           "/%s[@id='%s']", (const char *) xml->name, id);
    } else if(xml->name) {
        offset += snprintf(buffer + offset, buffer_size - offset,
                           "/%s", (const char *) xml->name);
    }

    return offset;
}

char *
xml_get_path(xmlNode *xml)
{
    int offset = 0;
    char buffer[PCMK__BUFFER_SIZE];

    if (pcmk__element_xpath(NULL, xml, buffer, offset, sizeof(buffer)) > 0) {
        return strdup(buffer);
    }
    return NULL;
}