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Fix hangs reading xml #27

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Fix hangs reading xml #27

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f575507
Fix hangs when reading bad xml
xyzzy42 Jun 10, 2021
c967cd1
Fix hang on unknown element in listen section
xyzzy42 Jun 10, 2021
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12 changes: 8 additions & 4 deletions configuration.c
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Original file line number Diff line number Diff line change
Expand Up @@ -86,11 +86,12 @@ static int configListen(WebdavdConfiguration * config, xmlTextReaderPtr reader,
if (xmlTextReaderNodeType(reader) == XML_READER_TYPE_ELEMENT
&& !strcmp(xmlTextReaderConstNamespaceUri(reader),
CONFIG_NAMESPACE)) {
if (!strcmp(xmlTextReaderConstLocalName(reader), "port")) {
const char * elementName = xmlTextReaderConstLocalName(reader);
if (!strcmp(elementName, "port")) {
result = readConfigInt(reader, &config->daemons[index].port, configFile);
} else if (!strcmp(xmlTextReaderConstLocalName(reader), "host")) {
} else if (!strcmp(elementName, "host")) {
result = readConfigString(reader, &config->daemons[index].host);
} else if (!strcmp(xmlTextReaderConstLocalName(reader), "encryption")) {
} else if (!strcmp(elementName, "encryption")) {
const char * encryptionString;
result = stepOverText(reader, &encryptionString);
if (encryptionString) {
Expand All @@ -104,7 +105,7 @@ static int configListen(WebdavdConfiguration * config, xmlTextReaderPtr reader,
}
xmlFree((char *) encryptionString);
}
} else if (!strcmp(xmlTextReaderConstLocalName(reader), "forward-to")) {
} else if (!strcmp(elementName, "forward-to")) {
int depth2 = xmlTextReaderDepth(reader) + 1;
result = stepInto(reader);
config->daemons[index].forwardToIsEncrypted = -1;
Expand Down Expand Up @@ -143,6 +144,9 @@ static int configListen(WebdavdConfiguration * config, xmlTextReaderPtr reader,
config->daemons[index].forwardToPort == 443 ? 1 : 0;
}
}
} else {
stdLogError(0, "Unknown element tag '%s' in listen section", elementName);
result = stepOver(reader);
}
} else {
result = stepOver(reader);
Expand Down
20 changes: 10 additions & 10 deletions xml.c
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Original file line number Diff line number Diff line change
Expand Up @@ -23,54 +23,54 @@ int stepInto(xmlTextReaderPtr reader) {
int result;
do {
result = xmlTextReaderRead(reader);
} while (result
} while (result > 0
&& (xmlTextReaderNodeType(reader) == XML_READER_TYPE_SIGNIFICANT_WHITESPACE
|| xmlTextReaderNodeType(reader) == XML_READER_TYPE_COMMENT
|| xmlTextReaderNodeType(reader) == XML_READER_TYPE_END_ELEMENT));
return result;
return result > 0;
}

int stepOver(xmlTextReaderPtr reader) {
int depth = xmlTextReaderDepth(reader);
int result;
do {
result = xmlTextReaderRead(reader);
} while (result && xmlTextReaderDepth(reader) > depth);
while (result
} while (result > 0 && xmlTextReaderDepth(reader) > depth);
while (result > 0
&& (xmlTextReaderNodeType(reader) == XML_READER_TYPE_SIGNIFICANT_WHITESPACE
|| xmlTextReaderNodeType(reader) == XML_READER_TYPE_COMMENT
|| xmlTextReaderNodeType(reader) == XML_READER_TYPE_END_ELEMENT)) {
result = xmlTextReaderRead(reader);
}
return result;
return result > 0;
}

int stepOut(xmlTextReaderPtr reader) {
int depth = xmlTextReaderDepth(reader) - 1;
int result;
do {
result = xmlTextReaderRead(reader);
} while (result && xmlTextReaderDepth(reader) > depth);
while (result
} while (result > 0 && xmlTextReaderDepth(reader) > depth);
while (result > 0
&& (xmlTextReaderNodeType(reader) == XML_READER_TYPE_SIGNIFICANT_WHITESPACE
|| xmlTextReaderNodeType(reader) == XML_READER_TYPE_COMMENT
|| xmlTextReaderNodeType(reader) == XML_READER_TYPE_END_ELEMENT)) {
result = xmlTextReaderRead(reader);
}
return result;
return result > 0;
}

int stepOverText(xmlTextReaderPtr reader, const char ** text) {
int depth = xmlTextReaderDepth(reader);
int result = stepInto(reader);
*text = NULL;
if (result && xmlTextReaderDepth(reader) > depth) {
if (result > 0 && xmlTextReaderDepth(reader) > depth) {
if (xmlTextReaderNodeType(reader) == XML_READER_TYPE_TEXT) {
*text = xmlTextReaderValue(reader);
}
result = stepOut(reader);
}
return result;
return result > 0;
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@couling couling Jun 10, 2021 •
edited
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I don't know why I missed error handling in this code, that's a bit of a mystery.

However the fix shouldn't deviate from the return codes in libxml2:

Returns: 1 if the node was read successfully, 0 if there is no more nodes to read, or -1 in case of error

In other words 0 means EOF and -1 mean error. For the line return result > 0 fixes the immediate problem of other calls failing to check error, the fix should really be to simply return result and fix those other lines. That lets the code exit(1) at an appropriate point.

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The existing code handles it ok, it'll skip the problem section and continue parsing. If this returns -1, then all the code using this needs to be updated too, so it detects errors and handles them specially.

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Yeah. Sadly that's what it needs. :-(
I'll try to assess how much damage this will do to the rest of the code. It might not be so bad.

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I've tested a bunch of different errors and it's decent what happens. It doesn't abort, but the parts that aren't bad work ok and it starts. IMHO, it would be better to abort on any error and produce a clear message about it.

}

int elementMatches(xmlTextReaderPtr reader, const char * namespace, const char * nodeName) {
Expand Down