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Check for invalid redeclarations of predefined entities

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Implement section "4.6 Predefined Entities" of the XML 1.0 spec and
check whether redeclarations of predefined entities match the original
definitions.

Note that some test cases declared

    <!ENTITY lt "<">

But the XML spec clearly states that this is illegal:

> If the entities lt or amp are declared, they MUST be declared as
> internal entities whose replacement text is a character reference to
> the respective character (less-than sign or ampersand) being escaped;
> the double escaping is REQUIRED for these entities so that references
> to them produce a well-formed result.

Also fixes #217 but the connection is only tangential. The integer
overflow discovered by fuzzing was more related to the fact that various
parts of the parser disagreed on whether to prefer predefined entities
over their redeclarations. The whole situation is a mess and even
depends on legacy parser options. But now that redeclarations are
validated, it shouldn't make a difference.

As noted in the added comment, this is also one of the cases where
overly defensive checks can hide interesting logic bugs from fuzzers.
This commit is contained in:
Nick Wellnhofer 2021-02-08 20:58:32 +01:00
parent 07920b4381
commit 01411e7c5e
15 changed files with 137 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

39
entities.c
View File

@ -210,7 +210,7 @@ xmlAddEntity(xmlDtdPtr dtd, const xmlChar *name, int type,
const xmlChar *content) {
xmlDictPtr dict = NULL;
xmlEntitiesTablePtr table = NULL;
xmlEntityPtr ret;
xmlEntityPtr ret, predef;
if (name == NULL)
return(NULL);
@ -223,6 +223,43 @@ xmlAddEntity(xmlDtdPtr dtd, const xmlChar *name, int type,
case XML_INTERNAL_GENERAL_ENTITY:
case XML_EXTERNAL_GENERAL_PARSED_ENTITY:
case XML_EXTERNAL_GENERAL_UNPARSED_ENTITY:
predef = xmlGetPredefinedEntity(name);
if (predef != NULL) {
int valid = 0;
/* 4.6 Predefined Entities */
if (type == XML_INTERNAL_GENERAL_ENTITY) {
int c = predef->content[0];
if (((content[0] == c) && (content[1] == 0)) &&
((c == '>') || (c == '\'') || (c == '"'))) {
valid = 1;
} else if ((content[0] == '&') && (content[1] == '#')) {
if (content[2] == 'x') {
xmlChar *hex = BAD_CAST "0123456789ABCDEF";
xmlChar ref[] = "00;";
ref[0] = hex[c / 16 % 16];
ref[1] = hex[c % 16];
if (xmlStrcasecmp(&content[3], ref) == 0)
valid = 1;
} else {
xmlChar ref[] = "00;";
ref[0] = '0' + c / 10 % 10;
ref[1] = '0' + c % 10;
if (xmlStrEqual(&content[2], ref))
valid = 1;
}
}
}
if (!valid) {
xmlEntitiesErr(XML_ERR_ENTITY_PROCESSING,
"xmlAddEntity: invalid redeclaration of predefined"
" entity");
return(NULL);
}
}
if (dtd->entities == NULL)
dtd->entities = xmlHashCreateDict(0, dict);
table = dtd->entities;

9
result/ent6hex Normal file
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@ -0,0 +1,9 @@
<?xml version="1.0"?>
<!DOCTYPE doc [
<!ENTITY lt "&#x26;#x3c;">
<!ENTITY gt "&#x26;#x3E;">
<!ENTITY amp "&#x26;#x26;">
<!ENTITY apos "&#x26;#x27;">
<!ENTITY quot "&#x26;#x22;">
]>
<doc/>

2
result/ent6hex.rde Normal file
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@ -0,0 +1,2 @@
0 10 doc 0 0
0 1 doc 1 0

2
result/ent6hex.rdr Normal file
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@ -0,0 +1,2 @@
0 10 doc 0 0
0 1 doc 1 0

17
result/ent6hex.sax Normal file
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@ -0,0 +1,17 @@
SAX.setDocumentLocator()
SAX.startDocument()
SAX.internalSubset(doc, , )
SAX.entityDecl(lt, 1, (null), (null), &#x3c;)
SAX.getEntity(lt)
SAX.entityDecl(gt, 1, (null), (null), &#x3E;)
SAX.getEntity(gt)
SAX.entityDecl(amp, 1, (null), (null), &#x26;)
SAX.getEntity(amp)
SAX.entityDecl(apos, 1, (null), (null), &#x27;)
SAX.getEntity(apos)
SAX.entityDecl(quot, 1, (null), (null), &#x22;)
SAX.getEntity(quot)
SAX.externalSubset(doc, , )
SAX.startElement(doc)
SAX.endElement(doc)
SAX.endDocument()

17
result/ent6hex.sax2 Normal file
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@ -0,0 +1,17 @@
SAX.setDocumentLocator()
SAX.startDocument()
SAX.internalSubset(doc, , )
SAX.entityDecl(lt, 1, (null), (null), &#x3c;)
SAX.getEntity(lt)
SAX.entityDecl(gt, 1, (null), (null), &#x3E;)
SAX.getEntity(gt)
SAX.entityDecl(amp, 1, (null), (null), &#x26;)
SAX.getEntity(amp)
SAX.entityDecl(apos, 1, (null), (null), &#x27;)
SAX.getEntity(apos)
SAX.entityDecl(quot, 1, (null), (null), &#x22;)
SAX.getEntity(quot)
SAX.externalSubset(doc, , )
SAX.startElementNs(doc, NULL, NULL, 0, 0, 0)
SAX.endElementNs(doc, NULL, NULL)
SAX.endDocument()

2
result/errors/759398.xml.str
View File

@ -1,5 +1,5 @@
./test/errors/759398.xml:210: parser error : internal error: detected an error in element content
need to worry about parsers whi<! don't expand
need to worry about parsers whi<! don't expand PErefs finding
^
./test/errors/759398.xml : failed to parse

9
result/noent/ent6hex Normal file
View File

@ -0,0 +1,9 @@
<?xml version="1.0"?>
<!DOCTYPE doc [
<!ENTITY lt "&#x26;#x3c;">
<!ENTITY gt "&#x26;#x3E;">
<!ENTITY amp "&#x26;#x26;">
<!ENTITY apos "&#x26;#x27;">
<!ENTITY quot "&#x26;#x22;">
]>
<doc/>

17
result/noent/ent6hex.sax2 Normal file
View File

@ -0,0 +1,17 @@
SAX.setDocumentLocator()
SAX.startDocument()
SAX.internalSubset(doc, , )
SAX.entityDecl(lt, 1, (null), (null), &#x3c;)
SAX.getEntity(lt)
SAX.entityDecl(gt, 1, (null), (null), &#x3E;)
SAX.getEntity(gt)
SAX.entityDecl(amp, 1, (null), (null), &#x26;)
SAX.getEntity(amp)
SAX.entityDecl(apos, 1, (null), (null), &#x27;)
SAX.getEntity(apos)
SAX.entityDecl(quot, 1, (null), (null), &#x22;)
SAX.getEntity(quot)
SAX.externalSubset(doc, , )
SAX.startElementNs(doc, NULL, NULL, 0, 0, 0)
SAX.endElementNs(doc, NULL, NULL)
SAX.endDocument()

2
result/valid/REC-xml-19980210.xml
View File

@ -10,7 +10,7 @@ publication. --><!ENTITY XML.version "1.0">
<!ENTITY draft.month "February">
<!ENTITY draft.year "1998">
<!ENTITY WebSGML "WebSGML Adaptations Annex to ISO 8879">
<!ENTITY lt "<">
<!ENTITY lt "&#38;#60;">
<!ENTITY gt ">">
<!ENTITY xmlpio "'&lt;?xml'">
<!ENTITY pic "'?>'">

8
test/ent6hex Normal file
View File

@ -0,0 +1,8 @@
<!DOCTYPE doc [
<!ENTITY lt "&#x26;#x3c;">
<!ENTITY gt "&#x26;#x3E;">
<!ENTITY amp "&#x26;#x26;">
<!ENTITY apos "&#x26;#x27;">
<!ENTITY quot "&#x26;#x22;">
]>
<doc/>

2
test/errors/759398.xml
View File

@ -18,7 +18,7 @@ publication. -->
<!ENTITY WebSGML
'WebSGML Adaptations Annex to ISO 8879'>
<!ENTITY lt "<">
<!ENTITY lt "&#38;#60;">
<!ENTITY gt ">">
<!ENTITY xmlpio "'&lt;?xml'">
<!ENTITY pic "'?>'">

2
test/relaxng/tutor11_1_3.xml
View File

@ -18,7 +18,7 @@ publication. -->
<!ENTITY WebSGML
'WebSGML Adaptations Annex to ISO 8879'>
<!ENTITY lt "<">
<!ENTITY lt "&#38;#60;">
<!ENTITY gt ">">
<!ENTITY xmlpio "'&lt;?xml'">
<!ENTITY pic "'?>'">

2
test/valid/REC-xml-19980210.xml
View File

@ -18,7 +18,7 @@ publication. -->
<!ENTITY WebSGML
'WebSGML Adaptations Annex to ISO 8879'>
<!ENTITY lt "<">
<!ENTITY lt "&#38;#60;">
<!ENTITY gt ">">
<!ENTITY xmlpio "'&lt;?xml'">
<!ENTITY pic "'?>'">

13
tree.c
View File

@ -1310,6 +1310,16 @@ xmlStringLenGetNodeList(const xmlDoc *doc, const xmlChar *value, int len) {
else
tmp = 0;
while (tmp != ';') { /* Non input consuming loop */
/*
* If you find an integer overflow here when fuzzing,
* the bug is probably elsewhere. This function should
* only receive entities that were already validated by
* the parser, typically by xmlParseAttValueComplex
* calling xmlStringDecodeEntities.
*
* So it's better *not* to check for overflow to
* potentially discover new bugs.
*/
if ((tmp >= '0') && (tmp <= '9'))
charval = charval * 16 + (tmp - '0');
else if ((tmp >= 'a') && (tmp <= 'f'))
@ -1338,6 +1348,7 @@ xmlStringLenGetNodeList(const xmlDoc *doc, const xmlChar *value, int len) {
else
tmp = 0;
while (tmp != ';') { /* Non input consuming loops */
/* Don't check for integer overflow, see above. */
if ((tmp >= '0') && (tmp <= '9'))
charval = charval * 10 + (tmp - '0');
else {
@ -1517,6 +1528,7 @@ xmlStringGetNodeList(const xmlDoc *doc, const xmlChar *value) {
cur += 3;
tmp = *cur;
while (tmp != ';') { /* Non input consuming loop */
/* Don't check for integer overflow, see above. */
if ((tmp >= '0') && (tmp <= '9'))
charval = charval * 16 + (tmp - '0');
else if ((tmp >= 'a') && (tmp <= 'f'))
@ -1539,6 +1551,7 @@ xmlStringGetNodeList(const xmlDoc *doc, const xmlChar *value) {
cur += 2;
tmp = *cur;
while (tmp != ';') { /* Non input consuming loops */
/* Don't check for integer overflow, see above. */
if ((tmp >= '0') && (tmp <= '9'))
charval = charval * 10 + (tmp - '0');
else {