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In xpath.c there's a lot of code like:
valuePush(ctxt, xmlCacheNewX());
...
valuePop(ctxt);
If xmlCacheNewX fails, no value will be pushed on the stack. If there's
no error check in between, valuePop will pop an unrelated value which
can lead to use-after-free errors.
Instead of trying to fix all call sites, we simply stop popping values
if an error was signaled. This requires to change the CHECK_TYPE macro
which is often used to determine whether a value can be safely popped.
Found with libFuzzer, see #344.
Reporting errors is expensive and some abusive test cases can generate
an error for each invalid input byte. This causes the parser to spend
most of the time with error handling. Limit the number of errors and
warnings to 100.
This commit implements robust detection of entity amplification attacks,
better known as the "billion laughs" attack.
We now limit the size of the document after substitution of entities to
10 times the size before expansion. This guarantees linear behavior by
definition. There already was a similar check before, but the accounting
of "sizeentities" (size of external entities) and "sizeentcopy" (size of
all copies created by entity references) wasn't accurate.
We also need saturation arithmetic since we're historically limited to
"unsigned long" which is 32-bit on many platforms.
A maximum of 10 MB of substitutions is always allowed. This should make
use cases like DITA work which have caused problems in the past.
The old checks based on the number of entities were removed. This is
accounted for by adding a fixed cost to each entity reference.
Entity amplification checks are now enabled even if XML_PARSE_HUGE is
set. This option is mainly used to allow larger text nodes. Most users
were unaware that it also disabled entity expansion checks.
Some of the limits might be adjusted later. If this change turns out to
affect legitimate use cases, we can add a separate parser option to
disable the checks.
Fixes#294.
Fixes#345.
Instead of abusing the LSB of the "checked" member, store the result
of testing for occurrence of '<' character in "flags".
Also use the flags in xmlParseStringEntityRef instead of rescanning
every time.
To check whether an entity was already parsed, the code previously
tested whether "checked" was non-zero or "children" was non-null. The
"children" check could be unreliable because an empty entity also
results in an empty (NULL) node list. Use a separate flag to make this
check more reliable.
This was an experimental and undocumented micro-optimization for
Windows which apparently required different calling conventions for
variable-argument functions, making it impossible to maintain without
domain knowledge.
Define XML_IGNORE_DEPRECATION_WARNINGS and the corresponding XML_POP_WARNINGS
for Visual Studio, and consequently define XML_IGNORE_FPTR_CAST_WARNINGS so
that we do not get a compiler warning on Visual Studio by doing a
__pragma(warning(pop)) without a corresponding __pragma(warning(push)).
Also correct the documentation a bit for XML_POP_WARNINGS.
We can mark APIs as deprecated using __declspec(deprecated) with Visual Studio
2005 and later, so add a definition of that so that we can help users avoid
using deprecated APIs when using Visual Studio as well.
For the existing GCC definition, check whether we are on GCC 3.1+ before
enabling the definition.
Remove inaccurate xmlParseCheckTransition check.
Remove non-incremental xmlParseGetLasts check.
Add functions that check for several boundary constructs more
accurately, keeping track of progress in ctxt->checkIndex.
Fixes#439.
In some cases, for example when using encoders, the read callback was
set to NULL, in other cases it was set to xmlInputReadCallbackNop.
xmlGROW only tested for xmlInputReadCallbackNop, resulting in errors
when parsing large encoded content from memory.
Always use a NULL callback for memory buffers to avoid ambiguities.
Fixes#262.
When using xmlreader, XPointer expressions in XIncludes simply cannot
work. Expressions can reference nodes which weren't parsed yet or which
were already deleted.
After fixing nested XIncludes, we reference includes which were parsed
previously. When streaming, these nodes could have been deleted, leading
to use-after-free errors.
Disallow XPointer expressions and truncate the include table in
streaming mode.
Private functions were previously declared
- in header files in the root directory
- in public headers guarded with IN_LIBXML
- in libxml.h
- redundantly in source files that used them.
Consolidate all private header files in include/private.
