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The previous work for unbounded memory usage and overflows on the buffer
API had several shortcomings:
1. The total size of the buffer was limited by arbitrarily small
precision on the storage type for buffer indexes (typedef'd as
`bufsize_t`). This is not a good design pattern in secure applications,
particualarly since it requires the addition of helper functions to cast
to/from the native `size` types and the custom type for the buffer, and
check for overflows.
2. The library was calling `abort` on overflow and memory allocation
failures. This is not a good practice for production libraries, since it
turns a potential RCE into a trivial, guaranteed DoS to the whole
application that is linked against the library. It defeats the whole
point of performing overflow or allocation checks when the checks will
crash the library and the enclosing program anyway.
3. The default size limits for buffers were essentially unbounded
(capped to the precision of the storage type) and could lead to DoS
attacks by simple memory exhaustion (particularly critical in 32-bit
platforms). This is not a good practice for a library that handles
arbitrary user input.
Hence, this patchset provides slight (but in my opinion critical)
improvements on this area, copying some of the patterns we've used in
the past for high throughput, security sensitive Markdown parsers:
1. The storage type for buffer sizes is now platform native (`ssize_t`).
Ideally, this would be a `size_t`, but several parts of the code expect
buffer indexes to be possibly negative. Either way, switching to a
`size` type is an strict improvement, particularly in 64-bit platforms.
All the helpers that assured that values cannot escape the `size` range
have been removed, since they are superfluous.
2. The overflow checks have been removed. Instead, the maximum size for
a buffer has been set to a safe value for production usage (32mb) that
can be proven not to overflow in practice. Users that need to parse
particularly large Markdown documents can increase this value. A static,
compile-time check has been added to ensure that the maximum buffer size
cannot overflow on any growth operations.
3. The library no longer aborts on buffer overflow. The CMark library
now follows the convention of other Markdown implementations (such as
Hoedown and Sundown) and silently handles buffer overflows and
allocation failures by dropping data from the buffer. The result is
that pathological Markdown documents that try to exploit the library
will instead generate truncated (but valid, and safe) outputs.
All tests after these small refactorings have been verified to pass.
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NOTE: Regarding 32 bit overflows, generating test cases that crash the
library is trivial (any input document larger than 2gb will crash
CMark), but most Python implementations have issues with large strings
to begin with, so a test case cannot be added to the pathological tests
suite, since it's written in Python.
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ALso don't set CMARK_INLINE to __inline if we're compiling
under MSVC in cplusplus mode.
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have the same set of disabled warnings
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* Reformatted all source files.
* Added 'format' target to Makefile.
* Removed 'astyle' target.
* Updated .editorconfig.
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There are probably a couple of places I missed. But this will only
be a problem if we use a 64-bit bufsize_t at some point. Then, we'll
get warnings from -Wshorten-64-to-32.
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Supersedes pull request #34.
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Otherwise cmark's behavior varies unpredictably with the locale.
`is_punctuation` in utf8.h has also been adjusted so that everything
that counts all ASCII symbol characters count as punctuation, even
though some are not in P* character classes.
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Reverts 225d720.
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This isn't needed any more since we don't expose these in the API.
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Since chunk.h and buffer.h are private now, there's no need to optionally
disable the short name macros.
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The approach I'm taking is to copy inline literals internally to
NULL-terminated C strings if requested by an accessor. This allows to
return a 'const char *' that doesn't have to be freed by the caller.
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Needed for C++ compatibility.
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- Test for NULL after allocation
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