The hIST chunks, used for storing image histograms, contain arrays of
16-bit unsigned integers, and the chunk size is expected to be an even
number. Raise a png_chunk_benign_error() if a hIST chunk fails to meet
this expectation.
Reported-by: Eugene Kliuchnikov <eustas@google.com>
The following pointer subtraction was unnecessary:
((const char*)(ptr)-(const char*)0)
In order to avoid further warnings about casting a wide pointer type
to a narrower integer type, we cast the pointer to the target integer
type through (size_t).
Also fix a comment and reformat the surrounding code.
Problem description:
Imagine a bitstream with an eXIf data segment that has invalid CRC.
If png_crc_finish() fails at line 2090, info_ptr->eXIf_buf is not freed
(despite the free_me setting at line 2062) because png_free_data() is
not called. png_read_info() is actually looping several time over the
png_eXIf chunk, calling png_handle_eXIf() several time in a row without
freeing the buffer.
This patch fixes the problem by leaving info_ptr's content in a clean
state in case of failure, as it is done at line 2084.
As per the const correctness rules, top-level const-ness of data
in automatic scopes does not propagate outside of these scopes
(unlike const-ness at lower levels, such as pointers to const data).
Previously, const was used liberally, but inconsistently across the
libpng codebase. Using const wherever applicable is not incorrect.
However, _consistent_ use of const is difficult to maintain in such
conditions.
In conclusion, we shall continue to use const only where doing so is
strictly necessary:
1. If a function guarantees that it will not modify an argument
passed by pointer, the corresponding function parameter should be
a pointer-to-const (const T *).
2. Static data should not be modified, therefore it should be const.
Reference:
Google C++ Style Guide
https://google.github.io/styleguide/cppguide.html#Use_of_const
In v1.6.0, compiler support for const became a requirement.
It should be used consistently. To maintain backwards compatibility,
PNG_CONST is still maintained in deprecated form.
In v1.6.0, size_t became a required type. It should be used
consistently. To maintain backwards compatibility, png_size_t
is still maintained in deprecated form.
