While taking an EnVar as the parameter is more clear it has the
disadvantage, that passing anything outside of the range of the
enumeration is undefined behavior. The compiler could then optimize
the range check in getEnv away (perfectly legal due to UB), leading
to buffer overreads.
This function was creating a lot of new pointers and strings without
properly checking the array bounds. This commit adds several calls
to enforce(), making sure that the pointers stay within bounds.
Strings are now created using the helper function
string_from_unterminated() to prevent overreads in the constructor of
std::string.
This fixes#400
EXV_WARN_UNUSED_RESULT is a conditional macro that expands to either
__attribute__((warn_unused_result)) on gcc & clang or to _Check_return
for MSVC
=> Compiler warns if the return value is ignored
in the following call:
getHeaderOffset (payload.pData_, payload.size_, (byte*)&exifLongHeader, 6);
getHeaderOffset would read 6 bytes from exifLongHeader, reading beyond the
bounds of the array => add 2 padding bytes to prevent overreads
memcmp() compares the read data from key with the provided string, but when
key.pData_ is shorter than the provided length, then memcmp can read beyond the
bounds of key.pData_
=> add custom compare function, which ensures that we never read more than
key.size_
The pointer p is advanced in the while loop to step over three '\n'.
However, its length is never reduced accordingly. => the length check in the
following for loop is invalid, as it permits overreading by the number of
characters that p was advanced by.
The loop condition will perform a range check correctly, but it will always
dereference bytes[i], even if i is too large and fails the second check.
=> move the bytes[i] == 0x1c check into a if, after the range check was
successfull
Luis Díaz Más
Robin Mills
Dan Čermák
Hombre