Say you wanted to give web users a boost::regex interface to a set of data, knowing that some will try to use it for mischief and malice. I'm vaguely aware that one can write a regex to consume lots of CPU (denial-of-service attack), but also lots of stack and/or memory.
Boost.Regex has two protections against that:
* When BOOST_REGEX_NON_RECURSIVE is defined (the default for all current compilers) then memory usage is strictly limited. This can be configured in boost/regex/user.hpp since the maximum amount of memory used is BOOST_REGEX_MAX_BLOCKS*BOOST_REGEX_BLOCKSIZE, which defaults to 4Mb in total. * The total number of machine states visited (and hence CPU time consumed) is controlled by perl_matcher::estimate_max_state_count, the macro BOOST_REGEX_MAX_STATE_COUNT sets an upper limit on the number of states visited.
Thanks, John and Eric.
So if one deliberately sets the values BOOST_REGEX_MAX_BLOCKS, BOOST_REGEX_BLOCKSIZE, and BOOST_REGEX_MAX_STATE_COUNT, and catches the exceptions thrown, it ought to be ok?
Yep, but note that those macros have sensible defaults already.
And, by the way, the exceptions thrown would be std::bad_alloc, std::runtime_error, or boost::regex_error (from the regex FAQ). Does that cover them? (I know a catch (...) wouldn't hurt...)
I believe so yes, ultimately anything that's ever thrown will inherit from std::exception anyway. John.