Comments for getentropy_linux.c explain this http://www.openbsd.org/cgi-bin/cvsweb/src/lib/libcrypto/cryp...
We have very few options:
- Even syslog_r is unsafe to call at this low level, so there is no way to alert the user or program. - Cannot call abort() because some systems have unsafe corefiles.
This logic seems specious. It's not the job of a library to solve that problem. If a system has crash dump collection configured insecurely, the problem is going to extend well past the SSL library.
> * This can fail if the process is inside a chroot or if file * descriptors are exhausted.
The right solution is to pre-open the file descriptor. SSL_library_init can fail. Do it there.
To be fair to the LIbreSSL devs, the Linux-specific /dev/urandom code is currently encapsulated rather nicely behind an interface that's compatible with the OpenBSD getentropy() syscall. Following your suggestion would create a layer violation and move LibreSSL closer toward the (much maligned) OpenSSL approach to cross platform compatibility. I don't think this is a great excuse for the current design, but it's an explanation.
The OpenSSL approach to portability is doomed: it can only deal with cosmetic differences between platforms. I appreciate the principle of using compatibility functions instead of #ifdef, but at some point, you need to incorporate the panoply of architectures into your design. It galls me to see the OpenBSD people claim that Linux is broken merely because it is different. That's incredibly arrogance.
> This code path exists to bring light to the issue that Linux does not provide a failsafe API for entropy collection.
Trying to make a point about Linux doesn't seem like a very good reason to me.
If you were porting this to a GNU/Linux distro, you can read their list of options and raise (SIGKILL) resulting in silent termination if that's what your platform decided to do if both entropy methods fail, or test for it earlier and fail. Since they are BSD developers they leave it up to whoever is porting to decide.
Huh, FreeBSD has MAP_NOCORE which allows the program to map pages that will explicitly not be included in the core file. I never realized that this was FreeBSD-specific extension (added in 2007?).
I'm really surprised other platforms haven't adopted it, though I surmise there's a good technical reason or two. (EDIT: or maybe there's similar functionality via another API? I haven't been able to turn up anything).