On November 16, 2021 1:23 PM, Taylor Blau wrote: > On Tue, Nov 16, 2021 at 11:01:20AM -0500, rsbecker@xxxxxxxxxxxxx wrote: > > On November 16, 2021 10:31 AM, Jeff King wrote: > > > On Tue, Nov 16, 2021 at 03:35:41AM +0000, brian m. carlson wrote: > > > > > > > The order of options is also important here. On systems with > > > > arc4random, which is most of the BSDs, we use that, since, except > > > > on MirBSD, it uses ChaCha20, which is extremely fast, and sits > > > > entirely in userspace, avoiding a system call. We then prefer > > > > getrandom over getentropy, because the former has been available > > > > longer on Linux, and finally, if none of those are available, we > > > > use /dev/urandom, because most Unix-like operating systems provide > > > > that API. We prefer options that don't involve device files when > > > > possible because those work in some restricted environments where > device files may not be available. > > > > > > I wonder if we'll need a low-quality fallback for older systems > > > which don't even have /dev/urandom. Because it's going to be used in > > > such a core part of the system (tempfiles), this basically becomes a > > > hard requirement for using Git at all. > > > > > > I can't say I'm excited in general to be introducing a dependency > > > like this, just because of the portability headaches. But it may be > > > the least bad thing (especially if we can fall back to the existing behavior). > > > One alternative would be to build on top of the system mkstemp(), > > > which makes it libc's problem. I'm not sure if we'd run into problems > there, though. > > > > None of /dev/urandom, /dev/random, or mkstemp are available on some > > platforms, including NonStop. This is not a good dependency to add. > > One variant PRNGD is used in ia64 OpenSSL, while the CPU random > > generator in hardware is used on x86. I cannot get behind this at all. > > Libc is also not used in or available to our port. I am very worried > > about this direction. > > I share Peff's lack of enthusiasm about the dependency situation. But making > Git depend on having /dev/urandom available is simply not feasible, as you > point out. > > I wonder if the suitable fall-back should be the existing behavior of > git_mkstemps_mode()? That leaves us in a somewhat-disappointing > situation of not having fully resolved the DOS attack on all platforms. > But it makes our dependency situation less complicated, and leaves things no > worse off than the were before on platforms like NonStop. The general advice on NonStop is to delegate handling DOS attacks to either SSH or firewalls (preferably). I have yet to see anyone publish a git service on that platform outside of using SSH anyway - and if they did, they would get a pretty fierce glare from me. -Randall
