On Mon, Mar 02, 2020 at 01:09:06PM +0100, Florian Weimer wrote: > * Christian Brauner: > > >> But that's inconsistent with the rest of the system. And for example, > >> if you make /etc/resolv.conf a symbolic link, a program which uses a new > >> I/O library (with the new interfaces) will not be able to read it. > > > > Fair, but I expect that e.g. a C library would simply implement openat() > > on top of openat2() if the latter is available and thus could simply > > pass RESOLVE_SYMLINKS so any new I/O library not making use of the > > syscall directly would simply get the old behavior. For anyone using the > > syscall directly they need to know about its exact semantics anyway. But > > again, maybe just having it opt-in is fine. > > I'm more worried about fancy new libraries which go directly to the new > system calls, but set the wrong defaults for a general-purpose open > operation. > > Can we pass RESOLVE_SYMLINKS with O_NOFLLOW, so that we can easily > implement open/openat for architectures that provide only the openat2 > system call? You can currently do RESOLVE_NO_SYMLINKS | O_NOFOLLOW. So I'd expect RESOLVE_SYMLINKS | O_NOFOLLOW would work as well. But from what it looks like having no symlink resolution be opt-in seems more likely. > > >> AT_SYMLINK_NOFOLLOW only applies to the last pathname component anyway, > >> so it's relatively little protection. > > > > So this is partially why I think it's at least worth considerings: the > > new RESOLVE_NO_SYMLINKS flag does block all symlink resolution, not just > > for the last component in contrast to AT_SYMLINK_NOFOLLOW. This is > > 278121417a72d87fb29dd8c48801f80821e8f75a > > RESOLVE_NO_SYMLINKS shouldn't be the default, though (whoever is > responsible for applying that default). Otherwise system administrators > can no longer move around data between different file systems and set > symbolic links accordingly. Ok, maybe then we'll just leave RESOLVE_NO_SYMLINKS as opt-in.
