On Thu, May 18, 2023 at 09:25:08AM -0700, Alexei Starovoitov wrote: > We're still talking past each other. > 0 is an invalid bpf object. Not file. > There is a difference. > The kernel is breaking user space by returning non-file FDs in 0,1,2. > Especially as fd = 1 and 2. > ensure_good_fd() in libbpf is a library workaround to make sure bpf objects > are not the reason for user app brekage. > I firmly believe that making kernel return socket FDs and other special FDs with fd >=3 > (under new sysctl, for example) will prevent user space breakage. Wait, why are socket FDs special? I shouldn't be able to have anything but chardev fds, pipes and regular files as fd 0,1,2? I agree that having directory fds and blockdev fds as fd 0,1,2 are confusing and pointless, but I see the value in having a TCP socket as stdin/stdout/stderr. If a fd shouldn't be used for stdio, having an ioctl to enable it and read/write return errors until/unless it's enabled makes sense. But now we have to label each fd as safe/not-safe for stdio, which we can as easily do by setting up our fops appropriately. So I'm not sure what you're trying to accomplish here.
