Messages in this thread | | | Date | Thu, 10 Mar 2022 18:44:33 +0100 | From | Domenico Andreoli <> | Subject | Re: [PATCH] binfmt_misc: add two-steps registration (opt-in) |
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On Thu, Mar 10, 2022 at 08:13:25AM -0800, Kees Cook wrote: > On Tue, Mar 01, 2022 at 02:28:22PM +0100, Domenico Andreoli wrote: > > From: Domenico Andreoli <domenico.andreoli@linux.com> > > > > Experimenting with new interpreter configurations can lead to annoying > > failures, when the system is left unable to load ELF binaries power > > cycling is the only way to get it back operational. > > > > This patch tries to mitigate such conditions by adding an opt-in > > two-steps registration. > > > > A new optional field is added to the configuration string, it's an > > expiration interval for the newly added interpreter. If the user is > > not able to confirm in time, possibly because the system is broken, > > the new interpreter is automatically disabled. > > Hi!
Hi!
> > As this both changes the userspace API and adds timers, I'd like the
Right but 1. it's backward compatible, 2. it fails on unsupporting kernels.
Curiosity, I understand why API changes require care but what's so special about the timers?
> change to be really well justified. Can you explain the conditions you > get into that can't be escaped by just disabling the bad binfmt_misc > entry?
It happened when I somehow messed up with the ELF loader of my system, it was the very first time I tried to manually configure qemu-user-static for a foreign architecture.
Suddenly I could not do anything, no ls, no cat. Did not realize that my shell has built-in echo and that I could cut-and-paste the path for disabling the bad interpreter. I did not investigate what I did wrong or what I could do better, I simply didn't do it again.
I just got a deeper understanding of the note in Debian's update-binfmts manpage:
If you're not careful, you can break your system with update-binfmts. An easy way to do this is to register an ELF binary as a handler for ELF, which will almost certainly cause your system to hang immediately; even if it doesn't, you won't be able to run update-binfmts to fix it.
I shot on my foot and I thought the API could be made a bit more friendly.
Thanks, Dom
> > -Kees > > -- > Kees Cook
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