On 02/10/2017 06:08 PM, Kees Cook wrote: > On Fri, Feb 10, 2017 at 4:01 PM, Tyler Hicks <tyhi...@canonical.com> wrote: >> On 02/07/2017 06:33 PM, Kees Cook wrote: >>> This adds to UAPI, so it'd be good to think for a moment about how >>> this would work on older kernels: right now, if someone tried to use >>> this RET_LOG on an old kernel, it'll get treated like RET_KILL. Is >>> this sane? >> >> It is not sane for userspace code to blindly attempt to use a new >> feature on an old kernel. One of the main motivations of the >> actions_avail sysctl is to allow userspace to be smart about what the >> current kernel supports. > > Yeah, agreed. I mean, userspace could also build a little test > program, toss in RET_LOG, run it and see if it get SIGSYS. But that's > so much more pain that checking in /proc. > >> I'll be adding logic (requested by Paul) to libseccomp that checks this >> sysctl when SECOMP_RET_LOG is attempted to be used. Programs that don't >> use libseccomp will have to do something similar. > > Excellent, I had been meaning to ask if you'd chatted with Paul at > all, since this is an API addition for libseccomp.
We talked through some of it after the initial PR that I submitted to libseccomp: https://github.com/seccomp/libseccomp/pull/64 I'll be updating that as we get closer to a land-able set of kernel patches. > Speaking of which, can you CC linux-api@ on the next version too? Yes, good idea! Tyler
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