From: Andy Lutomirski <email@example.com> To: Kees Cook <firstname.lastname@example.org> Cc: ksummit <email@example.com>, Andy Lutomirski <firstname.lastname@example.org> Subject: Re: [Ksummit-discuss] [TECH TOPIC] seccomp Date: Thu, 15 Aug 2019 11:26:10 -0700 Message-ID: <CALCETrV+tk9irkoRTQCk+Ve37kce3V+7M1rFWwoDD8YqZS3p7Q@mail.gmail.com> (raw) In-Reply-To: <201908151034.CC0F7BD84@keescook> On Thu, Aug 15, 2019 at 10:48 AM Kees Cook <email@example.com> wrote: > > On Wed, Aug 14, 2019 at 10:54:49AM -0700, Andy Lutomirski wrote: > > After thinking about this a bit more, I think that deferring the main > > seccomp filter invocation until arguments have been read is too > > problematic. It has the ordering issues you're thinking of, but it > > also has unpleasant effects if one of the reads faults or if > > SECCOMP_RET_TRACE or SECCOMP_RET_TRAP is used. I'm thinking that this > > Right, I was actually thinking of the trace/trap as being the race. > > > type of deeper inspection filter should just be a totally separate > > layer. Once the main seccomp logic decides that a filterable syscall > > will be issued then, assuming that no -EFAULT happens, a totally > > different program should get run with access to arguments. And there > > should be a way for the main program to know that the syscall nr in > > question is filterable on the running kernel. > > Right -- this is how I designed the original prototype: it was > effectively an LSM that was triggered by seccomp (since LSMs don't know > anything about syscalls -- their hooks are more generalized). So seccomp > would set a flag to make the LSM hook pay attention. > > Existing LSMs are system-owner defined, so really something like Landlock > is needed for a process-owned LSM to be defined. But I worry that LSM > hooks are still too "deep" in the kernel to have a process-oriented > filter author who is not a kernel developer make any sense of the > hooks. They're certainly oriented in a better position to gain the > intent of a filter. For example, if a filter says "you can't open(2) > /etc/foo", but it misses saying "you can't openat(2) /etc/foo", that's a > dumb exposure. The LSM hooks are positioned to say "you can't manipulate > /etc/foo through any means". > > So, I'm not entirely sure. It needs a clear design that chooses and > justifies the appropriate "depth" of filtering. And FWIW, the two most > frequent examples of argument parsing requests have been path-based > checking and network address checking. So any prototype needs to handle > these two cases sanely... > But also clone() flag filtering, and new clone() proposals keep wanting to add structs. And filtering bpf(). /me runs. But yes, doing this LSM-style could also make sense.
next prev parent reply index Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-07-19 9:35 Christian Brauner 2019-07-19 12:32 ` Andy Lutomirski 2019-07-20 3:18 ` Kees Cook 2019-08-14 17:54 ` Andy Lutomirski 2019-08-15 17:48 ` Kees Cook 2019-08-15 18:26 ` Andy Lutomirski [this message] 2019-08-15 18:31 ` Christian Brauner 2019-08-15 19:21 ` Andy Lutomirski 2019-07-20 7:23 ` James Morris 2019-07-20 7:41 ` Christian Brauner 2019-07-25 14:18 ` Serge E. Hallyn
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