Messages in this thread | | | Date | Fri, 29 Apr 2022 11:20:46 -0700 | From | Kees Cook <> | Subject | Re: [PATCH v3 1/2] seccomp: Add wait_killable semantic to seccomp user notifier |
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On Fri, Apr 29, 2022 at 05:14:37PM +0000, Sargun Dhillon wrote: > On Fri, Apr 29, 2022 at 11:42:15AM +0200, Rodrigo Campos wrote: > > On Fri, Apr 29, 2022 at 4:32 AM Sargun Dhillon <sargun@sargun.me> wrote: > > > the concept is searchable. If the notifying process is signaled prior > > > to the notification being received by the userspace agent, it will > > > be handled as normal. > > > > Why is that? Why not always handle in the same way (if wait killable > > is set, wait like that) > > > > The goal is to avoid two things: > 1. Unncessary work - Often times, we see workloads that implement techniques > like hedging (Also known as request racing[1]). In fact, RFC3484 > (destination address selection) gets implemented where the DNS library > will connect to many backend addresses and whichever one comes back first > "wins". > 2. Side effects - We don't want a situation where a syscall is in progress > that is non-trivial to rollback (mount), and from user space's perspective > this syscall never completed. > > Blocking before the syscall even starts is excessive. When we looked at this > we found that with runtimes like Golang, they can get into a bad situation > if they have many (1000s) of threads that are in the middle of a syscall > because all of them need to elide prior to GC. In this case the runtime > prioritizes the liveness of GC vs. the syscalls. > > That being said, there may be some syscalls in a filter that need the suggested > behaviour. I can imagine introducing a new flag > (say SECCOMP_FILTER_FLAG_WAIT_KILLABLE) that applies to all states. > Alternatively, in one implementation, I put the behaviour in the data > field of the return from the BPF filter.
I'd add something like the above to the commit log, just to have it around.
-- Kees Cook
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