From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>, Tejun Heo <tj@kernel.org>,
Delyan Kratunov <delyank@fb.com>, linux-mm <linux-mm@kvack.org>,
bpf <bpf@vger.kernel.org>, Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH v3 bpf-next 13/15] bpf: Prepare bpf_mem_alloc to be used by sleepable bpf programs.
Date: Fri, 19 Aug 2022 16:01:08 -0700 [thread overview]
Message-ID: <CAADnVQLXKaNsP7VuGBfnrsNwEZ2BYQYcQ=s3EGS-g6HhM9E1uA@mail.gmail.com> (raw)
In-Reply-To: <CAP01T77A1pqYQKeECDSCoxH1pQ1Vxcm84B8_D_r0xoZv_bbq_A@mail.gmail.com>
On Fri, Aug 19, 2022 at 3:56 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> On Sat, 20 Aug 2022 at 00:43, Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Sat, Aug 20, 2022 at 12:21:46AM +0200, Kumar Kartikeya Dwivedi wrote:
> > > On Fri, 19 Aug 2022 at 23:43, Alexei Starovoitov
> > > <alexei.starovoitov@gmail.com> wrote:
> > > >
> > > > From: Alexei Starovoitov <ast@kernel.org>
> > > >
> > > > Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
> > > > Then use call_rcu() to wait for normal progs to finish
> > > > and finally do free_one() on each element when freeing objects
> > > > into global memory pool.
> > > >
> > > > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> > > > ---
> > >
> > > I fear this can make OOM issues very easy to run into, because one
> > > sleepable prog that sleeps for a long period of time can hold the
> > > freeing of elements from another sleepable prog which either does not
> > > sleep often or sleeps for a very short period of time, and has a high
> > > update frequency. I'm mostly worried that unrelated sleepable programs
> > > not even using the same map will begin to affect each other.
> >
> > 'sleep for long time'? sleepable bpf prog doesn't mean that they can sleep.
> > sleepable progs can copy_from_user, but they're not allowed to waste time.
>
> It is certainly possible to waste time, but indirectly, not through
> the BPF program itself.
>
> If you have userfaultfd enabled (for unpriv users), an unprivileged
> user can trap a sleepable BPF prog (say LSM) using bpf_copy_from_user
> for as long as it wants. A similar case can be done using FUSE, IIRC.
>
> You can then say it's a problem about unprivileged users being able to
> use userfaultfd or FUSE, or we could think about fixing
> bpf_copy_from_user to return -EFAULT for this case, but it is totally
> possible right now for malicious userspace to extend the tasks trace
> gp like this for minutes (or even longer) on a system where sleepable
> BPF programs are using e.g. bpf_copy_from_user.
Well in that sense userfaultfd can keep all sorts of things
in the kernel from making progress.
But nothing to do with OOM.
There is still the max_entries limit.
The amount of objects in waiting_for_gp is guaranteed to be less
than full prealloc.
next prev parent reply other threads:[~2022-08-19 23:01 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-19 21:42 [PATCH v3 bpf-next 00/15] bpf: BPF specific memory allocator Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 01/15] bpf: Introduce any context " Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 02/15] bpf: Convert hash map to bpf_mem_alloc Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 03/15] selftests/bpf: Improve test coverage of test_maps Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 04/15] samples/bpf: Reduce syscall overhead in map_perf_test Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 05/15] bpf: Relax the requirement to use preallocated hash maps in tracing progs Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 06/15] bpf: Optimize element count in non-preallocated hash map Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 07/15] bpf: Optimize call_rcu " Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 08/15] bpf: Adjust low/high watermarks in bpf_mem_cache Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 09/15] bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU Alexei Starovoitov
2022-08-24 19:58 ` Kumar Kartikeya Dwivedi
2022-08-25 0:13 ` Alexei Starovoitov
2022-08-25 0:35 ` Joel Fernandes
2022-08-25 0:49 ` Joel Fernandes
2022-08-19 21:42 ` [PATCH v3 bpf-next 10/15] bpf: Add percpu allocation support to bpf_mem_alloc Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 11/15] bpf: Convert percpu hash map to per-cpu bpf_mem_alloc Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 12/15] bpf: Remove tracing program restriction on map types Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 13/15] bpf: Prepare bpf_mem_alloc to be used by sleepable bpf programs Alexei Starovoitov
2022-08-19 22:21 ` Kumar Kartikeya Dwivedi
2022-08-19 22:43 ` Alexei Starovoitov
2022-08-19 22:56 ` Kumar Kartikeya Dwivedi
2022-08-19 23:01 ` Alexei Starovoitov [this message]
2022-08-24 19:49 ` Kumar Kartikeya Dwivedi
2022-08-25 0:08 ` Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 14/15] bpf: Remove prealloc-only restriction for " Alexei Starovoitov
2022-08-19 21:42 ` [PATCH v3 bpf-next 15/15] bpf: Introduce sysctl kernel.bpf_force_dyn_alloc Alexei Starovoitov
2022-08-24 20:03 ` [PATCH v3 bpf-next 00/15] bpf: BPF specific memory allocator Kumar Kartikeya Dwivedi
2022-08-25 0:16 ` Alexei Starovoitov
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