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Subject: Re: [PATCH bpf-next] bpf: fix flags check in
 bpf_percpu_cgroup_storage_update()
To:     Roman Gushchin <guro@fb.com>, netdev@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, kernel-team@fb.com,
        Alexei Starovoitov <ast@kernel.org>
References: <20180928110648.22973-1-guro@fb.com>
From:   Daniel Borkmann <daniel@iogearbox.net>
Message-ID: <c093c1ec-2da4-59ef-4617-f494b48952f0@iogearbox.net>
Date:   Fri, 28 Sep 2018 14:11:48 +0200
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On 09/28/2018 01:06 PM, Roman Gushchin wrote:
> Fix an issue in bpf_percpu_cgroup_storage_update(): it should return
> -EINVAL on an attempt to pass BPF_NOEXIST rather than BPF_EXIST.
> 
> Cgroup local storage is automatically created on attaching of a bpf
> program to a cgroup, and it can't be done from the userspace.
> 
> Fixes: 0daef9b42374 ("bpf: introduce per-cpu cgroup local storage")
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Alexei Starovoitov <ast@kernel.org>
> ---
>  kernel/bpf/local_storage.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c
> index c739f6dcc3c2..190535f6d5e2 100644
> --- a/kernel/bpf/local_storage.c
> +++ b/kernel/bpf/local_storage.c
> @@ -191,7 +191,7 @@ int bpf_percpu_cgroup_storage_update(struct bpf_map *_map, void *_key,
>  	int cpu, off = 0;
>  	u32 size;
>  
> -	if (unlikely(map_flags & BPF_EXIST))
> +	if (map_flags & BPF_NOEXIST)
>  		return -EINVAL;

Hmm, this is also incorrect as any future reserved flag would be accepted here and
couldn't be extended anymore. :/ And it looks like cgroup_storage_update_elem() is
doing the same today, given the cgroups local storage is still early, we should route
a patch to stable for fixing this.

Wrt this series, given the series is top of tree right now, I would prefer a fresh
respin so we have the fix integrated properly w/o follow-up. Perhaps this could also
incorporate Alexei's previous cleanup suggestions as well from today if you have a
chance.

Thanks,
Daniel