linux-kernel - Re: [PATCH RFC v2 net-next 07/16] bpf: add lookup/update/delete/iterate methods to BPF maps

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Date:	Wed, 23 Jul 2014 14:22:24 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux API <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v2 net-next 07/16] bpf: add lookup/update/delete/iterate
 methods to BPF maps

On Wed, Jul 23, 2014 at 1:25 PM, Kees Cook <keescook@...omium.org> wrote:
> On Wed, Jul 23, 2014 at 12:49 PM, Alexei Starovoitov <ast@...mgrid.com> wrote:
>> On Wed, Jul 23, 2014 at 11:25 AM, Kees Cook <keescook@...omium.org> wrote:
>>>> +
>>>> +       /* lookup key in a given map referenced by map_id
>>>> +        * err = bpf_map_lookup_elem(int map_id, void *key, void *value)
>>>
>>> This needs map_id documentation updates too?
>>
>> yes. will grep for it just to make sure.
>>
>>>> +static int get_map_id(struct fd f)
>>>> +{
>>>> +       struct bpf_map *map;
>>>> +
>>>> +       if (!f.file)
>>>> +               return -EBADF;
>>>> +
>>>> +       if (f.file->f_op != &bpf_map_fops) {
>>>> +               fdput(f);
>>>
>>> It feels weird to me to do the fdput inside this function. Instead,
>>> should map_lookup_elem get a "err_put" label, instead?
>>
>> I don't think it will work, since I'm not sure that fd.flags will be zero
>> when fd.file == NULL. It looks so by analyzing return code path
>> in fs/file.c, but I wasn't sure that I followed all code paths,
>> so I just picked this style from fs/timerfd.c assuming it was
>> done this away on purpose and there can be the case where
>> fd.file == null and fd.flags !=0. In such case we cannot call fdput().
>
> Yeah, hm, looking around, this does seem to be the case. I guess the
> thought is that when get_map_id fails, struct fd has been handled.

correct.

> Maybe add a comment above that function as a reminder?

yes. will do.
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