linux-kernel - Re: [PATCH net-next 1/3] bpf: introduce current->pid, tgid, uid, gid, comm accessors

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Message-ID: <557B6A00.7000600@plumgrid.com>
Date:	Fri, 12 Jun 2015 16:23:44 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Wang Nan <wangnan0@...wei.com>, Li Zefan <lizefan@...wei.com>,
	Daniel Wagner <daniel.wagner@...-carit.de>,
	Daniel Borkmann <daniel@...earbox.net>,
	Linux API <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 1/3] bpf: introduce current->pid, tgid, uid,
 gid, comm accessors

On 6/12/15 3:54 PM, Andy Lutomirski wrote:
> On Fri, Jun 12, 2015 at 3:44 PM, Alexei Starovoitov <ast@...mgrid.com> wrote:
>> On 6/12/15 3:08 PM, Andy Lutomirski wrote:
>>>
>>> On Fri, Jun 12, 2015 at 2:40 PM, Alexei Starovoitov <ast@...mgrid.com>
>>> wrote:
>>>>
>>>> eBPF programs attached to kprobes need to filter based on
>>>> current->pid, uid and other fields, so introduce helper functions:
>>>>
>>>> u64 bpf_get_current_pid_tgid(void)
>>>> Return: current->tgid << 32 | current->pid
>>>>
>>>> u64 bpf_get_current_uid_gid(void)
>>>> Return: current_gid << 32 | current_uid
>>>
>>>
>>> How does this work wrt namespaces,
>>
>>
>> from_kuid(current_user_ns(), uid)
>>
>
> Is current_user_ns() well defined in the context of an eBPF program?

What do you mean 'well defined'?
Semantically same as 'current'. Depending on where particular
kprobe is placed, 'current' is either meaningful or not. Program
author needs to know what he's doing. It's a tool.

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