linux-kernel - Re: [PATCH 2/3] bpf: Remove dead variable

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Message-ID: <59E50473.7040609@iogearbox.net>
Date:   Mon, 16 Oct 2017 21:11:47 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Richard Weinberger <richard@....at>
CC:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        ast@...nel.org
Subject: Re: [PATCH 2/3] bpf: Remove dead variable

On 10/16/2017 08:59 PM, Richard Weinberger wrote:
> Am Montag, 16. Oktober 2017, 20:54:36 CEST schrieb Daniel Borkmann:
>> On 10/16/2017 08:18 PM, Richard Weinberger wrote:
>>> task is never used in bpf_get_current_uid_gid(), kill it.
>>>
>>> Signed-off-by: Richard Weinberger <richard@....at>
>>> ---
>>>
>>>    kernel/bpf/helpers.c | 1 -
>>>    1 file changed, 1 deletion(-)
>>>
>>> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
>>> index e8845adcd15e..511c9d522cfc 100644
>>> --- a/kernel/bpf/helpers.c
>>> +++ b/kernel/bpf/helpers.c
>>> @@ -131,7 +131,6 @@ const struct bpf_func_proto
>>> bpf_get_current_pid_tgid_proto = {>
>>>    BPF_CALL_0(bpf_get_current_uid_gid)
>>>    {
>>>
>>> -	struct task_struct *task = current;
>>>
>>>    	kuid_t uid;
>>>    	kgid_t gid;
>>
>> Needs to be squashed into patch 1/3?
>
> I can squash it into 1/3, I kept it that way because
> even without 1/3 this variable is unused.

Hmm, the helper looks like the below. In patch 1/3 you removed
the 'if (unlikely(!task))' test where the variable was used before,
so 2/3 without the 1/3 would result in a compile error.

BPF_CALL_0(bpf_get_current_uid_gid)
{
	struct task_struct *task = current;
	kuid_t uid;
	kgid_t gid;

	if (unlikely(!task))
		return -EINVAL;

	current_uid_gid(&uid, &gid);
	return (u64) from_kgid(&init_user_ns, gid) << 32 |
		     from_kuid(&init_user_ns, uid);
}