linux-kernel - Re: 答复: [PATCH bpf-next] samples/bpf: check detach prog exist or not in xdp

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Message-ID: <87h75zynz2.fsf@toke.dk>
Date:   Mon, 09 May 2022 12:55:29 +0200
From:   Toke Høiland-Jørgensen <toke@...nel.org>
To:     shaozhengchao <shaozhengchao@...wei.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "hawk@...nel.org" <hawk@...nel.org>,
        "john.fastabend@...il.com" <john.fastabend@...il.com>,
        "andrii@...nel.org" <andrii@...nel.org>,
        "kafai@...com" <kafai@...com>,
        "songliubraving@...com" <songliubraving@...com>,
        "yhs@...com" <yhs@...com>,
        "kpsingh@...nel.org" <kpsingh@...nel.org>
Cc:     "weiyongjun (A)" <weiyongjun1@...wei.com>,
        yuehaibing <yuehaibing@...wei.com>
Subject: Re: 答复: [PATCH bpf-next] samples/bpf: check
 detach prog exist or
 not in xdp_fwd

shaozhengchao <shaozhengchao@...wei.com> writes:

> -----邮件原件-----
> 发件人: Toke Høiland-Jørgensen [mailto:toke@...nel.org] 
> 发送时间: 2022年5月9日 17:46
> 收件人: shaozhengchao <shaozhengchao@...wei.com>; bpf@...r.kernel.org; netdev@...r.kernel.org; linux-kernel@...r.kernel.org; ast@...nel.org; daniel@...earbox.net; davem@...emloft.net; kuba@...nel.org; hawk@...nel.org; john.fastabend@...il.com; andrii@...nel.org; kafai@...com; songliubraving@...com; yhs@...com; kpsingh@...nel.org
> 抄送: weiyongjun (A) <weiyongjun1@...wei.com>; shaozhengchao <shaozhengchao@...wei.com>; yuehaibing <yuehaibing@...wei.com>
> 主题: Re: [PATCH bpf-next] samples/bpf: check detach prog exist or not in xdp_fwd
>
> Zhengchao Shao <shaozhengchao@...wei.com> writes:
>
>> Before detach the prog, we should check detach prog exist or not.
>
> If we're adding such a check we should also check that it's the *right* program. I.e., query the ID for the program name and check that it matches what the program attached, then obtain an fd and pass that as XDP_EXPECTED_FD on detach to make sure it wasn't swapped out in the meantime...
>
> -Toke
>
> Thank you for your reply. When finish running xdp_fwd to attatch prog,
> the program will exit and can't store fd as XDP_EXPECTED_FD.
>
> I think the sample xdp_fwd -d is just detach prog and don't care if
> the fd is expected.

So why are you adding the check? Either keep it the way it is, or add a
proper check that examines the program type; you're right that it
doesn't store the prog FD, but you can still check the program name and
see if it matches to get some idea that it's not a totally separate
program that's loaded. I think doing so would be an improvement to the
sample, but just adding a check if a program is loaded is not, really...

-Toke