linux-kernel - Re: [PATCH bpf-next v2 0/2] Fix cgroup attach flags being assigned to effective progs

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Message-ID: <YxomJlABk3fzQ9bQ@google.com>
Date:   Thu, 8 Sep 2022 10:28:06 -0700
From:   sdf@...gle.com
To:     Pu Lehui <pulehui@...weicloud.com>
Cc:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Quentin Monnet <quentin@...valent.com>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
        Jiri Olsa <jolsa@...nel.org>, Pu Lehui <pulehui@...wei.com>
Subject: Re: [PATCH bpf-next v2 0/2] Fix cgroup attach flags being assigned to
 effective progs

On 09/08, Pu Lehui wrote:
> From: Pu Lehui <pulehui@...wei.com>

> When root-cgroup attach multi progs and sub-cgroup attach a
> override prog, bpftool will display incorrectly for the attach
> flags of the sub-cgroup’s effective progs:

> $ bpftool cgroup tree /sys/fs/cgroup effective
> CgroupPath
> ID       AttachType      AttachFlags     Name
> /sys/fs/cgroup
> 6        cgroup_sysctl   multi           sysctl_tcp_mem
> 13       cgroup_sysctl   multi           sysctl_tcp_mem
> /sys/fs/cgroup/cg1
> 20       cgroup_sysctl   override        sysctl_tcp_mem
> 6        cgroup_sysctl   override        sysctl_tcp_mem <- wrong
> 13       cgroup_sysctl   override        sysctl_tcp_mem <- wrong
> /sys/fs/cgroup/cg1/cg2
> 20       cgroup_sysctl                   sysctl_tcp_mem
> 6        cgroup_sysctl                   sysctl_tcp_mem
> 13       cgroup_sysctl                   sysctl_tcp_mem

> For cg1, obviously, the attach flags of prog6 and prog13 can not be
> OVERRIDE, and the attach flags of prog6 and prog13 is meaningless for
> cg1. We only need to care the attach flags of prog which attached to
> cg1, other progs attach flags should be omit. After these patches,
> the above situation will show as bellow:

> $ bpftool cgroup tree /sys/fs/cgroup effective
> CgroupPath
> ID       AttachType      AttachFlags     Name
> /sys/fs/cgroup
> 6        cgroup_sysctl   multi           sysctl_tcp_mem
> 13       cgroup_sysctl   multi           sysctl_tcp_mem
> /sys/fs/cgroup/cg1
> 20       cgroup_sysctl   override        sysctl_tcp_mem
> 6        cgroup_sysctl                   sysctl_tcp_mem
> 13       cgroup_sysctl                   sysctl_tcp_mem
> /sys/fs/cgroup/cg1/cg2
> 20       cgroup_sysctl                   sysctl_tcp_mem
> 6        cgroup_sysctl                   sysctl_tcp_mem
> 13       cgroup_sysctl                   sysctl_tcp_mem

> v2:
> - Limit prog_cnt to avoid overflow. (John)
> - Add more detail message.

John also raised a good question in v1: the flags don't seem to
make sense when requesting effective list. So maybe not export them
at all?

> v1:
> https://lore.kernel.org/bpf/20220820120234.2121044-1-pulehui@huawei.com

> Pu Lehui (2):
>    bpf, cgroup: Fix attach flags being assigned to effective progs
>    bpftool: Fix cgroup attach flags being assigned to effective progs

>   kernel/bpf/cgroup.c        | 5 ++++-
>   tools/bpf/bpftool/cgroup.c | 9 +++------
>   2 files changed, 7 insertions(+), 7 deletions(-)

> --
> 2.25.1