netdev - Re: [PATCH bpf-next] bpftool: Fix cgroup command to only show cgroup bpf programs

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Message-ID: <dcada116-20c7-45d6-8a94-8492d87f026e@iogearbox.net>
Date: Wed, 7 May 2025 23:00:40 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Martin KaFai Lau <martin.lau@...ux.dev>, bpf@...r.kernel.org
Cc: 'Alexei Starovoitov ' <ast@...nel.org>,
 'Andrii Nakryiko ' <andrii@...nel.org>, netdev@...r.kernel.org,
 kernel-team@...a.com, Quentin Monnet <qmo@...nel.org>,
 Takshak Chahande <ctakshak@...a.com>
Subject: Re: [PATCH bpf-next] bpftool: Fix cgroup command to only show cgroup
 bpf programs

On 5/7/25 10:32 PM, Martin KaFai Lau wrote:
> From: Martin KaFai Lau <martin.lau@...nel.org>
> 
> The netkit program is not a cgroup bpf program and should not be shown
> in the output of the "bpftool cgroup show" command.
> 
> However, if the netkit device happens to have ifindex 3,
> the "bpftool cgroup show" command will output the netkit
> bpf program as well:
> 
>> ip -d link show dev nk1
> 3: nk1@if2: ...
>      link/ether ...
>      netkit mode ...
> 
>> bpftool net show
> tc:
> nk1(3) netkit/peer tw_ns_nk2phy prog_id 469447
> 
>> bpftool cgroup show /sys/fs/cgroup/...
> ID       AttachType      AttachFlags     Name
> ...      ...                             ...
> 469447   netkit_peer                     tw_ns_nk2phy
> 
> The reason is that the target_fd (which is the cgroup_fd here) and
> the target_ifindex are in a union in the uapi/linux/bpf.h. The bpftool
> iterates all values in "enum bpf_attach_type" which includes
> non cgroup attach types like netkit. The cgroup_fd is usually 3 here,
> so the bug is triggered when the netkit ifindex just happens
> to be 3 as well.
> 
> The bpftool's cgroup.c already has a list of cgroup-only attach type
> defined in "cgroup_attach_types[]". This patch fixes it by iterating
> over "cgroup_attach_types[]" instead of "__MAX_BPF_ATTACH_TYPE".
> 
> Cc: Quentin Monnet <qmo@...nel.org>
> Reported-by: Takshak Chahande <ctakshak@...a.com>
> Signed-off-by: Martin KaFai Lau <martin.lau@...nel.org>

Outch, good catch!

Acked-by: Daniel Borkmann <daniel@...earbox.net>