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Subject[PATCH bpf v4 0/2] Fix wrong cgroup attach flags being assigned to effective progs
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From: Pu Lehui <pulehui@huawei.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 for query with EFFECTIVE flags, exporting attach flags
does not make sense. So let's remove the AttachFlags field and the
associated logic. After these patches, the above effective cgroup
tree will show as bellow:

# bpftool cgroup tree /sys/fs/cgroup effective
CgroupPath
ID AttachType Name
/sys/fs/cgroup
6 cgroup_sysctl sysctl_tcp_mem
13 cgroup_sysctl sysctl_tcp_mem
/sys/fs/cgroup/cg1
20 cgroup_sysctl 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

v4:
- Reject prog_attach_flags array when effective query. (Martin)
- Target to bpf tree. (Martin)

v3:
https://lore.kernel.org/bpf/20220914161742.3180731-1-pulehui@huaweicloud.com
- Don't show attach flags when effective query. (John, sdf, Martin)

v2:
https://lore.kernel.org/bpf/20220908145304.3436139-1-pulehui@huaweicloud.com
- Limit prog_cnt to avoid overflow. (John)
- Add more detail message.

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

Pu Lehui (2):
bpf, cgroup: Reject prog_attach_flags array when effective query
bpftool: Fix wrong cgroup attach flags being assigned to effective
progs

include/uapi/linux/bpf.h | 7 +++--
kernel/bpf/cgroup.c | 28 +++++++++++-------
tools/bpf/bpftool/cgroup.c | 54 ++++++++++++++++++++++++++++++----
tools/include/uapi/linux/bpf.h | 7 +++--
4 files changed, 77 insertions(+), 19 deletions(-)

--
2.25.1

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