Messages in this thread | | | Date | Mon, 19 Sep 2022 10:28:25 -0700 | Subject | Re: [PATCH bpf-next v3 1/2] bpf, cgroup: Don't populate prog_attach_flags array when effective query | From | Martin KaFai Lau <> |
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On 9/19/22 6:32 AM, Pu Lehui wrote: > > > On 2022/9/17 8:03, Martin KaFai Lau wrote: >> On 9/14/22 9:17 AM, Pu Lehui wrote: >>> From: Pu Lehui <pulehui@huawei.com> >>> >>> Attach flags is only valid for attached progs of this layer cgroup, >>> but not for effective progs. For querying with EFFECTIVE flags, >>> exporting attach flags does not make sense. so we don't need to >>> populate prog_attach_flags array when effective query. >> >> prog_attach_flags has been added to 6.0 which is in rc5. It is still >> doable (and cleaner) to reject prog_attach_flags when it is an >> effective_query. This should be done regardless of 'type == >> BPF_LSM_CGROUP' or not. Something like: >> >> if (effective_query && prog_attach_flags) >> return -EINVAL; >> >> Otherwise, the whole prog_attach_flags needs to be set to 0 during >> effective_query. Please target the change to the bpf tree instead of >> bpf-next such that this uapi bit can be fixed before 6.0. >> > > Okay, will handle in next version.
Thanks. It will also be useful to comment the uapi's bpf.h and mention prog_attach_flags should not be set during effective_query.
> >> Also, the effective_query issue is not limited to the >> prog_attach_flags? For the older uattr->query.attach_flags, it should >> be set to 0 also when it is an effective_query, right? > > For output uattr->query.attach_flags, we certainly don't need to copy it > to userspace when effective query. Since we do not utilize > uattr->query.attach_flags in the cgroup query function, should we need > to take it as input and reject when it is non-zero in effective query? > Something like: > if (effective_query && (prog_attach_flags || attr->query.attach_flags))
No. I don't think the zero attr->query.attach_flags can be enforced now. It is used as an output value only and its input value has never been checked. Although the bpftool always sets it to 0 before the query, checking zero now does not gain much while there is a slight chance of breaking other users.
Only need to set/output uattr->query.attach_flags as 0 during effective_query.
> > For both output and input scenarios, we are faced with the problem that > there is a ambiguity in attach_flags being 0. When we do not copy to the > userspace, libbpf will set it to 0 by default, and 0 can mean NONE flag > attach, or no attach prog. The same is true for input scenarios. > > So should we need to define NONE attach flag and redefine the others? > Such as follow: > #define BPF_F_ALLOW_NONE (1U << 0)
I would not change the uapi for this. 0 implicitly means no flags or none. Regardless, this change does not belong to the bpf tree where this fix will be landing.
> #define BPF_F_ALLOW_OVERRIDE (1U << 1) > #define BPF_F_ALLOW_MULTI (1U << 2) > #define BPF_F_REPLACE (1U << 3) > > And then attach flags being 0 certainly means no attach any prog. >
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