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@xxxxxxxxxx>
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.
