[PATCH bpf-next v2] bpf, cgroup: fix cgroup struct_ops query for a second attach type

[Shakeel Butt]

Two things in __cgroup_bpf_query() work only because CGROUP_TCP_SOCK_OPS is
the only struct_ops attach type.

It calls cgroup_bpf_enabled(atype) with an atype that
find_atype_by_struct_ops_id() works out at runtime.  That macro is an asm
goto and needs a constant.  Today the compiler can see there is only one
value; add a second type and the build breaks with "impossible constraint
in 'asm'".  The check is not needed anyway.  When the key is off nothing is
attached, so progs[atype] and effective[atype] are empty and the count loop
leaves total_cnt at 0.  The other attach types already use that loop with
no such check.  Drop the check and the skip_count label.

And find_atype_by_struct_ops_id() matches on type_id alone.  An attach type
whose subsystem is not built keeps type_id 0, so a query for type 0 finds
it and returns success with nothing instead of -ENOENT.  Skip such slots.

Fixes: 369d9dcd8fb8 ("bpf: Add infrastructure to support attaching struct_ops to cgroups")
Signed-off-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Acked-by: Yafang Shao <laoar.shao@xxxxxxxxx>
Reviewed-by: Amery Hung <ameryhung@xxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
---
v2:
- Drop the cgroup_bpf_enabled() check and the skip_count label instead of
  adding cgroup_bpf_enabled_runtime() (Alexei).
- Add the bpf-next subject prefix (Amery).

v1: https://lore.kernel.org/all/20260930135159.3926039-1-shakeel.butt@xxxxxxxxx/

 kernel/bpf/cgroup.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 2bbe77de89f0..ce82963bcfc7 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -45,6 +45,7 @@ static enum cgroup_bpf_attach_type find_atype_by_struct_ops_id(u32 type_id)
 
 	for (atype = 0; atype < MAX_CGROUP_BPF_ATTACH_TYPE; atype++) {
 		if (cgroup_bpf_is_struct_ops_atype(atype) &&
+		    cgroup_struct_ops[atype].type_id &&
 		    cgroup_struct_ops[atype].type_id == type_id)
 			return atype;
 	}
@@ -1448,8 +1449,6 @@ static int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
 			return -ENOENT;
 		from_atype = to_atype = atype;
 		flags = 0;
-		if (!cgroup_bpf_enabled(atype))
-			goto skip_count;
 	} else if (type == BPF_LSM_CGROUP) {
 		if (!effective_query && attr->query.prog_cnt &&
 		    prog_ids && !prog_attach_flags)
@@ -1476,7 +1475,6 @@ static int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
 		}
 	}
 
-skip_count:
 	/* always output uattr->query.attach_flags as 0 during effective query */
 	flags = effective_query ? 0 : flags;
 	if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)))

base-commit: 6a75c73eebd4d497ded7d08b47894f9ddbebb5a9
-- 
2.53.0-Meta