[PATCH bpf 1/3] bpf: Report BPF_F_PREORDER in cgroup program queries

[Hui Su]

Commit 4b82b181a26c ("bpf: Allow pre-ordering for bpf cgroup progs")
introduced BPF_F_PREORDER to request pre-order execution across the
cgroup hierarchy, altering the effective prog array ordering.

While pl->flags stores BPF_F_PREORDER for each attached program,
__cgroup_bpf_query() currently fails to report it. When querying
attached programs (!effective_query), __cgroup_bpf_query() fills
prog_attach_flags[] with cgrp->bpf.flags[atype] for all entries,
omitting the per-program BPF_F_PREORDER attribute.

As a result, user space tools and query callers cannot distinguish
pre-ordered programs from standard multi-prog attachments via
BPF_PROG_QUERY.

Fix this by merging (pl->flags & BPF_F_PREORDER) with the cgroup-wide
flags when copying prog_attach_flags to user space. Only BPF_F_PREORDER
is extracted from pl->flags to ensure transient positioning flags (such
as BPF_F_BEFORE, BPF_F_AFTER, BPF_F_ID, or BPF_F_REPLACE) are not
leaked to user space. Also perform both ID and attach flags copies
within the same hlist iteration.

Fixes: 4b82b181a26c ("bpf: Allow pre-ordering for bpf cgroup progs")
Signed-off-by: Hui Su <sh_def@xxxxxxx>
---
 kernel/bpf/cgroup.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 149672c76c49..e7c7efa1baa7 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -1353,19 +1353,19 @@ static int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
 				id = prog->aux->id;
 				if (copy_to_user(prog_ids + i, &id, sizeof(id)))
 					return -EFAULT;
+				if (prog_attach_flags) {
+					flags = cgrp->bpf.flags[atype] |
+						(pl->flags & BPF_F_PREORDER);
+					if (copy_to_user(prog_attach_flags + i,
+							 &flags, sizeof(flags)))
+						return -EFAULT;
+				}
 				if (++i == cnt)
 					break;
 			}
 
-			if (prog_attach_flags) {
-				flags = cgrp->bpf.flags[atype];
-
-				for (i = 0; i < cnt; i++)
-					if (copy_to_user(prog_attach_flags + i,
-							 &flags, sizeof(flags)))
-						return -EFAULT;
+			if (prog_attach_flags)
 				prog_attach_flags += cnt;
-			}
 		}
 
 		prog_ids += cnt;
-- 
2.55.0