[PATCH bpf-next v2 1/3] bpf: Report BPF_F_PREORDER in cgroup program queries

[Hui Su <sh_def@163.com>]

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 does not 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.

Extend direct cgroup program queries to merge (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.

This extends prog_attach_flags[] with the per-program BPF_F_PREORDER bit.
This can introduce new prog_attach_flags[] values with BPF_F_PREORDER set,
for example 0x40 (BPF_F_PREORDER), 0x41 (BPF_F_ALLOW_OVERRIDE |
BPF_F_PREORDER), or 0x42 (BPF_F_ALLOW_MULTI | BPF_F_PREORDER) depending
on the cgroup-wide attachment mode.

Older bpftool versions treat such combinations as unknown flags; bpftool
support is updated later in this series.

Signed-off-by: Hui Su <sh_def@163.com>
---
 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 696b27383974..eb9e0985ac43 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -1515,19 +1515,19 @@ static int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
 				id = prog_list_id(pl);
 				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