[PATCH bpf-next v4 10/15] bpf: Allow all struct_ops to use bpf_dynptr_from_skb()

[Amery Hung <ameryhung@gmail.com>]

bpf_dynptr_from_skb() was only made available to bpf_qdisc, so far the
only struct_ops type that needs to read an skb. The upcoming bpf_tcp_ops
header-option hooks (parse_hdr/write_hdr_opt) also want to access the TCP
options of an skb through a dynptr.

All struct_ops programs share BPF_PROG_TYPE_STRUCT_OPS, so register
bpf_kfunc_set_skb (which holds bpf_dynptr_from_skb) for that program type
once, instead of per struct_ops. This makes bpf_dynptr_from_skb()
available to bpf_tcp_ops and any future struct_ops.

With the kfunc now provided to all of struct_ops, the bpf_qdisc-specific
registration becomes redundant and is dropped: bpf_qdisc_kfunc_filter()
only constrains kfuncs listed in qdisc_kfunc_ids, so removing
bpf_dynptr_from_skb from that set (and from qdisc_common_kfunc_set) lets
it fall through the filter unchanged, and bpf_qdisc keeps access via the
generic struct_ops registration.

Widening the registration is safe: a struct_ops that does not receive an
skb in its context has nothing to pass to the helper.

Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Amery Hung <ameryhung@gmail.com>
---
 net/core/filter.c     | 1 +
 net/sched/bpf_qdisc.c | 2 --
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 61940e753552..47b7a8f73069 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -12887,6 +12887,7 @@ static int __init bpf_kfunc_init(void)
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_SEG6LOCAL, &bpf_kfunc_set_skb);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_NETFILTER, &bpf_kfunc_set_skb);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &bpf_kfunc_set_skb);
+	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &bpf_kfunc_set_skb);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &bpf_kfunc_set_skb_meta);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_ACT, &bpf_kfunc_set_skb_meta);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &bpf_kfunc_set_xdp);
diff --git a/net/sched/bpf_qdisc.c b/net/sched/bpf_qdisc.c
index 098ca02aed89..5691c13781a8 100644
--- a/net/sched/bpf_qdisc.c
+++ b/net/sched/bpf_qdisc.c
@@ -280,7 +280,6 @@ BTF_KFUNCS_START(qdisc_kfunc_ids)
 BTF_ID_FLAGS(func, bpf_skb_get_hash)
 BTF_ID_FLAGS(func, bpf_kfree_skb, KF_RELEASE)
 BTF_ID_FLAGS(func, bpf_qdisc_skb_drop, KF_RELEASE)
-BTF_ID_FLAGS(func, bpf_dynptr_from_skb)
 BTF_ID_FLAGS(func, bpf_qdisc_watchdog_schedule)
 BTF_ID_FLAGS(func, bpf_qdisc_init_prologue)
 BTF_ID_FLAGS(func, bpf_qdisc_reset_destroy_epilogue)
@@ -290,7 +289,6 @@ BTF_KFUNCS_END(qdisc_kfunc_ids)
 BTF_SET_START(qdisc_common_kfunc_set)
 BTF_ID(func, bpf_skb_get_hash)
 BTF_ID(func, bpf_kfree_skb)
-BTF_ID(func, bpf_dynptr_from_skb)
 BTF_SET_END(qdisc_common_kfunc_set)
 
 BTF_SET_START(qdisc_enqueue_kfunc_set)
-- 
2.52.0