[PATCH bpf-next v1 09/13] bpf: net_sched: Support updating qstats

[Amery Hung <amery.hung@xxxxxxxxxxxxx>]

Allow bpf qdisc programs to update Qdisc qstats directly with btf struct
access.

Signed-off-by: Amery Hung <amery.hung@xxxxxxxxxxxxx>
---
 net/sched/bpf_qdisc.c | 53 ++++++++++++++++++++++++++++++++++++-------
 1 file changed, 45 insertions(+), 8 deletions(-)

diff --git a/net/sched/bpf_qdisc.c b/net/sched/bpf_qdisc.c
index b5ac3b9923fb..3901f855effc 100644
--- a/net/sched/bpf_qdisc.c
+++ b/net/sched/bpf_qdisc.c
@@ -57,6 +57,7 @@ bpf_qdisc_get_func_proto(enum bpf_func_id func_id,
 	}
 }
 
+BTF_ID_LIST_SINGLE(bpf_qdisc_ids, struct, Qdisc)
 BTF_ID_LIST_SINGLE(bpf_sk_buff_ids, struct, sk_buff)
 BTF_ID_LIST_SINGLE(bpf_sk_buff_ptr_ids, struct, bpf_sk_buff_ptr)
 
@@ -81,20 +82,37 @@ static bool bpf_qdisc_is_valid_access(int off, int size,
 	return bpf_tracing_btf_ctx_access(off, size, type, prog, info);
 }
 
-static int bpf_qdisc_btf_struct_access(struct bpf_verifier_log *log,
-					const struct bpf_reg_state *reg,
-					int off, int size)
+static int bpf_qdisc_qdisc_access(struct bpf_verifier_log *log,
+				  const struct bpf_reg_state *reg,
+				  int off, int size)
 {
-	const struct btf_type *t, *skbt;
 	size_t end;
 
-	skbt = btf_type_by_id(reg->btf, bpf_sk_buff_ids[0]);
-	t = btf_type_by_id(reg->btf, reg->btf_id);
-	if (t != skbt) {
-		bpf_log(log, "only read is supported\n");
+	switch (off) {
+	case offsetof(struct Qdisc, qstats) ... offsetofend(struct Qdisc, qstats) - 1:
+		end = offsetofend(struct Qdisc, qstats);
+		break;
+	default:
+		bpf_log(log, "no write support to Qdisc at off %d\n", off);
+		return -EACCES;
+	}
+
+	if (off + size > end) {
+		bpf_log(log,
+			"write access at off %d with size %d beyond the member of Qdisc ended at %zu\n",
+			off, size, end);
 		return -EACCES;
 	}
 
+	return 0;
+}
+
+static int bpf_qdisc_sk_buff_access(struct bpf_verifier_log *log,
+				    const struct bpf_reg_state *reg,
+				    int off, int size)
+{
+	size_t end;
+
 	switch (off) {
 	case offsetof(struct sk_buff, tstamp):
 		end = offsetofend(struct sk_buff, tstamp);
@@ -136,6 +154,25 @@ static int bpf_qdisc_btf_struct_access(struct bpf_verifier_log *log,
 	return 0;
 }
 
+static int bpf_qdisc_btf_struct_access(struct bpf_verifier_log *log,
+				       const struct bpf_reg_state *reg,
+				       int off, int size)
+{
+	const struct btf_type *t, *skbt, *qdisct;
+
+	skbt = btf_type_by_id(reg->btf, bpf_sk_buff_ids[0]);
+	qdisct = btf_type_by_id(reg->btf, bpf_qdisc_ids[0]);
+	t = btf_type_by_id(reg->btf, reg->btf_id);
+
+	if (t == skbt)
+		return bpf_qdisc_sk_buff_access(log, reg, off, size);
+	else if (t == qdisct)
+		return bpf_qdisc_qdisc_access(log, reg, off, size);
+
+	bpf_log(log, "only read is supported\n");
+	return -EACCES;
+}
+
 __bpf_kfunc_start_defs();
 
 /* bpf_skb_get_hash - Get the flow hash of an skb.
-- 
2.20.1