[PATCH net-next 3/3] bpf: add helper to invalidate hash

[Daniel Borkmann]

Add a small helper that complements 36bbef52c7eb ("bpf: direct packet
write and access for helpers for clsact progs") for invalidating the
current skb->hash after mangling on headers via direct packet write.

Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
Acked-by: Alexei Starovoitov <a...@kernel.org>
---
 include/uapi/linux/bpf.h |  7 +++++++
 net/core/filter.c        | 18 ++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index e07432b..f09c70b 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -419,6 +419,13 @@ enum bpf_func_id {
         */
        BPF_FUNC_csum_update,
 
+       /**
+        * bpf_set_hash_invalid(skb)
+        * Invalidate current skb>hash.
+        * @skb: pointer to skb
+        */
+       BPF_FUNC_set_hash_invalid,
+
        __BPF_FUNC_MAX_ID,
 };
 
diff --git a/net/core/filter.c b/net/core/filter.c
index acf84fb..00351cd 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1777,6 +1777,22 @@ static const struct bpf_func_proto 
bpf_get_hash_recalc_proto = {
        .arg1_type      = ARG_PTR_TO_CTX,
 };
 
+BPF_CALL_1(bpf_set_hash_invalid, struct sk_buff *, skb)
+{
+       /* After all direct packet write, this can be used once for
+        * triggering a lazy recalc on next skb_get_hash() invocation.
+        */
+       skb_clear_hash(skb);
+       return 0;
+}
+
+static const struct bpf_func_proto bpf_set_hash_invalid_proto = {
+       .func           = bpf_set_hash_invalid,
+       .gpl_only       = false,
+       .ret_type       = RET_INTEGER,
+       .arg1_type      = ARG_PTR_TO_CTX,
+};
+
 BPF_CALL_3(bpf_skb_vlan_push, struct sk_buff *, skb, __be16, vlan_proto,
           u16, vlan_tci)
 {
@@ -2534,6 +2550,8 @@ tc_cls_act_func_proto(enum bpf_func_id func_id)
                return &bpf_get_route_realm_proto;
        case BPF_FUNC_get_hash_recalc:
                return &bpf_get_hash_recalc_proto;
+       case BPF_FUNC_set_hash_invalid:
+               return &bpf_set_hash_invalid_proto;
        case BPF_FUNC_perf_event_output:
                return &bpf_skb_event_output_proto;
        case BPF_FUNC_get_smp_processor_id:
-- 
1.9.3