sched, bpf: make skb->priority writable

{cls,act}_bpf can now set the skb->priority from an eBPF program based
on various critera, so that for example classful qdiscs like multiq can
update the skb's priority during enqueue time and further push it down
into subsequent qdiscs.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/filter.c b/net/core/filter.c
index 45c69ce4c847f2d23bcb2be873b5748255c5e1b1..53a5036fb32d26f3c6c42decd6112b53206b4187 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1721,6 +1721,7 @@ static bool tc_cls_act_is_valid_access(int off, int size,
                switch (off) {
                case offsetof(struct __sk_buff, mark):
                case offsetof(struct __sk_buff, tc_index):
+               case offsetof(struct __sk_buff, priority):
                case offsetof(struct __sk_buff, cb[0]) ...
                        offsetof(struct __sk_buff, cb[4]):
                        break;
@@ -1762,8 +1763,12 @@ static u32 bpf_net_convert_ctx_access(enum bpf_access_type type, int dst_reg,
        case offsetof(struct __sk_buff, priority):
                BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, priority) != 4);
 
-               *insn++ = BPF_LDX_MEM(BPF_W, dst_reg, src_reg,
-                                     offsetof(struct sk_buff, priority));
+               if (type == BPF_WRITE)
+                       *insn++ = BPF_STX_MEM(BPF_W, dst_reg, src_reg,
+                                             offsetof(struct sk_buff, priority));
+               else
+                       *insn++ = BPF_LDX_MEM(BPF_W, dst_reg, src_reg,
+                                             offsetof(struct sk_buff, priority));
                break;
 
        case offsetof(struct __sk_buff, ingress_ifindex):