samples/bpf: Fix broken tracex1 due to kprobe argument change

>From commit c0bbbdc32feb ("__netif_receive_skb_core: pass skb by
reference"), the first argument passed into __netif_receive_skb_core
has changed to reference of a skb pointer.

This commit fixes by using bpf_probe_read_kernel.

Signed-off-by: Yaqi Chen <chendotjs@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210416154803.37157-1-chendotjs@gmail.com

diff --git a/samples/bpf/tracex1_kern.c b/samples/bpf/tracex1_kern.c
index 3f4599c..ef30d2b 100644 (file)
--- a/samples/bpf/tracex1_kern.c
+++ b/samples/bpf/tracex1_kern.c
@@ -26,7 +26,7 @@
 SEC("kprobe/__netif_receive_skb_core")
 int bpf_prog1(struct pt_regs *ctx)
 {
-       /* attaches to kprobe netif_receive_skb,
+       /* attaches to kprobe __netif_receive_skb_core,
         * looks for packets on loobpack device and prints them
         */
        char devname[IFNAMSIZ];
@@ -35,7 +35,7 @@ int bpf_prog1(struct pt_regs *ctx)
        int len;
 
        /* non-portable! works for the given kernel only */
-       skb = (struct sk_buff *) PT_REGS_PARM1(ctx);
+       bpf_probe_read_kernel(&skb, sizeof(skb), (void *)PT_REGS_PARM1(ctx));
        dev = _(skb->dev);
        len = _(skb->len);