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

stable inclusion
from stable-5.10.38
commit 799c3950680a748355bc62f835ab5608b99c2288
bugzilla: 51875
CVE: NA

--------------------------------

[ Upstream commit 137733d0 ]

>From commit c0bbbdc3 ("__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: NYaqi Chen <chendotjs@gmail.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210416154803.37157-1-chendotjs@gmail.comSigned-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

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);