[PATCH net] bpf: test_run: fix WARNING in format_decode

[Edward Adam Davis]

Confirm that skb->len is not 0 to ensure that skb length is valid.

Fixes: 114039b34201 ("bpf: Move skb->len == 0 checks into __bpf_redirect")
Reported-by: syzbot+e2c932aec5c8a6e1d...@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eada...@qq.com>
---
 net/bpf/test_run.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index c9fdcc5cdce1..78258a822a5c 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -845,6 +845,9 @@ static int convert___skb_to_skb(struct sk_buff *skb, struct 
__sk_buff *__skb)
 {
        struct qdisc_skb_cb *cb = (struct qdisc_skb_cb *)skb->cb;
 
+       if (!skb->len)
+               return -EINVAL;
+
        if (!__skb)
                return 0;
 
-- 
2.26.1