bpf: remove redundant null pointer check before consume_skb

mainline inclusion
from mainline-v4.20-rc1
commit 788758d1
category: other
bugzilla: 43460
CVE: NA

---------------------------------------
consume_skb has taken the null pointer into account. hence it is safe
to remove the redundant null pointer check before consume_skb.
Signed-off-by: Nzhong jiang <zhongjiang@huawei.com>
Acked-by: NSong Liu <songliubraving@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Nliuxin <liuxin264@huawei.com>
Reviewed-by: NCheng Jian <cj.chengjian@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

kernel/bpf/sockmap.c

@@ -612,8 +612,7 @@ static int free_sg(struct sock *sk, int start,
 		if (i == MAX_SKB_FRAGS)
 			i = 0;
 	}
-	if (md->skb)
-		consume_skb(md->skb);
+	consume_skb(md->skb);
 
 	return free;
 }
@@ -995,8 +994,7 @@ static int bpf_tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 
 		if (!sg->length && md->sg_start == md->sg_end) {
 			list_del(&md->list);
-			if (md->skb)
-				consume_skb(md->skb);
+			consume_skb(md->skb);
 			kfree(md);
 		}
 	}