From: "Nikita V. Shirokov" <tehnerd@tehnerd.com>
Date: Wed, 25 Apr 2018 07:15:03 -0700
Subject: bpf: fix xdp_generic for bpf_adjust_tail usecase
Patch-mainline: v4.18-rc1
Git-commit: f761312023a1f0d625e34daadd54c3f9cb2a4ac2
References: bsc#1109837

When bpf_adjust_tail was introduced for generic xdp, it changed skb's tail
pointer, so it was pointing to the new "end of the packet". However skb's
len field wasn't properly modified, so on the wire ethernet frame had
original (or even bigger, if adjust_head was used) size. This diff is
fixing this.

Fixes: 198d83bb3 (" bpf: make generic xdp compatible w/ bpf_xdp_adjust_tail")
Signed-off-by: Nikita V. Shirokov <tehnerd@tehnerd.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 net/core/dev.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4014,8 +4014,10 @@ static u32 netif_receive_generic_xdp(str
 	 * pckt.
 	 */
 	off = orig_data_end - xdp.data_end;
-	if (off != 0)
+	if (off != 0) {
 		skb_set_tail_pointer(skb, xdp.data_end - xdp.data);
+		skb->len -= off;
+	}
 
 	switch (act) {
 	case XDP_REDIRECT: