[PATCH net] packet: reset network header if packet shorter than ll reserved space

[Willem de Bruijn]

From: Willem de Bruijn <will...@google.com>

If variable length link layer headers result in a packet shorter
than dev->hard_header_len, reset the network header offset. Else
skb->mac_len may exceed skb->len after skb_mac_reset_len.

packet_sendmsg_spkt already has similar logic.

Fixes: b84bbaf7a6c8 ("packet: in packet_snd start writing at link layer 
allocation")
Signed-off-by: Willem de Bruijn <will...@google.com>
---
 net/packet/af_packet.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 57634bc3da74..9b27d0cd766d 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2878,6 +2878,8 @@ static int packet_snd(struct socket *sock, struct msghdr 
*msg, size_t len)
                        goto out_free;
        } else if (reserve) {
                skb_reserve(skb, -reserve);
+               if (len < reserve)
+                       skb_reset_network_header(skb);
        }
 
        /* Returns -EFAULT on error */
-- 
2.18.0.203.gfac676dfb9-goog