[PATCH 4.9 104/130] packet: reset network header if packet shorter than ll reserved space

Greg Kroah-Hartman
2018-08-23T08:11:23Z

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

[ Upstream commit 993675a3100b16a4c80dfd70cbcde8ea7127b31d ]

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 <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/packet/af_packet.c | 2 ++
1 file changed, 2 insertions(+)

--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2917,6 +2917,8 @@ static int packet_snd(struct socket *soc
goto out_free;
} else if (reserve) {
skb_reserve(skb, -reserve);
+ if (len < reserve)
+ skb_reset_network_header(skb);
}

/* Returns -EFAULT on error */