Commit b84bbaf7 authored May 11, 2018 by Willem de Bruijn Committed by David S. Miller May 13, 2018

packet: in packet_snd start writing at link layer allocation



Packet sockets allow construction of packets shorter than
dev->hard_header_len to accommodate protocols with variable length
link layer headers. These packets are padded to dev->hard_header_len,
because some device drivers interpret that as a minimum packet size.

packet_snd reserves dev->hard_header_len bytes on allocation.
SOCK_DGRAM sockets call skb_push in dev_hard_header() to ensure that
link layer headers are stored in the reserved range. SOCK_RAW sockets
do the same in tpacket_snd, but not in packet_snd.

Syzbot was able to send a zero byte packet to a device with massive
116B link layer header, causing padding to cross over into skb_shinfo.
Fix this by writing from the start of the llheader reserved range also
in the case of packet_snd/SOCK_RAW.

Update skb_set_network_header to the new offset. This also corrects
it for SOCK_DGRAM, where it incorrectly double counted reserve due to
the skb_push in dev_hard_header.

Fixes: 9ed988cd ("packet: validate variable length ll headers")
Reported-by:  <syzbot+71d74a5406d02057d559@syzkaller.appspotmail.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 4bc87198

net/packet/af_packet.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -2903,13 +2903,15 @@ static int packet_snd(struct socket sock, struct msghdr msg, size_t len)
		if (skb == NULL)
		goto out_unlock;

		skb_set_network_header(skb, reserve);
		skb_reset_network_header(skb);

		err = -EINVAL;
		if (sock->type == SOCK_DGRAM) {
		offset = dev_hard_header(skb, dev, ntohs(proto), addr, NULL, len);
		if (unlikely(offset < 0))
		goto out_free;
		} else if (reserve) {
		skb_push(skb, reserve);
		}

		/* Returns -EFAULT on error */

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