path: root/net/packet
diff options
authorWillem de Bruijn <willemb@google.com>2018-05-11 13:24:25 -0400
committerDavid S. Miller <davem@davemloft.net>2018-05-13 20:19:27 -0400
commitb84bbaf7a6c8cca24f8acf25a2c8e46913a947ba (patch)
treebef9a144ff2af69bb75960f9c048d83b491201c1 /net/packet
parent4bc871984f7cb5b2dec3ae64b570cb02f9ce2227 (diff)
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: 9ed988cd5915 ("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>
Diffstat (limited to 'net/packet')
1 files changed, 3 insertions, 1 deletions
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 01f3515cada0..e9422fe45179 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -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 */