[PATCH 5.8 558/633] ip_gre: set dev->hard_header_len and dev->needed_headroom properly

Greg Kroah-Hartman
2020-10-27T16:51:40Z

From: Cong Wang <xiyou.wangcong@gmail.com>

[ Upstream commit fdafed459998e2be0e877e6189b24cb7a0183224 ]

GRE tunnel has its own header_ops, ipgre_header_ops, and sets it
conditionally. When it is set, it assumes the outer IP header is
already created before ipgre_xmit().

This is not true when we send packets through a raw packet socket,
where L2 headers are supposed to be constructed by user. Packet
socket calls dev_validate_header() to validate the header. But
GRE tunnel does not set dev->hard_header_len, so that check can
be simply bypassed, therefore uninit memory could be passed down
to ipgre_xmit(). Similar for dev->needed_headroom.

dev->hard_header_len is supposed to be the length of the header
created by dev->header_ops->create(), so it should be used whenever
header_ops is set, and dev->needed_headroom should be used when it
is not set.

Reported-and-tested-by: syzbot+4a2c52677a8a1aa283cb@syzkaller.appspotmail.com
Cc: William Tu <u9012063@gmail.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Xie He <xie.he.0141@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv4/ip_gre.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 4e31f23e4117e..e70291748889b 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -625,9 +625,7 @@ static netdev_tx_t ipgre_xmit(struct sk_buff *skb,
}

if (dev->header_ops) {
- /* Need space for new headers */
- if (skb_cow_head(skb, dev->needed_headroom -
- (tunnel->hlen + sizeof(struct iphdr))))
+ if (skb_cow_head(skb, 0))
goto free_skb;

tnl_params = (const struct iphdr *)skb->data;
@@ -748,7 +746,11 @@ static void ipgre_link_update(struct net_device *dev, bool set_mtu)
len = tunnel->tun_hlen - len;
tunnel->hlen = tunnel->hlen + len;

- dev->needed_headroom = dev->needed_headroom + len;
+ if (dev->header_ops)
+ dev->hard_header_len += len;
+ else
+ dev->needed_headroom += len;
+
if (set_mtu)
dev->mtu = max_t(int, dev->mtu - len, 68);

@@ -944,6 +946,7 @@ static void __gre_tunnel_init(struct net_device *dev)
tunnel->parms.iph.protocol = IPPROTO_GRE;

tunnel->hlen = tunnel->tun_hlen + tunnel->encap_hlen;
+ dev->needed_headroom = tunnel->hlen + sizeof(tunnel->parms.iph);

dev->features |= GRE_FEATURES;
dev->hw_features |= GRE_FEATURES;
@@ -987,10 +990,14 @@ static int ipgre_tunnel_init(struct net_device *dev)
return -EINVAL;
dev->flags = IFF_BROADCAST;
dev->header_ops = &ipgre_header_ops;
+ dev->hard_header_len = tunnel->hlen + sizeof(*iph);
+ dev->needed_headroom = 0;
}
#endif
} else if (!tunnel->collect_md) {
dev->header_ops = &ipgre_header_ops;
+ dev->hard_header_len = tunnel->hlen + sizeof(*iph);
+ dev->needed_headroom = 0;
}

return ip_tunnel_init(dev);
--
2.25.1