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+4a2c52677a8a1aa28...@syzkaller.appspotmail.com
Cc: Xie He <xie.he.0...@gmail.com>
Cc: William Tu <u9012...@gmail.com>
Cc: Willem de Bruijn <willemdebruijn.ker...@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
---
Note, there are some other suspicious use of dev->hard_header_len in
the same file, but let's leave them to a separate patch if really
needed.
net/ipv4/ip_gre.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 4e31f23e4117..82fee0010353 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -626,8 +626,7 @@ 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, dev->hard_header_len))
goto free_skb;
tnl_params = (const struct iphdr *)skb->data;
@@ -748,7 +747,11 @@ 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 +947,7 @@ 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 +991,14 @@ 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);
--
2.28.0
