From 832ba596494b2c9eac7760259eff2d8b7dcad0ee Mon Sep 17 00:00:00 2001
From: Antoine Tenart <atenart@kernel.org>
Date: Mon, 30 Nov 2020 17:19:11 +0100
Subject: [PATCH] net: ip6_gre: set dev->hard_header_len when using header_ops
syzkaller managed to crash the kernel using an NBMA ip6gre interface. I
could reproduce it creating an NBMA ip6gre interface and forwarding
traffic to it:
skbuff: skb_under_panic: text:ffffffff8250e927 len:148 put:44 head:ffff8c03c7a33
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:109!
Call Trace:
skb_push+0x10/0x10
ip6gre_header+0x47/0x1b0
neigh_connected_output+0xae/0xf0
ip6gre tunnel provides its own header_ops->create, and sets it
conditionally when initializing the tunnel in NBMA mode. When
header_ops->create is used, dev->hard_header_len should reflect the
length of the header created. Otherwise, when not used,
dev->needed_headroom should be used.
Fixes: eb95f52fc72d ("net: ipv6_gre: Fix GRO to work on IPv6 over GRE tap")
Cc: Maria Pasechnik <mariap@mellanox.com>
Signed-off-by: Antoine Tenart <atenart@kernel.org>
Link: https://lore.kernel.org/r/20201130161911.464106-1-atenart@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
net/ipv6/ip6_gre.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 931b186d2e4869..cf6e1380b527c3 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -1133,8 +1133,13 @@ static void ip6gre_tnl_link_config_route(struct ip6_tnl *t, int set_mtu,
return;
if (rt->dst.dev) {
- dev->needed_headroom = rt->dst.dev->hard_header_len +
- t_hlen;
+ unsigned short dst_len = rt->dst.dev->hard_header_len +
+ t_hlen;
+
+ if (t->dev->header_ops)
+ dev->hard_header_len = dst_len;
+ else
+ dev->needed_headroom = dst_len;
if (set_mtu) {
dev->mtu = rt->dst.dev->mtu - t_hlen;
@@ -1159,7 +1164,12 @@ static int ip6gre_calc_hlen(struct ip6_tnl *tunnel)
tunnel->hlen = tunnel->tun_hlen + tunnel->encap_hlen;
t_hlen = tunnel->hlen + sizeof(struct ipv6hdr);
- tunnel->dev->needed_headroom = LL_MAX_HEADER + t_hlen;
+
+ if (tunnel->dev->header_ops)
+ tunnel->dev->hard_header_len = LL_MAX_HEADER + t_hlen;
+ else
+ tunnel->dev->needed_headroom = LL_MAX_HEADER + t_hlen;
+
return t_hlen;
}
--
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