From 832ba596494b2c9eac7760259eff2d8b7dcad0ee Mon Sep 17 00:00:00 2001 From: Antoine Tenart 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 Signed-off-by: Antoine Tenart Link: https://lore.kernel.org/r/20201130161911.464106-1-atenart@kernel.org Signed-off-by: Jakub Kicinski --- 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 931b186..cf6e138 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; } -- 2.7.4