From: Peilin Ye peilin.ye@bytedance.com
[ Upstream commit ab198e1d0dd8dc4bc7575fb50758e2cbd51e14e1 ]
Feng reported an skb_under_panic BUG triggered by running test_ip6gretap() in tools/testing/selftests/bpf/test_tunnel.sh:
[ 82.492551] skbuff: skb_under_panic: text:ffffffffb268bb8e len:403 put:12 head:ffff9997c5480000 data:ffff9997c547fff8 tail:0x18b end:0x2c0 dev:ip6gretap11 <...> [ 82.607380] Call Trace: [ 82.609389] <TASK> [ 82.611136] skb_push.cold.109+0x10/0x10 [ 82.614289] __gre6_xmit+0x41e/0x590 [ 82.617169] ip6gre_tunnel_xmit+0x344/0x3f0 [ 82.620526] dev_hard_start_xmit+0xf1/0x330 [ 82.623882] sch_direct_xmit+0xe4/0x250 [ 82.626961] __dev_queue_xmit+0x720/0xfe0 <...> [ 82.633431] packet_sendmsg+0x96a/0x1cb0 [ 82.636568] sock_sendmsg+0x30/0x40 <...>
The following sequence of events caused the BUG:
1. During ip6gretap device initialization, tunnel->tun_hlen (e.g. 4) is calculated based on old flags (see ip6gre_calc_hlen()); 2. packet_snd() reserves header room for skb A, assuming tunnel->tun_hlen is 4; 3. Later (in clsact Qdisc), the eBPF program sets a new tunnel key for skb A using bpf_skb_set_tunnel_key() (see _ip6gretap_set_tunnel()); 4. __gre6_xmit() detects the new tunnel key, and recalculates "tun_hlen" (e.g. 12) based on new flags (e.g. TUNNEL_KEY and TUNNEL_SEQ); 5. gre_build_header() calls skb_push() with insufficient reserved header room, triggering the BUG.
As sugguested by Cong, fix it by moving the call to skb_cow_head() after the recalculation of tun_hlen.
Reproducer:
OBJ=$LINUX/tools/testing/selftests/bpf/test_tunnel_kern.o
ip netns add at_ns0 ip link add veth0 type veth peer name veth1 ip link set veth0 netns at_ns0 ip netns exec at_ns0 ip addr add 172.16.1.100/24 dev veth0 ip netns exec at_ns0 ip link set dev veth0 up ip link set dev veth1 up mtu 1500 ip addr add dev veth1 172.16.1.200/24
ip netns exec at_ns0 ip addr add ::11/96 dev veth0 ip netns exec at_ns0 ip link set dev veth0 up ip addr add dev veth1 ::22/96 ip link set dev veth1 up
ip netns exec at_ns0 \ ip link add dev ip6gretap00 type ip6gretap seq flowlabel 0xbcdef key 2 \ local ::11 remote ::22
ip netns exec at_ns0 ip addr add dev ip6gretap00 10.1.1.100/24 ip netns exec at_ns0 ip addr add dev ip6gretap00 fc80::100/96 ip netns exec at_ns0 ip link set dev ip6gretap00 up
ip link add dev ip6gretap11 type ip6gretap external ip addr add dev ip6gretap11 10.1.1.200/24 ip addr add dev ip6gretap11 fc80::200/24 ip link set dev ip6gretap11 up
tc qdisc add dev ip6gretap11 clsact tc filter add dev ip6gretap11 egress bpf da obj $OBJ sec ip6gretap_set_tunnel tc filter add dev ip6gretap11 ingress bpf da obj $OBJ sec ip6gretap_get_tunnel
ping6 -c 3 -w 10 -q ::11
Fixes: 6712abc168eb ("ip6_gre: add ip6 gre and gretap collect_md mode") Reported-by: Feng Zhou zhoufeng.zf@bytedance.com Co-developed-by: Cong Wang cong.wang@bytedance.com Signed-off-by: Cong Wang cong.wang@bytedance.com Signed-off-by: Peilin Ye peilin.ye@bytedance.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv6/ip6_gre.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c index b43a46449130..976236736146 100644 --- a/net/ipv6/ip6_gre.c +++ b/net/ipv6/ip6_gre.c @@ -733,9 +733,6 @@ static netdev_tx_t __gre6_xmit(struct sk_buff *skb, else fl6->daddr = tunnel->parms.raddr;
- if (skb_cow_head(skb, dev->needed_headroom ?: tunnel->hlen)) - return -ENOMEM; - /* Push GRE header. */ protocol = (dev->type == ARPHRD_ETHER) ? htons(ETH_P_TEB) : proto;
@@ -763,6 +760,9 @@ static netdev_tx_t __gre6_xmit(struct sk_buff *skb, (TUNNEL_CSUM | TUNNEL_KEY | TUNNEL_SEQ); tun_hlen = gre_calc_hlen(flags);
+ if (skb_cow_head(skb, dev->needed_headroom ?: tun_hlen + tunnel->encap_hlen)) + return -ENOMEM; + gre_build_header(skb, tun_hlen, flags, protocol, tunnel_id_to_key32(tun_info->key.tun_id), @@ -773,6 +773,9 @@ static netdev_tx_t __gre6_xmit(struct sk_buff *skb, if (tunnel->parms.o_flags & TUNNEL_SEQ) tunnel->o_seqno++;
+ if (skb_cow_head(skb, dev->needed_headroom ?: tunnel->hlen)) + return -ENOMEM; + gre_build_header(skb, tunnel->tun_hlen, tunnel->parms.o_flags, protocol, tunnel->parms.o_key, htonl(tunnel->o_seqno));