| From 8a8a0a058235860ad7a0be9a3e25ef032c7bf63b Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Fri, 9 Jul 2021 17:20:46 -0700 |
| Subject: mptcp: fix warning in __skb_flow_dissect() when do syn cookie for |
| subflow join |
| |
| From: Jianguo Wu <wujianguo@chinatelecom.cn> |
| |
| [ Upstream commit 0c71929b5893e410e0efbe1bbeca6f19a5f19956 ] |
| |
| I did stress test with wrk[1] and webfsd[2] with the assistance of |
| mptcp-tools[3]: |
| |
| Server side: |
| ./use_mptcp.sh webfsd -4 -R /tmp/ -p 8099 |
| Client side: |
| ./use_mptcp.sh wrk -c 200 -d 30 -t 4 http://192.168.174.129:8099/ |
| |
| and got the following warning message: |
| |
| [ 55.552626] TCP: request_sock_subflow: Possible SYN flooding on port 8099. Sending cookies. Check SNMP counters. |
| [ 55.553024] ------------[ cut here ]------------ |
| [ 55.553027] WARNING: CPU: 0 PID: 10 at net/core/flow_dissector.c:984 __skb_flow_dissect+0x280/0x1650 |
| ... |
| [ 55.553117] CPU: 0 PID: 10 Comm: ksoftirqd/0 Not tainted 5.12.0+ #18 |
| [ 55.553121] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 02/27/2020 |
| [ 55.553124] RIP: 0010:__skb_flow_dissect+0x280/0x1650 |
| ... |
| [ 55.553133] RSP: 0018:ffffb79580087770 EFLAGS: 00010246 |
| [ 55.553137] RAX: 0000000000000000 RBX: ffffffff8ddb58e0 RCX: ffffb79580087888 |
| [ 55.553139] RDX: ffffffff8ddb58e0 RSI: ffff8f7e4652b600 RDI: 0000000000000000 |
| [ 55.553141] RBP: ffffb79580087858 R08: 0000000000000000 R09: 0000000000000008 |
| [ 55.553143] R10: 000000008c622965 R11: 00000000d3313a5b R12: ffff8f7e4652b600 |
| [ 55.553146] R13: ffff8f7e465c9062 R14: 0000000000000000 R15: ffffb79580087888 |
| [ 55.553149] FS: 0000000000000000(0000) GS:ffff8f7f75e00000(0000) knlGS:0000000000000000 |
| [ 55.553152] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 |
| [ 55.553154] CR2: 00007f73d1d19000 CR3: 0000000135e10004 CR4: 00000000003706f0 |
| [ 55.553160] Call Trace: |
| [ 55.553166] ? __sha256_final+0x67/0xd0 |
| [ 55.553173] ? sha256+0x7e/0xa0 |
| [ 55.553177] __skb_get_hash+0x57/0x210 |
| [ 55.553182] subflow_init_req_cookie_join_save+0xac/0xc0 |
| [ 55.553189] subflow_check_req+0x474/0x550 |
| [ 55.553195] ? ip_route_output_key_hash+0x67/0x90 |
| [ 55.553200] ? xfrm_lookup_route+0x1d/0xa0 |
| [ 55.553207] subflow_v4_route_req+0x8e/0xd0 |
| [ 55.553212] tcp_conn_request+0x31e/0xab0 |
| [ 55.553218] ? selinux_socket_sock_rcv_skb+0x116/0x210 |
| [ 55.553224] ? tcp_rcv_state_process+0x179/0x6d0 |
| [ 55.553229] tcp_rcv_state_process+0x179/0x6d0 |
| [ 55.553235] tcp_v4_do_rcv+0xaf/0x220 |
| [ 55.553239] tcp_v4_rcv+0xce4/0xd80 |
| [ 55.553243] ? ip_route_input_rcu+0x246/0x260 |
| [ 55.553248] ip_protocol_deliver_rcu+0x35/0x1b0 |
| [ 55.553253] ip_local_deliver_finish+0x44/0x50 |
| [ 55.553258] ip_local_deliver+0x6c/0x110 |
| [ 55.553262] ? ip_rcv_finish_core.isra.19+0x5a/0x400 |
| [ 55.553267] ip_rcv+0xd1/0xe0 |
| ... |
| |
| After debugging, I found in __skb_flow_dissect(), skb->dev and skb->sk |
| are both NULL, then net is NULL, and trigger WARN_ON_ONCE(!net), |
| actually net is always NULL in this code path, as skb->dev is set to |
| NULL in tcp_v4_rcv(), and skb->sk is never set. |
| |
| Code snippet in __skb_flow_dissect() that trigger warning: |
| 975 if (skb) { |
| 976 if (!net) { |
| 977 if (skb->dev) |
| 978 net = dev_net(skb->dev); |
| 979 else if (skb->sk) |
| 980 net = sock_net(skb->sk); |
| 981 } |
| 982 } |
| 983 |
| 984 WARN_ON_ONCE(!net); |
| |
| So, using seq and transport header derived hash. |
| |
| [1] https://github.com/wg/wrk |
| [2] https://github.com/ourway/webfsd |
| [3] https://github.com/pabeni/mptcp-tools |
| |
| Fixes: 9466a1ccebbe ("mptcp: enable JOIN requests even if cookies are in use") |
| Suggested-by: Paolo Abeni <pabeni@redhat.com> |
| Suggested-by: Florian Westphal <fw@strlen.de> |
| Signed-off-by: Jianguo Wu <wujianguo@chinatelecom.cn> |
| Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com> |
| Signed-off-by: David S. Miller <davem@davemloft.net> |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| net/mptcp/syncookies.c | 16 +++++++++++++++- |
| 1 file changed, 15 insertions(+), 1 deletion(-) |
| |
| diff --git a/net/mptcp/syncookies.c b/net/mptcp/syncookies.c |
| index abe0fd099746..37127781aee9 100644 |
| --- a/net/mptcp/syncookies.c |
| +++ b/net/mptcp/syncookies.c |
| @@ -37,7 +37,21 @@ static spinlock_t join_entry_locks[COOKIE_JOIN_SLOTS] __cacheline_aligned_in_smp |
| |
| static u32 mptcp_join_entry_hash(struct sk_buff *skb, struct net *net) |
| { |
| - u32 i = skb_get_hash(skb) ^ net_hash_mix(net); |
| + static u32 mptcp_join_hash_secret __read_mostly; |
| + struct tcphdr *th = tcp_hdr(skb); |
| + u32 seq, i; |
| + |
| + net_get_random_once(&mptcp_join_hash_secret, |
| + sizeof(mptcp_join_hash_secret)); |
| + |
| + if (th->syn) |
| + seq = TCP_SKB_CB(skb)->seq; |
| + else |
| + seq = TCP_SKB_CB(skb)->seq - 1; |
| + |
| + i = jhash_3words(seq, net_hash_mix(net), |
| + (__force __u32)th->source << 16 | (__force __u32)th->dest, |
| + mptcp_join_hash_secret); |
| |
| return i % ARRAY_SIZE(join_entries); |
| } |
| -- |
| 2.30.2 |
| |