From ff46e3b4421923937b7f6e44ffcd3549a074f321 Mon Sep 17 00:00:00 2001 From: luoxuanqiang Date: Fri, 21 Jun 2024 09:39:29 +0800 Subject: Fix race for duplicate reqsk on identical SYN When bonding is configured in BOND_MODE_BROADCAST mode, if two identical SYN packets are received at the same time and processed on different CPUs, it can potentially create the same sk (sock) but two different reqsk (request_sock) in tcp_conn_request(). These two different reqsk will respond with two SYNACK packets, and since the generation of the seq (ISN) incorporates a timestamp, the final two SYNACK packets will have different seq values. The consequence is that when the Client receives and replies with an ACK to the earlier SYNACK packet, we will reset(RST) it. ======================================================================== This behavior is consistently reproducible in my local setup, which comprises: | NETA1 ------ NETB1 | PC_A --- bond --- | | --- bond --- PC_B | NETA2 ------ NETB2 | - PC_A is the Server and has two network cards, NETA1 and NETA2. I have bonded these two cards using BOND_MODE_BROADCAST mode and configured them to be handled by different CPU. - PC_B is the Client, also equipped with two network cards, NETB1 and NETB2, which are also bonded and configured in BOND_MODE_BROADCAST mode. If the client attempts a TCP connection to the server, it might encounter a failure. Capturing packets from the server side reveals: 10.10.10.10.45182 > localhost: Flags [S], seq 320236027, 10.10.10.10.45182 > localhost: Flags [S], seq 320236027, localhost > 10.10.10.10.45182: Flags [S.], seq 2967855116, localhost > 10.10.10.10.45182: Flags [S.], seq 2967855123, <== 10.10.10.10.45182 > localhost: Flags [.], ack 4294967290, 10.10.10.10.45182 > localhost: Flags [.], ack 4294967290, localhost > 10.10.10.10.45182: Flags [R], seq 2967855117, <== localhost > 10.10.10.10.45182: Flags [R], seq 2967855117, Two SYNACKs with different seq numbers are sent by localhost, resulting in an anomaly. ======================================================================== The attempted solution is as follows: Add a return value to inet_csk_reqsk_queue_hash_add() to confirm if the ehash insertion is successful (Up to now, the reason for unsuccessful insertion is that a reqsk for the same connection has already been inserted). If the insertion fails, release the reqsk. Due to the refcnt, Kuniyuki suggests also adding a return value check for the DCCP module; if ehash insertion fails, indicating a successful insertion of the same connection, simply release the reqsk as well. Simultaneously, In the reqsk_queue_hash_req(), the start of the req->rsk_timer is adjusted to be after successful insertion. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: luoxuanqiang Reviewed-by: Kuniyuki Iwashima Reviewed-by: Eric Dumazet Link: https://lore.kernel.org/r/20240621013929.1386815-1-luoxuanqiang@kylinos.cn Signed-off-by: Paolo Abeni --- net/dccp/ipv4.c | 7 +++++-- net/dccp/ipv6.c | 7 +++++-- 2 files changed, 10 insertions(+), 4 deletions(-) (limited to 'net/dccp') diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c index ff41bd6f99c3..5926159a6f20 100644 --- a/net/dccp/ipv4.c +++ b/net/dccp/ipv4.c @@ -657,8 +657,11 @@ int dccp_v4_conn_request(struct sock *sk, struct sk_buff *skb) if (dccp_v4_send_response(sk, req)) goto drop_and_free; - inet_csk_reqsk_queue_hash_add(sk, req, DCCP_TIMEOUT_INIT); - reqsk_put(req); + if (unlikely(!inet_csk_reqsk_queue_hash_add(sk, req, DCCP_TIMEOUT_INIT))) + reqsk_free(req); + else + reqsk_put(req); + return 0; drop_and_free: diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c index 85f4b8fdbe5e..da5dba120bc9 100644 --- a/net/dccp/ipv6.c +++ b/net/dccp/ipv6.c @@ -400,8 +400,11 @@ static int dccp_v6_conn_request(struct sock *sk, struct sk_buff *skb) if (dccp_v6_send_response(sk, req)) goto drop_and_free; - inet_csk_reqsk_queue_hash_add(sk, req, DCCP_TIMEOUT_INIT); - reqsk_put(req); + if (unlikely(!inet_csk_reqsk_queue_hash_add(sk, req, DCCP_TIMEOUT_INIT))) + reqsk_free(req); + else + reqsk_put(req); + return 0; drop_and_free: -- cgit v1.2.3