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Date: Fri, 14 Jun 2024 08:47:07 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: luoxuanqiang <luoxuanqiang@...inos.cn>, Florian Westphal <fw@...len.de>
Cc: davem@...emloft.net, dsahern@...nel.org, kuba@...nel.org,
pabeni@...hat.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/1] Fix race for duplicate reqsk on identical SYN
On Fri, Jun 14, 2024 at 8:01 AM luoxuanqiang <luoxuanqiang@...inos.cn> wrote:
>
> 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.localdomain.search-agent: Flags [S], seq 320236027,
> 10.10.10.10.45182 > localhost.localdomain.search-agent: Flags [S], seq 320236027,
> localhost.localdomain.search-agent > 10.10.10.10.45182: Flags [S.], seq 2967855116,
> localhost.localdomain.search-agent > 10.10.10.10.45182: Flags [S.], seq 2967855123, <==
> 10.10.10.10.45182 > localhost.localdomain.search-agent: Flags [.], ack 4294967290,
> 10.10.10.10.45182 > localhost.localdomain.search-agent: Flags [.], ack 4294967290,
> localhost.localdomain.search-agent > 10.10.10.10.45182: Flags [R], seq 2967855117, <==
> localhost.localdomain.search-agent > 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:
> In the tcp_conn_request(), while inserting reqsk into the ehash table, it also checks
> if an entry already exists. If found, it avoids reinsertion and releases it.
>
> Simultaneously, In the reqsk_queue_hash_req(), the start of the req->rsk_timer is
> adjusted to be after successful insertion.
>
> Signed-off-by: luoxuanqiang <luoxuanqiang@...inos.cn>
> ---
> include/net/inet_connection_sock.h | 2 +-
> net/dccp/ipv4.c | 2 +-
> net/dccp/ipv6.c | 2 +-
> net/ipv4/inet_connection_sock.c | 16 ++++++++++++----
> net/ipv4/tcp_input.c | 11 ++++++++++-
> 5 files changed, 25 insertions(+), 8 deletions(-)
>
> diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
> index 7d6b1254c92d..8773d161d184 100644
> --- a/include/net/inet_connection_sock.h
> +++ b/include/net/inet_connection_sock.h
> @@ -264,7 +264,7 @@ struct sock *inet_csk_reqsk_queue_add(struct sock *sk,
> struct request_sock *req,
> struct sock *child);
> void inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req,
> - unsigned long timeout);
> + unsigned long timeout, bool *found_dup_sk);
> struct sock *inet_csk_complete_hashdance(struct sock *sk, struct sock *child,
> struct request_sock *req,
> bool own_req);
> diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
> index ff41bd6f99c3..13aafdeb9205 100644
> --- a/net/dccp/ipv4.c
> +++ b/net/dccp/ipv4.c
> @@ -657,7 +657,7 @@ 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);
> + inet_csk_reqsk_queue_hash_add(sk, req, DCCP_TIMEOUT_INIT, NULL);
> reqsk_put(req);
> return 0;
>
> diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
> index 85f4b8fdbe5e..493cdb12ce2b 100644
> --- a/net/dccp/ipv6.c
> +++ b/net/dccp/ipv6.c
> @@ -400,7 +400,7 @@ 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);
> + inet_csk_reqsk_queue_hash_add(sk, req, DCCP_TIMEOUT_INIT, NULL);
> reqsk_put(req);
> return 0;
>
> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> index d81f74ce0f02..d9394db98a5a 100644
> --- a/net/ipv4/inet_connection_sock.c
> +++ b/net/ipv4/inet_connection_sock.c
> @@ -1123,12 +1123,17 @@ static void reqsk_timer_handler(struct timer_list *t)
> }
>
> static void reqsk_queue_hash_req(struct request_sock *req,
> - unsigned long timeout)
> + unsigned long timeout, bool *found_dup_sk)
> {
> +
> + inet_ehash_insert(req_to_sk(req), NULL, found_dup_sk);
> + if(found_dup_sk && *found_dup_sk)
> + return;
> +
> + /* The timer needs to be setup after a successful insertion. */
I am pretty sure we had a prior attempt to fix this issue, and the fix
was problematic.
You are moving the inet_ehash_insert() before the mod_timer(), this
will add races.
Hint here is the use of TIMER_PINNED.
CCing Florian, because he just removed TIMER_PINNED for TW, he might
have the context
to properly fix this issue.
> timer_setup(&req->rsk_timer, reqsk_timer_handler, TIMER_PINNED);
> mod_timer(&req->rsk_timer, jiffies + timeout);
>
> - inet_ehash_insert(req_to_sk(req), NULL, NULL);
> /* before letting lookups find us, make sure all req fields
> * are committed to memory and refcnt initialized.
> */
> @@ -1137,9 +1142,12 @@ static void reqsk_queue_hash_req(struct request_sock *req,
> }
>
> void inet_csk_reqsk_queue_hash_add(struct sock *sk, struct request_sock *req,
> - unsigned long timeout)
> + unsigned long timeout, bool *found_dup_sk)
> {
> - reqsk_queue_hash_req(req, timeout);
> + reqsk_queue_hash_req(req, timeout, found_dup_sk);
> + if(found_dup_sk && *found_dup_sk)
> + return;
> +
> inet_csk_reqsk_queue_added(sk);
> }
> EXPORT_SYMBOL_GPL(inet_csk_reqsk_queue_hash_add);
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 9c04a9c8be9d..467f1b7bbd5a 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -7255,8 +7255,17 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
> } else {
> tcp_rsk(req)->tfo_listener = false;
> if (!want_cookie) {
> + bool found_dup_sk = false;
> +
> req->timeout = tcp_timeout_init((struct sock *)req);
> - inet_csk_reqsk_queue_hash_add(sk, req, req->timeout);
> + inet_csk_reqsk_queue_hash_add(sk, req, req->timeout,
> + &found_dup_sk);
> +
> + if(unlikely(found_dup_sk)){
> + reqsk_free(req);
> + return 0;
> + }
> +
> }
> af_ops->send_synack(sk, dst, &fl, req, &foc,
> !want_cookie ? TCP_SYNACK_NORMAL :
> --
> 2.25.1
>
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