[PATCH v2] tcp: relookup sock for RST+ACK packets handled by obsolete req sock

Currently tcp_check_req can be called with obsolete req socket for which big
socket have been already created (because of CPU race or early demux
assigning req socket to multiple packets in gro batch).

Commit e0f9759f530bf789e984 ("tcp: try to keep packet if SYN_RCV race
is lost") added retry in case when tcp_check_req is called for PSH|ACK packet.
But if client sends RST+ACK immediatly after connection being
established (it is performing healthcheck, for example) retry does not
occur. In that case tcp_check_req tries to close req socket,
leaving big socket active.

Fixes: e0f9759f530 ("tcp: try to keep packet if SYN_RCV race is lost")
Signed-off-by: Alexander Ovechkin <redacted>
Reported-by: Oleg Senin <redacted>
---
 include/net/inet_connection_sock.h | 2 +-
 net/ipv4/inet_connection_sock.c    | 7 +++++--
 net/ipv4/tcp_minisocks.c           | 7 +++++--
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index 10a625760de9..3c8c59471bc1 100644
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h

@@ -282,7 +282,7 @@ static inline int inet_csk_reqsk_queue_is_full(const struct sock *sk)
 	return inet_csk_reqsk_queue_len(sk) >= sk->sk_max_ack_backlog;
 }
 
-void inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req);
+bool inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req);
 void inet_csk_reqsk_queue_drop_and_put(struct sock *sk, struct request_sock *req);
 
 static inline void inet_csk_prepare_for_destroy_sock(struct sock *sk)

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 6bd7ca09af03..fd472eae4f5c 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c

@@ -705,12 +705,15 @@ static bool reqsk_queue_unlink(struct request_sock *req)
 	return found;
 }
 
-void inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req)
+bool inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req)
 {
-	if (reqsk_queue_unlink(req)) {
+	bool unlinked = reqsk_queue_unlink(req);
+
+	if (unlinked) {
 		reqsk_queue_removed(&inet_csk(sk)->icsk_accept_queue, req);
 		reqsk_put(req);
 	}
+	return unlinked;
 }
 EXPORT_SYMBOL(inet_csk_reqsk_queue_drop);
 

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 0055ae0a3bf8..7513ba45553d 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c

@@ -804,8 +804,11 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 		tcp_reset(sk, skb);
 	}
 	if (!fastopen) {
-		inet_csk_reqsk_queue_drop(sk, req);
-		__NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
+		bool unlinked = inet_csk_reqsk_queue_drop(sk, req);
+
+		if (unlinked)
+			__NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS);
+		*req_stolen = !unlinked;
 	}
 	return NULL;
 }

-- 
2.17.1

On Mon, Mar 15, 2021 at 12:06 PM Alexander Ovechkin [off-list ref] wrote:

Currently tcp_check_req can be called with obsolete req socket for which big
socket have been already created (because of CPU race or early demux
assigning req socket to multiple packets in gro batch).

Commit e0f9759f530bf789e984 ("tcp: try to keep packet if SYN_RCV race
is lost") added retry in case when tcp_check_req is called for PSH|ACK packet.
But if client sends RST+ACK immediatly after connection being
established (it is performing healthcheck, for example) retry does not
occur. In that case tcp_check_req tries to close req socket,
leaving big socket active.

Fixes: e0f9759f530 ("tcp: try to keep packet if SYN_RCV race is lost")
Signed-off-by: Alexander Ovechkin <redacted>
Reported-by: Oleg Senin <redacted>
---

SGTM, thanks.

Reviewed-by: Eric Dumazet <edumazet@google.com>

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Mon, 15 Mar 2021 14:05:45 +0300 you wrote:

Currently tcp_check_req can be called with obsolete req socket for which big
socket have been already created (because of CPU race or early demux
assigning req socket to multiple packets in gro batch).

Commit e0f9759f530bf789e984 ("tcp: try to keep packet if SYN_RCV race
is lost") added retry in case when tcp_check_req is called for PSH|ACK packet.
But if client sends RST+ACK immediatly after connection being
established (it is performing healthcheck, for example) retry does not
occur. In that case tcp_check_req tries to close req socket,
leaving big socket active.

[...]

Here is the summary with links:
  - [v2] tcp: relookup sock for RST+ACK packets handled by obsolete req sock
    https://git.kernel.org/netdev/net/c/7233da86697e

You are awesome, thank you!
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