From: Ursula Braun <ubraun@linux.ibm.com>
Date: Fri, 14 Feb 2020 08:58:59 +0100
Subject: net/smc: transfer fasync_list in case of fallback
Git-commit: 67f562e3e147750a02b2a91d21a163fc44a1d13e
Patch-mainline: v5.6-rc2
References: git-fixes

SMC does not work together with FASTOPEN. If sendmsg() is called with
flag MSG_FASTOPEN in SMC_INIT state, the SMC-socket switches to
fallback mode. To handle the previous ioctl FIOASYNC call correctly
in this case, it is necessary to transfer the socket wait queue
fasync_list to the internal TCP socket.

Reported-by: syzbot+4b1fe8105f8044a26162@syzkaller.appspotmail.com
Fixes: ee9dfbef02d18 ("net/smc: handle sockopts forcing fallback")
Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Petr Tesarik <ptesarik@suse.com>

[ ptesarik: wq is a pointer in SLE15-SP1, because we do not
  have commit 333f7909a8573145811c4ab7d8c9092301707721. ]
---
 net/smc/af_smc.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -456,6 +456,8 @@ static void smc_switch_to_fallback(struc
 	if (smc->sk.sk_socket && smc->sk.sk_socket->file) {
 		smc->clcsock->file = smc->sk.sk_socket->file;
 		smc->clcsock->file->private_data = smc->clcsock;
+		smc->clcsock->wq->fasync_list =
+			smc->sk.sk_socket->wq->fasync_list;
 	}
 }