netdev - [Patch net] smc: disallow TCP_ULP in smc

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Message-Id: <20210410181732.25995-1-xiyou.wangcong@gmail.com>
Date:   Sat, 10 Apr 2021 11:17:32 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     linux-s390@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
        syzbot+b54a1ce86ba4a623b7f0@...kaller.appspotmail.com,
        John Fastabend <john.fastabend@...il.com>,
        Karsten Graul <kgraul@...ux.ibm.com>
Subject: [Patch net] smc: disallow TCP_ULP in smc_setsockopt()

From: Cong Wang <cong.wang@...edance.com>

syzbot is able to setup kTLS on an SMC socket, which coincidentally
uses sk_user_data too, later, kTLS treats it as psock so triggers a
refcnt warning. The cause is that smc_setsockopt() simply calls
TCP setsockopt(). I do not think it makes sense to setup kTLS on
top of SMC, so we can just disallow this.

Reported-and-tested-by: syzbot+b54a1ce86ba4a623b7f0@...kaller.appspotmail.com
Cc: John Fastabend <john.fastabend@...il.com>
Cc: Karsten Graul <kgraul@...ux.ibm.com>
Signed-off-by: Cong Wang <cong.wang@...edance.com>
---
 net/smc/af_smc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 47340b3b514f..0d4d6d28f20c 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -2162,6 +2162,9 @@ static int smc_setsockopt(struct socket *sock, int level, int optname,
 	struct smc_sock *smc;
 	int val, rc;
 
+	if (optname == TCP_ULP)
+		return -EOPNOTSUPP;
+
 	smc = smc_sk(sk);
 
 	/* generic setsockopts reaching us here always apply to the
@@ -2186,7 +2189,6 @@ static int smc_setsockopt(struct socket *sock, int level, int optname,
 	if (rc || smc->use_fallback)
 		goto out;
 	switch (optname) {
-	case TCP_ULP:
 	case TCP_FASTOPEN:
 	case TCP_FASTOPEN_CONNECT:
 	case TCP_FASTOPEN_KEY:
-- 
2.25.1