netdev - [Patch net] smc: move unhash as early as possible in smc

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Message-Id: <20190106074526.4882-1-xiyou.wangcong@gmail.com>
Date:   Sat,  5 Jan 2019 23:45:26 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        syzbot+fbd1e5476e4c94c7b34e@...kaller.appspotmail.com,
        Ursula Braun <ubraun@...ux.ibm.com>
Subject: [Patch net] smc: move unhash as early as possible in smc_release()

In smc_release() we release smc->clcsock before unhash the smc
sock, but a parallel smc_diag_dump() may be still reading
smc->clcsock, therefore this could cause a use-after-free as
reported by syzbot.

Reported-and-tested-by: syzbot+fbd1e5476e4c94c7b34e@...kaller.appspotmail.com
Fixes: 51f1de79ad8e ("net/smc: replace sock_put worker by socket refcounting")
Cc: Ursula Braun <ubraun@...ux.ibm.com>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.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 c4da4a78d369..c4e56602e0c6 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -146,6 +146,9 @@ static int smc_release(struct socket *sock)
 		sock_set_flag(sk, SOCK_DEAD);
 		sk->sk_shutdown |= SHUTDOWN_MASK;
 	}
+
+	sk->sk_prot->unhash(sk);
+
 	if (smc->clcsock) {
 		if (smc->use_fallback && sk->sk_state == SMC_LISTEN) {
 			/* wake up clcsock accept */
@@ -170,7 +173,6 @@ static int smc_release(struct socket *sock)
 		smc_conn_free(&smc->conn);
 	release_sock(sk);
 
-	sk->sk_prot->unhash(sk);
 	sock_put(sk); /* final sock_put */
 out:
 	return rc;
-- 
2.20.1