linux-kernel - [PATCH 4.20 031/111] smc: move unhash as early as possible in smc

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Date:   Mon, 21 Jan 2019 14:42:25 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ursula Braun <ubraun@...ux.ibm.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        syzbot+0bf2e01269f1274b4b03@...kaller.appspotmail.com,
        syzbot+e3132895630f957306bc@...kaller.appspotmail.com,
        "David S. Miller" <davem@...emloft.net>,
        syzbot+fbd1e5476e4c94c7b34e@...kaller.appspotmail.com
Subject: [PATCH 4.20 031/111] smc: move unhash as early as possible in smc_release()

4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Cong Wang <xiyou.wangcong@...il.com>

[ Upstream commit 26d92e951fe0a44ee4aec157cabb65a818cc8151 ]

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>
Reported-by: syzbot+0bf2e01269f1274b4b03@...kaller.appspotmail.com
Reported-by: syzbot+e3132895630f957306bc@...kaller.appspotmail.com
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/smc/af_smc.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -146,6 +146,9 @@ static int smc_release(struct socket *so
 		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 *so
 		smc_conn_free(&smc->conn);
 	release_sock(sk);
 
-	sk->sk_prot->unhash(sk);
 	sock_put(sk); /* final sock_put */
 out:
 	return rc;