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Subject[PATCH 4.20 031/111] smc: move unhash as early as possible in smc_release()
Date
4.20-stable review patch.  If anyone has any objections, please let me know.

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

From: Cong Wang <xiyou.wangcong@gmail.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@syzkaller.appspotmail.com
Fixes: 51f1de79ad8e ("net/smc: replace sock_put worker by socket refcounting")
Cc: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reported-by: syzbot+0bf2e01269f1274b4b03@syzkaller.appspotmail.com
Reported-by: syzbot+e3132895630f957306bc@syzkaller.appspotmail.com
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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;

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