[Patch net] smc: move unhash as early as possible in smc_release()

[Cong Wang]

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+fbd1e5476e4c94c7b...@syzkaller.appspotmail.com
Fixes: 51f1de79ad8e ("net/smc: replace sock_put worker by socket refcounting")
Cc: Ursula Braun <ubr...@linux.ibm.com>
Signed-off-by: Cong Wang <xiyou.wangc...@gmail.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